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Recovery of heavy metals from canola (Brassica napus) and soybean (Glycine max) biomasses using electrochemical process
Journal Pre-proof Recovery of heavy metals from canola (Brassica napus) and soybean (Glycine max) biomasses using electrochemical process Aydeniz Demir Delil, Nurcan Köleli, Hatice Da˘ghan, Gizem Bahçeci
PII: DOI: Reference:
S2352-1864(18)30007-5 https://doi.org/10.1016/j.eti.2019.100559 ETI 100559
To appear in:
Environmental Technology & Innovation
Received date : 4 January 2018 Revised date : 18 November 2019 Accepted date : 23 November 2019 Please cite this article as: A.D. Delil, N. Köleli, H. Da˘ghan et al., Recovery of heavy metals from canola (Brassica napus) and soybean (Glycine max) biomasses using electrochemical process. Environmental Technology & Innovation (2019), doi: https://doi.org/10.1016/j.eti.2019.100559. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
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Recovery of Heavy Metals from Canola (Brassica napus) and Soybean (Glycine max) Biomasses Using
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Electrochemical Process
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3 Aydeniz Demir Delil1*, Nurcan Köleli2, Hatice Dağhan3, Gizem Bahçeci1
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33343, Mersin, Turkey
Department of Civil Engineering, Faculty of Engineering and Architecture, Arel University, Istanbul, Turkey
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Department of Soil Science and Plant Nutrition, Faculty of Agriculture, University of Eskişehir Osmangazi, TR-
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Department of Environmental Engineering, Faculty of Engineering, Mersin University, Çiftlikköy Campus, TR-
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26160 Eskişehir, Turkey
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*Corresponding Author:
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Assist. Prof. Dr. Aydeniz Demir Delil
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Mersin University, Faculty of Engineering
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Department of Environmental Engineering
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33342 Mersin-Turkey
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E-mail: [email protected]
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ABSTRACT
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Phytoextraction is defined as the process by which metal-accumulating plants concentrate metals from the soil into the
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harvestable green parts of the plant above ground. However, the main problem after phytoextraction is that the plants
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(hyperaccumulators) accumulated metal are defined as secondary contaminants and classified as hazardous wastes
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since they include an excessive amount of metals. Hence, plant waste utilization after phytoextraction processes is still
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a challenge that remains to be solved. In this study, canola (Brassica napus) and soybean (Glycine max) were used for
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remediation of heavy metals (Cd, Pb and Zn) contaminated. Two different extraction methods were used to dissolve
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heavy metals in waste biomass. The extraction method, in which the highest efficiency was combined with an
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electrochemical reduction to remove/recover toxic metals from the biomass of canola and soybean, harvested after
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phytoextraction. Firstly, the heavy metal ions were transferred into the solution from biomass. Then these toxic metal
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ions were removed electrochemically within 2 h. Thus, the toxic ions, causing contamination, were transformed
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directly into metallic form by reducing the concentration (metal recovery). We obtained electrochemical removal
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efficiencies of 80% for Cd, 94% for Pb and 68% for Zn in the solution of soybean biomass while they were 97% for
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Cd, 99% for Pb and 46% for Zn in the solution of canola biomass.
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Keywords: Combined system, contaminated biomass, electrodeposition, heavy metals, phytoextraction, canola and
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soybean
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1. Introduction
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Among of the major problems which today’s world encounters, environmental pollution increases year by
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year and damages earth irrecoverably. Environmental pollution comes into existence as soil, air, water pollution and
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affects the whole ecosystem human being also included (Zhang et al. 2015). One of the main sources of pollution is
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anthropogenic sources because of exceeding the assimilative capacity of the receiving environment where it occurs.
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The soil ecosystem, one of the natural and non-renewable sources, is exposed to organic and inorganic contaminants
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as a result of recent industrial developments and agricultural activities (especially heavy metals). Soil contamination
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and its control is one of the most challenging subjects of environmental engineering. Further, heavy metals are the
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most hazardous soil contaminants, creating serious risks of human and animal health (Balkhair et al. 2016).
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Heavy metals exist within the soils naturally; however, their concentration in soil increases due to
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anthropogenic activities such as the excessive and unconscious use of pesticides, wastewater discharges and sludge.
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Since heavy metals are unable to be broken down biologically, their excessive amount of accumulation and
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transportation from plants to animals and humans through the food chain, as a result of long exposition, may cause
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dangerous consequences in terms of toxicity (Lu et al. 2017).
Many treatment technologies were developed in order to decrease heavy metals from soil. Phytoremediation
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technologies have recently become attractive solutions since they are applicable, cost-efficient and provide an in-situ
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treatment for the removal of heavy metals from soil (Ali et al. 2013; Gramss et al. 2011).
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The phytoremediation method aims to cultivate heavy metal tolerant plants through the ability of heavy metal
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uptake into the plant tissue during their metabolic processes (Cuypers et al. 2013). Using hyper accumulator plants
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during phytoremediation method enables to provide more productive results. The reason to use those plants is that they
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are able to accumulate 50 to 500 times more metal in their tissues.
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Phytoremediation processes take different kind of names depending on the pollutants, levels of pollution and
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plant species (Padmavathiamma and Li, 2007). Phytoremediation is a technique which uses plants to cleanup organic
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and inorganic pollutants from the contaminated soil, water and air.
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The names of the methods differ in terms of pollutant types and contaminated areas (soil-air or water), such as
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rhizofiltration, phytodegradation, phytoextraction, phytovolatilization, phytostabilization and rhizodegradation.
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contamination through plant roots. A plant used for phytoextraction is required to accumulate a high amount of metal,
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grow rapidly, be deep-rooted, be easily harvested and to have a high tolerance towards heavy metal. In that manner,
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we used, canola (Brassica napus) and soybean (Glycine max) plants which were preferred regarding their properties
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such as oil ratio, efficiency, industrial value, irrigation and fertilizer etc. Those plants are growing rapidly and having
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high biomass and oil in their seed.
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However, the most significant problem after phytoextraction is that the hyperaccumulator plants are identified
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as secondary pollutants because of containing an excessive amount of heavy metals in its tissues and have been
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classified as hazardous waste. Phytoremediation technique contributes huge quantities of contaminated materials to
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the environment and creates further pollution problems (Mohanty, 2016). That is why, phytoremediation technologies
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are usually not considered as final removal methods. Subsequently, an additional treatment such as composting,
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compacting, incineration, pyrolysis and direct disposal are applied to the contaminated plant biomass after
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phytoextraction. Composting and compaction terms are defined as pre-treatment processes causing biomass to be still
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classified as hazardous waste (Sas-Nowosielska et al. 2004). However the incineration process causes air pollution.
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Pyrolysis, on the other hand, is a cost-intensive method which has infrequently been applied in many countries.
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Due to these negative feedbacks written above, a new method is required for the metal recovery from biomass
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classified as hazardous waste, containing heavy metals. The important point; metal recovery from plant waste, instead
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of direct disposal of the harvested plant, is more applicable and economically importance option. In this study, recovery
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of the heavy metals in biomass through electrochemical method is investigated as an alternative to other methods.
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Electrochemical treatment, which is one of the promising methods in recent years, has some features such as recovery
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of metals, low cost, simple operation, slight amount of chemical usage and combination with other treatment processes
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(Ait Ahmed, et al. 2016; Chen, 2004).
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Some researchers have combined electrokinetic method with phytoremediation to remove residual
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contamination and succeed to have cleaner soil in the field. Jiang, et al. (2015) have pursued a radical approach to
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solve the problem of eliminating the plant biomass by thermo-chemically converting renewable energy, and they have
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designed a metal recovery process from waste biomass.
102 Chirakkara et al. (2015) examined on combining an electrokinetic remediation with phytoremediation for a
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soil co-contaminated with heavy metals and PAHs. They had grown oat plant and sunflower in the electro-kinetic cell
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for 30 days. The results showed that the heavy metals and organic pollutants in the soil were significantly reduced.
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However, biomass production of the plants increased with the application of electric current, but there was no
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significant improvement in heavy metal phytoextraction or PAH degradation.
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Mao et al. (2016) examined the processes of coupled electro-kinetic phytoremediation of polluted soils to
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remove Pb, As and Cs. They showed that the solubility and bioavailability of Pb, As and Cs were significantly
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enhanced by the electro-kinetic field (EKF). The electro-kinetic field treatment was efficient in lowering soil pH near
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to the anode which is beneficial for the dissolution of metals. The bioaccumulation of Pb, As and Cs were all increased
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upon EKF treatment, indicating the EKF treatment might have been a good alternative for increasing phytoextraction
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efficiency of Pb, As and Cs.
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However, this study is completely different from the studies mentioned above, in which electro-kinetic
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method and phytoremediation are combined. The aim of this study is to recover heavy metals from waste plants
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obtained electrochemically after phytoextraction. In this study, electrolysis reactions were used for metal recovery and
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toxic metals were recovered in biomass by the electro-reduction method. Electrochemical reduction brought originality
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to the study as it enabled the recovery of metals with high economic value. It also provided a treatment of the biomass,
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containing toxic metals by the “zero waste” principle.
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First, canola (Brassica napus) and soybean (Glycine max) plants were cultivated in multi heavy metal (Cd,
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Pb and Zn) contaminated soil for phytoextraction. Afterwards, the accumulated heavy metals in biomass were turned
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into ionic form through microwave extraction and then converted into metallic form through electrochemical reduction.
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This integrated study has shown that biomass within the scope of hazardous waste can be treated and included in the
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non-hazardous waste class after phytoextraction.
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2. Material and Method
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2.1. Soil and Plant Materials
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In this study, the coordinates of both contaminated (Cd, Pb and Zn) and uncontaminated soil samples were
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determined with Global Positioning System (GPS). The soil contaminated with multi-metal and the one
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uncontaminated were collected from 0-30 cm depth in Kayseri-Incesu (38° 42' 43" N and 35° 15' 55" E) and Copurlu
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Village, located on the way to Mersin-Gözne (36° 87' 32" N and 34° 56''50" N), respectively. The study areas were
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shown in Figure 2.1.
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Figure 2.1. Soil sampling areas
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Canola and soybean plants were grown under controlled environment conditions (50-60% humidity, 16 h of
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light and 8 h of dark photoperiod, 25±2oC temperature and 1500 Lux light intensity) in the climate chamber for 3
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months. Ten canola and 10 soybean seeds were planted in pots during the experiment. All of the plants were irrigated
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regularly and the water-holding capacity of the soil was stabilized at approximately 70% (under field conditions).
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The soil contaminated with higher multi-metal concentration was mixed with the one uncontaminated as 0%
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(controlled clean soil), 25%, 50%, 75% and 100% proportions. Canola and soybean plants were grown in the obtained
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five soil mixtures. The experimental plan was designed with randomized block method in three replicates.
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2.2. Soil and Plant Analyses
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The soil samples were air dried at the room temperature and then sieved from 4 mm sieve for pot experiments.
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For some, physical and chemical analyzes, soil samples were used which passed through a 2 mm. Soil samples were analyzed for pH in a 1:1 (m:v) ratio of soil to water solution, the soil texture was determined
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according to the hydrometer method, the organic matter by modified Walkley–Black titrations and lime by the
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calcimeter method. Total metal analysis of the soil was conducted in compliance with the EPA 3051A method and
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concentrations of the metals were detected with the Agillent brand 7500ce model ICP-MS (Inductively Coupled
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Plasma Mass Spectrometer) (USEPA, 1995b). The accuracy of the method was tested with a standard soil certified
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(CRM 7003). Some physical and chemical properties of the soil, regarded as both contaminated and uncontaminated,
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and initial metal contents were detected. The values determined by Ciftçi (2016) are shown in Table 2.1.
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Table 2.1. Some physical and chemical properties and standard deviations of the uncontaminated and
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contaminated soil samples (n=3) (Çiftçi, 2016)
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As seen in Table 2.1, pH of the soil was moderate alkaline at 8.0. The texture classification of the soil was
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sandy loam. Lime amount was moderate (7.26) while the amount of organic matter was high (5.27). Whereas the total
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amount of nitrogen (N) was considerably higher, available amounts of phosphor (P) (11.34) and potassium (19.55)
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were also high. According to Kabata Pendias, the critical values for Cd, Pb and Zn were between 3-8, 100-400 and 70-
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100, respectively (Kabata-Pendias, 2007).
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According to EPA Method 3051A (USEPA, 1995b), in contaminated soil, total concentrations of Cd, Pb and
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Zn were determined as 483.70 25755.60 and 13412.20 mg kg-1, respectively. On the other hand, the concentrations of
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Cd, Pb and Zn were determined as 1.92; 92.41 and 19.09 mg kg-1, respectively in uncontaminated soil.
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Canola and soybean were used in the pot experiment as plant materials. After harvesting green parts of the
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canola and soybean with the highest phytoextraction capacity during the trial, the moisture contents were measured
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according to Equation (1) after being kept in a drying oven at 70 °C for 72 h (Kaçar, 1984). All the data obtained from
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the plant material during the research were described as oven dry plant biomass at 70°C.
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𝑀𝑜𝑖𝑠𝑡𝑢𝑟𝑒 𝐶𝑜𝑛𝑡𝑒𝑛𝑡
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Harvested canola and soybeans were grinded and solubilized in the microwave oven for 45 minutes with 0.2 g, of
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which is 2 mL deionized water, 2 mL with 35% H2O2 and 4 mL with 65% HNO3.The heavy metal concentration (Cd,
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Pb, Zn) of plant samples were determined by ICP-MS. The accuracy of the analysis was controlled with a standard
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certificate plant (CRM 1573A-tomato leaf) sample. The concentrations of Cd, Pb and Zn were determined as 0.980,
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1.840 and 84.860 mg kg-1, respectively in the standard certified plant sample. Cadmium, Pb and Zn concentrations on
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CRM 1573A-tomato leaf were 0.978, 1.846 and 85.000 mg kg-1, respectively. As can be seen in the results, both values
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were close to each other.
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2.3. Electrochemical Experimental Setup
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Batch electrochemical tests were carried out in an electrochemical glass cell, which was divided into two with
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a permeable filter. For the electrochemical reduction, platinum anode (electrode surface 2 cm2) and Pb cathode
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(electrode surface 2 cm2) were used. A power supply was used in order to provide the constant current during
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electrochemical reduction. The voltage was held stable for each run with a retention time for 2 h.
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2.4. Determination of the Effect of Incineration Temperature on Dry Mass Extraction of toxic metals in the waste of biomass is important and dissolution process is carried out after
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incineration method. For this purpose, 1 g of the grinded plant samples was weighed and put into porcelain crucibles.
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In order to determine the effect of the incineration temperature on dry mass loss and metal solubility, plants were
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incinerated in the ash furnace for 8 h at 105°C, 205°C, 305°C, 405°C and 505°C, respectively. Plant samples required
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for electrochemical tests were incinerated at 505 °C in the ash furnace because the maximum metal solubility was
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achieved at this temperature.
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2.5. Determination of the Effect of Extraction Methods on Metals Solubility
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Two different methods were used to extract the metal accumulated in the biomasses. The chemical extraction
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method was compared with the microwave method in terms of extracting Cd, Pb and Zn concentrations. In order to
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transfer the Cd, Pb and Zn accumulated by canola and soybean into the solution, a chemical extraction was performed
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with 0.2 M HCl solution. After the incineration temperature is determined, 1 g plant sample incinerated at 505 °C was
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solubilized in hot plate with 100 mL of 0.2 M HCl for 2 h.
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For the other extraction method, 1 g of the plant sample was digested in 5 mL of deionized water, 5 mL of 35% H2O2
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and 10 mL of 65% HNO3 for 45 minutes in microwave at 150 °C and pressure of 200 psi. After cooling, the solutions
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were completed up to 100 mL final volume with distilled water and passed through a 0.45 μm filter. Then, the total
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heavy metal concentrations were determined by ICP-MS.
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2.6. Electrochemical Reduction Experiments
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Optimum reduction potentials of Cd, Pb and Zn ions were determined in Cyclic Voltammetry by the addition
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of standard solution, which was containing 25 mg L-1 Cd, Pb and Zn (titrisol) in 50 mL of control plants extracted with
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0.2 M HCI before starting the electrochemical reduction processes. After the optimization processes, during which
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the reduction potential was identified, electrochemical removal efficiencies of Cd, Pb and Zn were determined in the
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microwave extracting solution from canola and soybean biomass. The electrochemical reduction process in the
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solutions was conducted at -0.6 V electrode potential.
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Electrodeposition processes in microwave extracting solutions were realized during 2 h by taking 0.5 mL
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solution from the electrochemical cell at regular intervals (0, 15, 30, 45, 60, 90 and 120 min) at constant voltage. The
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electrochemical removal efficiency (ERE) of Cd, Pb and Zn in the cell,depending on time, were calculated in Equation
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(2), where Co is the initial metal ion concentration (mg L-1) in biomass solution and Ce is equilibrium metal ion
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concentration in treated solution at any time (mg L-1).
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𝐸𝑅𝐸 %
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(2)
2.7. Statistical Analysis
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The interaction between temperature (T), dry mass (DM) and solubility of metal ions was performed for canola and
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soybean using the statistical package Statistical Product and Service Solutions (SPSS) 17.0 for Window. The methods
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included one-way analysis of variance (ANOVA) and linear regression analysis. Duncan's multiple range test was used
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to determine the statistical significance (p< 0.05).
3. Results and Discussion
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3.2. Total Metal Concentrations of Plants
In this study, a soil sample with higher metal concentration was mixed with the uncontaminated soil samples
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as 0% (controlled clean soil), 25%, 50%, 75% and 100%.
The overall picture in the pre-harvest of the grown canola and soybean in soil mixtures are shown in Figure
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3.1a-b. The green parts of the canola (shoot) and soybean grown in contaminated soil (100%) were used as plant
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material and the used materials were also shown with arrow marks.
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Figure 3.1. Overall picture of the pre-harvest a) canola (Brassica napus) and b) soybean (Glycine max)
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plants in the soil mixtures used for experimental studies (Left to right 0% (controlled and clean soil), 25%, 50%, 75%
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and 100% polluted)
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in microwave, were compared with the normal and critical concentrations of Cd, Pb and Zn in plants according to
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Kabata-Pendias, (Table 3.1). It was observed that both plants accumulate metal ions in shoots. As can also be seen in
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Table 3.1, Cd, Pb and Zn concentrations, especially in the shoots of the canola were considerably higher than those of
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the normal concentration, threshold value and critical concentration value.
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Evaluated in terms of total Cd, Pb, Zn concentrations, canola accumulated 5 times more Cd, 7 times more Pb
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and 3 times more Zn than that of soybeans. On the other hand, when evaluating total Cd, Pb and Zn concentrations in
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terms of hyperaccumulation threshold limit, it was seen that the soybean plant accumulated 2.4 times more Cd and the
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canola plant accumulated 11 times more Cd and 3.6 times more Pb.
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251 252 Table 3.1. Initial total multi-metal concentration within the shoot of soybean and canola, normal and critical
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concentration range and hyperaccumulation threshold value of the plant (Kabata-Pendias, 2007; Baker and Brooks,
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1989).
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Hyperaccumulator plants are described as the type of plants, which can include more than 100 mg kg-1 Cd,
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1000 mg kg-1 Pb and 10.000 mg kg-1 Zn (Baker and Brooks, 1989). According to this definition, canola is
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hyperaccumulator in terms of accumulated Cd (1134 mg kg-1) and Pb (3682 mg kg-1) concentration while soybean is
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defined hyperaccumulator in terms of Cd (238 mg kg-1). The success of the phytoextraction method depends on the
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plant biomass production and the ability to uptake high amounts of metals in plant shoots (USEPA, 1995a).
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3.3. Effects of Incineration Temperature on Biomass
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In the evaluation of wastes of plant, pre-treatment at high temperatures leads to mass reduction, which is
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important for the disposal of waste after phytoextraction and phytomining.
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To determine the effect of incineration temperature on dry mass, dry masses of soybean and canola incinerated
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for 8 h in ash furnace at 105°C, 205°C, 305°C, 405°C and 505°C, respectively. The absolute moisture content (105°C)
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was determined as 2.4% and 12.34% of soybean and canola, respectively. The significant difference is about the
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tolerance shown towards increased Cd, Pb and Zn concentrations of the canola and soybean within the soil, which was
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shown in Figure 3.1. Whereas soybean was drying (necrosis) in accordance with the increasing dosage, canola
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continued to grow showing tolerance to metals. One of the reasons for this situation might be the fact that canola holds
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more humidity. Figure 3.2 shows the effect of the incineration temperature on the dry mass.
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Figure 3.2. Effect of temperature on dry masses of canola and soybean plant
278 The overall accepted temperature for incineration of plant materials was 450°C. Because evaporation losses
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at these temperatures were low in general and it was sufficient for the complete oxidation of the organic substance. It
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has been reported by Hoenig (1995) that temperatures as high as 520 °C do not cause losses of volatile elements such
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as Cd, Pb or Zn, if the programmed temperature curve is sufficiently low in the ash furnace (Hoenig et al., 1995).
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Therefore, the maximum temperature of the study was chosen as 505°C.
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As it was shown in Figure 3.2, green parts of both plants decreased significantly with temperature increase.
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According to linear regression between the dry mass of canola and the T, it seen that there is a very strong positive
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correlation between two parameters (r=0.96) and this relationship was found to be a high significance as statistically
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(0.001< p<0.01). According to simple linear regression between the dry mass of soybean and the T, there is a very
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strong positive correlation between two parameters (r=0.97) and this relationship was found to be a significance as
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statistically (0.001
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With a theoretical calculation, considering that decrease, performed at 505°C for 1 ton of plants, biomasses
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of canola is going to scale down as 214.8 kg and soybean as 127.9 kg. This means that canola, which is accumulating
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more metal, is more effective compared to soybean in terms of phytomining. As the mass of the plants, which was
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considered as waste after phytoextraction, decreases, the application of pre-treatment methods such as incineration
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method was in the foreground. The incineration method also reduces the cost of treatment and the transportation to the
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landfill. However, a substantial amount of contaminants can still be in the ash even after the incineration process. In
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this study, recovery of the metals from the residual ash was provided after incineration and solubilizing, consecutively.
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3.4. The Effect of Extraction Methods on Metals Solubility
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In the evaluation of the products after phytoextraction, the applied extraction process for transferring Cd, Pb
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and Zn from plants to the solution was very significant. Acid extraction (dissolution) is applied mostly through the
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method of incineration methods in order to extract toxic metals from plants after phytoextraction (Zarcinas et al. 2007).
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During metal extractions from organic matrix like plants; hydrofluoric acid (HF), hydrochloric acid (HCI), nitric acid
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(HNO3), perchloric acid (HCIO4) and sulphuric acid (H2SO4) are used individually or in mixtures (Idera et al., 2014).
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Before electrochemical reduction process, Cd, Pb and Zn concentrations transferred from waste plant
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materials (biomass) into the solution are important. In order to determine the concentration of metal ions, biomasses
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were incinerated by keeping in the ash furnace for 8 h at 105 °C, 205°C, 305°C, 405°C and 505°C, respectively, and
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then extracted with 0.2 M HCI. Total metal concentrations in canola and soybean after the acid extraction process were
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shown in Figure 3.3a-b.
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According to linear regression analysis between the solubility of Cd, Pb and Zn in the canola biomass and the
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T, there is a very strong correlation between the two parameters (r =0.92, 0.87 and 0.93) and this relationship was
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found to be borderline significance as statistically (0.05
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Figure 3.3. Effect of temperature and 0.2 M HCI on metal concentration; a) extracted from canola and b) extracted
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from soybean
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According to linear regression between the solubility of Cd in the soybean biomass and the T, there is a very
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strong positive correlation between two parameters (r=0.96) and this relationship was found to be a significance as
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statistically (0.001
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there is a very strong positive correlation between two parameters (r =0.99) and this relationship was found to be a
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very high as statistically (p<0.001). However, in the statistical analysis for Zn, it seen that there is a weak correlation
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between the two parameters (r =0.73) and this relationship was found to be insignificant as statistically (p>0.1).
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The Cd, Pb and Zn concentrations of samples incinerated in the ash furnace at 505 °C and then extracted with
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0.2 M HCI was compared with the performed microwave method results in same samples. Total metal concentration
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of the solubilized from waste of plants through two different methods were shown in Table 3.2.
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Table 3.2. Total metal concentration of solubilized from canola and soybean plants, both through ash furnace and
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microwave methods (mg kg-1)
When the table was examined, it can be seen that the solubilized metal amount with ash furnace was less than
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that of the microwave method.
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After ash furnace method, the percentages of extracted Cd, Pb and Zn from canola and soybean were found
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as 16%, 1% and 8% and 13%, 14% and 11%, respectively. Effectiveness of chemical reagent during metal extraction
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changed depending on initial metal concentration, pollutant types, extraction properties and experimental conditions
336
(Hoenig et al. 1995). Since initial metal concentrations in the soybean plant are lower than that of canola, the percentage
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of extraction obtained from the soybean was higher than the canola. Metal concentrations of the plant samples digested
338
in the microwave were found higher than that of those conducted with ash furnace. Thus, the plant solution extracted
339
with the microwave method was used in the electrochemical reduction tests.
There are limited numbers of studies in literature, in which the about of evaluation of wastes of plant after
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phytoextraction.
Yıldırım (2016) stated in her study, which was conducted for the evaluation of metals in safflower and castor
343
oil plants, that Cd, Pb and Zn concentration extracted with 1.0 M H2SO4 was higher than that of with 0.5 M H2SO4.
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However, the researcher indicated that Cd, Pb and Zn concentration transmitted into solution after extraction was
345
unable to reach the total metal concentration extracted through the microwave method (Yıldırım, 2016). For this reason,
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it was one of the most important conditions that the toxic metals in the biomass were passed to the solution in high
347
percentages.
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Hetland et al. (2001) utilized chelating agents (EDTA and N-(2-acetamido) iminodiacetic acid) for the purpose
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of recovery of the Pb from harvested biomass after phytoremediation. Researchers were able to extract 98.5% of Pb
350
with EDTA at pH 4.5 after two series of washing. They reduced the Pb concentration from 2000 mg kg-1 to 30 mg kg-
351
1
352
hazardous waste after the extraction (Hetland et al. 2001).
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after liquid extraction from residual biomass. Thus, the plant biomass, initially defined as hazardous waste, was not
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Ginneken et al. (2007) used phytoextraction method in Belgium for the treatment of the soils contaminated
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with heavy metals. Besides, they used plant biomass obtained after phytoextraction for anaerobic decomposition,
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incineration, gasification and the biodiesel produced from seed. The grain or seed of the canola plant used in this study
356
could be utilized as raw material for biodiesel production (Ginneken et al., 2007). Many biodiesel types, which are
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considerably used today, are produced from the oils of edible plants such as canola, soybean and sunflower (Silitonga
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et al. 2015).
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According to Jiang et al. (2015) recycling of metals is critical to the sustainability of industrial development,
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as natural reserves are depleting. However, despite the increased demand, none of the resources have been backed by
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recycling, as the recovery of low metal concentrations is costly compared to conventional mining. The recovery of the
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elements may be lower than the cost of disposal of potentially toxic biomass in large quantities. The market value of
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the element for the recovery of biomass heavy metals is quite determinative. In such an application, metal recovery
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values are reduced from the plant's planting and maintenance costs (Jiang et al. 2015).
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3.5. Electrochemical Removal of Metal Ions Transferred to Solution and Effect of Contact Time on Metal
367
Recovery
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The harvested canola and soybean plants were grinded and solubilized by the microwave method and the
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electrochemical reduction solution was prepared. After the initial metal concentrations (Ce) of the prepared solution
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have been determined, Electrochemical reduction tests were performed in a 150 mL of the solution at -0.6 V electrode
372
potential depending on time. Initial metal concentrations (Ce) in the solution obtained from biomass of canola and
373
soybean with the microwave method for Cd, Pb and Zn were determined as 1134, 3682 and 6169 mg L-1 and 238, 554
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and 2380 mg L-1, respectively.
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The change of metal ions concentrations with electrochemical removal tests were shown in Figure 3.4a-b. As
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it is shown in Figure; Cd, Pb and Zn concentrations reduced homogeneously in the whole solution.
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Figure 3.4. Time-dependent change of metal ions concentration at -0,6 V electrode potential in the extracted solution
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from plants; a) electrochemical removal of metal ions in the solution obtained from biomass of canola b)
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electrochemical removal of metal ions in the solution obtained from biomass of soybean
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Electrochemical removal efficiencies measured in accordance with the initial metal concentration for biomass
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of canola and soybean were shown in Figure 3.5a-b.
In the first 30 minutes; Cd, Pb and Zn were removed by about 91%, 97% and 41%, respectively, in the
385
electrochemical cell from the solution of canola biomass. At the end of 2 h, the removal efficiencies were calculated
386
97% for Cd, 99% for Pb and 46% for Zn (Fig.3.5a).
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Figure 3.5. Time-dependent change of the removal efficiencies of Cd, Pb and Zn at -0.6 V electrode potential in the
389
extracted solution from plants; a) change of electrochemical removal efficiency in the solution obtained from biomass
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of canola b) change of electrochemical removal efficiency in the solution obtained from biomass of soybean
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The removal efficiency in the electrochemical cell with regard to the initial metal concentration in solution of
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soybean biomass was shown in Figure 3.5b. At the end of 2 h, the electrochemical removal efficiencies for Cd, Pb and
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Zn were found 80%, 94% and 68%, respectively.
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The yield of electrochemical metal removal in soybean plant, which has less metal accumulation compared
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to canola, was found to be high. It was concluded that after conducting the first step with high efficiency, the recovery
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of metals was also higher by electrochemical method.
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The findings were compatible with the results of the study by Yıldırım (2016) and Eke (2010), conducted for
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the utilization of safflower (Carthamus tinctorius), castor oil (Ricinus communis) and Ni hyperaccumulator Thlaspi
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elegans Boiss plant after phytoextraction.
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After the electrochemical process, the reduced metal ions from the extraction solution of the canola biomass
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were separated from the surface of the Pb electrode by scraping. The scraped metal was considered as the recovered
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quantity and approximately 0.0048 g of solid material was obtained after electrodeposition. The solid material was
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defined as inert due to its metallic formation. The solid material obtained was dissolved in concentrated HF and 1:3 ratio of HCI and it was determined
406
quantitatively by ICP-MS in order to find out whether it includes Cd, Pb and Zn. Since the reduction process takes
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place on the Pb electrode (cathode), Pb concentration was neglected, but Cd and Zn concentration was determined in
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the solution. The transformation of Cd, Pb and Zn ions into electrochemically reduced metallic form after
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phytoextraction, is very important from an environmental point of view. These metals are classified as precious metals
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and quite overpriced (Cd-3750 $ ton-1, Pb-817 $ ton-1 and Zn-1007 $ ton-1). In other words, it will contribute to the
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economy of the country with the electro-recovery process (Robinson et al. 1997).
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This study revealed that extracting toxic metals from the biomass of plants with a decent
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extraction/solvent/acid with maximum efficiency is the most important step in metal recovery. As a result of the high
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extracting of the metal ions from biomass, the maximum recovery can be carried out by electrochemical reduction.
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4. Conclusions
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In this study, a considerable amount of metal removal was provided through electrochemical reduction from
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extracted solutions obtained from canola and soybean biomass. The contamination of soil with more than one metal
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has reduced the phytoextraction yield of plants. It was determined that the soybean was not a suitable plant for
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phytoextraction because the efficiency of phytoextraction in this plant was lower than canola.
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The electrochemical reduction method tested in this study can be defined as a significant method for the
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removal of toxic effect and recover valuable metals. The extraction process conducted by the microwave method was found to be more effective than ash furnace
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method with 0.2 M HCl. The extraction process is very important for the second step (electro-recovery) and more
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studies are required to be conducted to increase the recovery efficiency.
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The implementations of microwave method and following usage of the electrochemical reduction provide
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metal ion removal and metal recovery. The recommended combined method is an alternative advanced technique that
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can be used instead of composting and compaction, combustion and gasification in the assessment of contaminated
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plants.
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Acknowledgements
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This research was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) Project
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No: 115Y337 and the Mersin University Scientific Research Project (MEÜ BAP) Unit with 2017-2-TP2-2579.
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This academic work was linguistically supported by the Mersin Technology Transfer Office Academic Writing Center
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of Mersin University.
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Baker A J M, Brooks R (1989) Terestrial Higher Plants Which Hyperaccumulate Metalic Elements: A Review of Their
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Distribution, Ecology and Phytochemistry. Biorecovery 1(2): 81-126
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Balkhair KS, Ashraf MA (2016) Field accumulation risks of heavy metals in soil and vegetable crop irrigated with
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Chen G (2004) Electrochemical technologies in wastewater treatment. Sep. Purif. Technol. 38(1), 11–41
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Chirakkara RA,
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Çiftçi A (2016) Multimetal (cadmium, lead and zinc) treatment of soil contaminated with a wild indian oil (Ricinus
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Cuypers A, Remans T, Weyens N, Colpaert J, Vassilev A, Vangronsveld J (2013) Soil–plant relationships of heavy
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Eke M (2010) The study of nickel acid extraction and electrochemical metal recovery from nickel hyperaccumulator
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Thlaspi elegans Boiss. Dissertation, Mersin University
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Ginneken VL, Meers E, Guisson R, Ruttens A, Elst K., Vangronsveld J, Diels L, Dejonghe W (2007) Phytoremediation
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Gramss G, Voigt KD, Merten D (2011) Phytoextraction of heavy metals by dominating perennial herbs. In: Merkel B,
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Hoenig M (1995) Critical discussion of trace element analysis of plant matrices. Sci Tot Environ 176: 85–91
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Idera F, Omotola O, Paul UJ, Adedayo A (2014) Evaluation of the effectiveness of different acid digestion on
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Jiang Y, Lei M, Duan L (2015) Integrating phytoremediation with biomass valorisation and critical element recovery:
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Loeppert RH, Suarez DL (1996) Carbonate and gypsum, In: Sparks DL (ed), Methods of soil analysis. 3rd edn. WI:
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Richards LA (1954) Diagnosis and improvement saline and alkaline soils. US Dep Agr Handbook 60 Government
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Robinson BH, Chiarucci A, Brooks RR, Petit D, Kirkman JH, Gregg PEH, Dominicis V (1997) The nickel
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hyperaccumulaor plant Alyssum bertolinii as a potential agent for phytoremediation and phytomining of Nickel. J
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Silitonga AS, Masjuki HH, Mahlia TMI, Ong HC, Kusumo F, Aditiya HB, Ghazali NNN (2015) Schleichera oleosa
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L. oil as feedstock for biodiesel production. Fuel 156:63-70.
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Soil Survey Staff (1951) Soil Survey Manual. US Dept Agr Handbook No:18, US Government Print Office,
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Washington.
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USEPA (1995a). Contaminants and remedial options at select metals-contaminated sites. EPA/540/R-95/512.6. US
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Environmental Protection Agency, Washington.
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USEPA (1995b.) Test Methods for Evaluation of Solid Waste vol. IA, Laboratory Manual Physical/Chemical Methods,
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SW 846, 40 CFR Parts 403 and 503, 3rd (ed), US Government Printing Office, Washington.
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Yıldırım, D., 2016. The removal/recovery of heavy metals from castor (Ricinus communis) and safflower (Carthamus
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tinctorius) plants after phytoremediation by electrochemical method. Dissertation, Mersin University
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Zarcinas BA, Cartwright B, Spouncer L (1987) Nitric acid digestion and multi-element analysis of plant material by
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inductively coupled plasma spectrometry. Commun Soil Sci Plan 131-146
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Zhang X, Zhong T, Liu L, Ouyang X (2015) Impact of soil heavy metal pollution on food safety in China. Plos
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533 534 Figure List
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Figure 2.1. Soil sampling areas
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Figure 3.1. Overall picture of the pre-harvest a) canola (Brassica napus) and b) soybean (Glycine max) plants in the
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soil mixtures used for experimental studies (Left to right 0% (controlled and clean soil), 25%, and 50%, 75% and 100%
553
polluted)
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a)
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Canola (Brassica napus)
556 557 558 559 560
b) Soybean (Glycine max)
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Figure 3.2. Effect of temperature on dry masses of canola and soybean plant (mean ±SD, n=3)
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Figure 3.3. Effect of temperature and 0.2 M HCI on metal concentration; a) extracted from canola and b) extracted
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from soybean (mean ±SD, n=3)
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a)
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Figure 3.4. Time-dependent change of metal ions concentration at -0,6 V electrode potential in the extracted solution
594
from plants; a) electrochemical removal of metal ions in the solution obtained from biomass of canola b)
595
electrochemical removal of metal ions in the solution obtained from biomass of soybean
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596 597 b)
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Figure 3.5. Time-dependent change of the removal efficiencies of Cd, Pb and Zn at -0.6 V electrode potential in the
604
extracted solution from plants; a) change of electrochemical removal efficiency in the solution obtained from biomass
605
of canola b) change of electrochemical removal efficiency in the solution obtained from biomass of soybean
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a)
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607 608 b)
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Table List
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Table 2.1. Some physical and chemical properties and standard deviations of the uncontaminated and contaminated
615
soil samples (n=3) (Çiftçi, 2016) Soil Properties
Uncontaminated
Contaminated
Soil
Soil
References
20.5±1.1
84.6±2.3
Silt (0,002-0,02 mm) (%)
27.0±0.9
8.4±0.5
Clay (<0.002 mm) (%)
52.5±1.0
7.0±0.6
Texture class
C (Clay)
LS (Loamy sand)
pH (in 1:1 saturated soil)
8.23
8.04
Lime (CaCO ) (%)
28.34
7.26
Organic matter (%)
3.04
5.27
Soil Moisture (%)
5.50±0.54
4.69±0.24
Water saturation (%)
60±1.30
28±0,90
Total N (%)
2.24±0.01
2.10±0.01
Kacar, 1995
Available P (mg P2O5 kg-1)
1.98±0.23
11.34±0.25
Olsen et al., 1982
Available K (mg K2O kg-1)
63.4±3.10
19.55±0.15
Richards, 1954
1.92±0.10
483±32.9
USEPA, 1995b
92.4±3.35
13412±0.1
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EPA 3051A- Total Zn (mg/kg)
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EPA 3051A-Total Cd (mg/kg)
Bouyoucos, 1951
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Sand (0.02-2 mm) (%)
3
Soil Survey Staff, 1951
EPA 3051A- Total Pb (mg/kg)
19.1±0.01
25755±0.54
DTPA extractable Cd (mg/kg)
0.05±0.02
26.8±0.16
Lindsay and Norvell,
DTPA extractable Pb (mg/kg)
1.03±0.21
31.1±1.72
1978
DTPA extractable Zn (mg/kg)
0.75±0.33
128±11.6
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Table 3.1. Initial total multi-metal concentration within the shoot of soybean and canola, normal and critical
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concentration range and hyperaccumulation threshold value of the plant (Kabata-Pendias, 2007; Baker and Brooks,
621
1989).
Normal
Critical
Hyperaccumulation
mg kg-1 DM*
Concentration
Concentration
Threshold Value
Range, mg kg-1
mg kg-1
DM*
DM*
5-30
100
30-300
1000
Range, mg kg-1 Canola
DM*
Cd
238±1.89
1134±12.3
0.10-2.40
Pb
554±8.16
3682±14.12
0.2-20.00
Zn
2380±12.62
6169±15.83
*DM: Dry Mass
623 624
1-400
100-400
10000
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Concentration of Sample
Element
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Table 3.2. Total metal concentration of dissolved canola and soybean plants, both through ash furnace and microwave
633
methods (mg kg-1) Application
Cd (mg kg-1)
Pb (mg kg-1)
Ash Furnace
186±0.10
38±0.03
483±0.45
Microwave
1134±10.69
3682±13.37
6169±25.21
Ash Furnace
31±0.34
Microwave
238±0.58
76±0.48
261±0.41
554±1.32
2380±19.50
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Canola
Soybean
Zn (mg kg-1)
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This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue.
o
The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript
o
The following authors have affiliations with organizations with direct or indirect financial interest in the subject matter discussed in the manuscript:
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Affiliation
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Aydeniz Demir Delil
Mersin University
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Highlights
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Cultivation of canola (Brassica napus) and soybean (Glycine max) plants in contaminated soil with heavy
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metals
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Chemical and microwave extraction exposure of canola and soybean which accumulate heavy metals
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Recovery of heavy metals through electrochemical method from biomass after phytoextraction
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The results of the study show that heavy metals in biomass can be recovered by electrochemically
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PII: DOI: Reference:
S2352-1864(18)30007-5 https://doi.org/10.1016/j.eti.2019.100559 ETI 100559
To appear in:
Environmental Technology & Innovation
Received date : 4 January 2018 Revised date : 18 November 2019 Accepted date : 23 November 2019 Please cite this article as: A.D. Delil, N. Köleli, H. Da˘ghan et al., Recovery of heavy metals from canola (Brassica napus) and soybean (Glycine max) biomasses using electrochemical process. Environmental Technology & Innovation (2019), doi: https://doi.org/10.1016/j.eti.2019.100559. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Recovery of Heavy Metals from Canola (Brassica napus) and Soybean (Glycine max) Biomasses Using
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Electrochemical Process
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3 Aydeniz Demir Delil1*, Nurcan Köleli2, Hatice Dağhan3, Gizem Bahçeci1
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6
1
7
33343, Mersin, Turkey
Department of Civil Engineering, Faculty of Engineering and Architecture, Arel University, Istanbul, Turkey
3
Department of Soil Science and Plant Nutrition, Faculty of Agriculture, University of Eskişehir Osmangazi, TR-
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Department of Environmental Engineering, Faculty of Engineering, Mersin University, Çiftlikköy Campus, TR-
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26160 Eskişehir, Turkey
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*Corresponding Author:
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Assist. Prof. Dr. Aydeniz Demir Delil
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Mersin University, Faculty of Engineering
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Department of Environmental Engineering
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33342 Mersin-Turkey
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E-mail: [email protected]
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ABSTRACT
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Phytoextraction is defined as the process by which metal-accumulating plants concentrate metals from the soil into the
25
harvestable green parts of the plant above ground. However, the main problem after phytoextraction is that the plants
26
(hyperaccumulators) accumulated metal are defined as secondary contaminants and classified as hazardous wastes
27
since they include an excessive amount of metals. Hence, plant waste utilization after phytoextraction processes is still
28
a challenge that remains to be solved. In this study, canola (Brassica napus) and soybean (Glycine max) were used for
29
remediation of heavy metals (Cd, Pb and Zn) contaminated. Two different extraction methods were used to dissolve
30
heavy metals in waste biomass. The extraction method, in which the highest efficiency was combined with an
31
electrochemical reduction to remove/recover toxic metals from the biomass of canola and soybean, harvested after
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phytoextraction. Firstly, the heavy metal ions were transferred into the solution from biomass. Then these toxic metal
33
ions were removed electrochemically within 2 h. Thus, the toxic ions, causing contamination, were transformed
34
directly into metallic form by reducing the concentration (metal recovery). We obtained electrochemical removal
35
efficiencies of 80% for Cd, 94% for Pb and 68% for Zn in the solution of soybean biomass while they were 97% for
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Cd, 99% for Pb and 46% for Zn in the solution of canola biomass.
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Keywords: Combined system, contaminated biomass, electrodeposition, heavy metals, phytoextraction, canola and
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soybean
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1. Introduction
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Among of the major problems which today’s world encounters, environmental pollution increases year by
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year and damages earth irrecoverably. Environmental pollution comes into existence as soil, air, water pollution and
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affects the whole ecosystem human being also included (Zhang et al. 2015). One of the main sources of pollution is
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anthropogenic sources because of exceeding the assimilative capacity of the receiving environment where it occurs.
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The soil ecosystem, one of the natural and non-renewable sources, is exposed to organic and inorganic contaminants
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as a result of recent industrial developments and agricultural activities (especially heavy metals). Soil contamination
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and its control is one of the most challenging subjects of environmental engineering. Further, heavy metals are the
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most hazardous soil contaminants, creating serious risks of human and animal health (Balkhair et al. 2016).
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Heavy metals exist within the soils naturally; however, their concentration in soil increases due to
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anthropogenic activities such as the excessive and unconscious use of pesticides, wastewater discharges and sludge.
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Since heavy metals are unable to be broken down biologically, their excessive amount of accumulation and
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transportation from plants to animals and humans through the food chain, as a result of long exposition, may cause
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dangerous consequences in terms of toxicity (Lu et al. 2017).
Many treatment technologies were developed in order to decrease heavy metals from soil. Phytoremediation
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technologies have recently become attractive solutions since they are applicable, cost-efficient and provide an in-situ
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treatment for the removal of heavy metals from soil (Ali et al. 2013; Gramss et al. 2011).
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The phytoremediation method aims to cultivate heavy metal tolerant plants through the ability of heavy metal
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uptake into the plant tissue during their metabolic processes (Cuypers et al. 2013). Using hyper accumulator plants
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during phytoremediation method enables to provide more productive results. The reason to use those plants is that they
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are able to accumulate 50 to 500 times more metal in their tissues.
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Phytoremediation processes take different kind of names depending on the pollutants, levels of pollution and
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plant species (Padmavathiamma and Li, 2007). Phytoremediation is a technique which uses plants to cleanup organic
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and inorganic pollutants from the contaminated soil, water and air.
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The names of the methods differ in terms of pollutant types and contaminated areas (soil-air or water), such as
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rhizofiltration, phytodegradation, phytoextraction, phytovolatilization, phytostabilization and rhizodegradation.
75 Phytoextraction (also called phytoaccumulation) is used to remove metal pollutants leading to soil
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contamination through plant roots. A plant used for phytoextraction is required to accumulate a high amount of metal,
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grow rapidly, be deep-rooted, be easily harvested and to have a high tolerance towards heavy metal. In that manner,
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we used, canola (Brassica napus) and soybean (Glycine max) plants which were preferred regarding their properties
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such as oil ratio, efficiency, industrial value, irrigation and fertilizer etc. Those plants are growing rapidly and having
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high biomass and oil in their seed.
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However, the most significant problem after phytoextraction is that the hyperaccumulator plants are identified
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as secondary pollutants because of containing an excessive amount of heavy metals in its tissues and have been
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classified as hazardous waste. Phytoremediation technique contributes huge quantities of contaminated materials to
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the environment and creates further pollution problems (Mohanty, 2016). That is why, phytoremediation technologies
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are usually not considered as final removal methods. Subsequently, an additional treatment such as composting,
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compacting, incineration, pyrolysis and direct disposal are applied to the contaminated plant biomass after
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phytoextraction. Composting and compaction terms are defined as pre-treatment processes causing biomass to be still
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classified as hazardous waste (Sas-Nowosielska et al. 2004). However the incineration process causes air pollution.
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Pyrolysis, on the other hand, is a cost-intensive method which has infrequently been applied in many countries.
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Due to these negative feedbacks written above, a new method is required for the metal recovery from biomass
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classified as hazardous waste, containing heavy metals. The important point; metal recovery from plant waste, instead
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of direct disposal of the harvested plant, is more applicable and economically importance option. In this study, recovery
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of the heavy metals in biomass through electrochemical method is investigated as an alternative to other methods.
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Electrochemical treatment, which is one of the promising methods in recent years, has some features such as recovery
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of metals, low cost, simple operation, slight amount of chemical usage and combination with other treatment processes
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(Ait Ahmed, et al. 2016; Chen, 2004).
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Some researchers have combined electrokinetic method with phytoremediation to remove residual
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contamination and succeed to have cleaner soil in the field. Jiang, et al. (2015) have pursued a radical approach to
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solve the problem of eliminating the plant biomass by thermo-chemically converting renewable energy, and they have
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designed a metal recovery process from waste biomass.
102 Chirakkara et al. (2015) examined on combining an electrokinetic remediation with phytoremediation for a
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soil co-contaminated with heavy metals and PAHs. They had grown oat plant and sunflower in the electro-kinetic cell
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for 30 days. The results showed that the heavy metals and organic pollutants in the soil were significantly reduced.
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However, biomass production of the plants increased with the application of electric current, but there was no
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significant improvement in heavy metal phytoextraction or PAH degradation.
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Mao et al. (2016) examined the processes of coupled electro-kinetic phytoremediation of polluted soils to
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remove Pb, As and Cs. They showed that the solubility and bioavailability of Pb, As and Cs were significantly
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enhanced by the electro-kinetic field (EKF). The electro-kinetic field treatment was efficient in lowering soil pH near
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to the anode which is beneficial for the dissolution of metals. The bioaccumulation of Pb, As and Cs were all increased
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upon EKF treatment, indicating the EKF treatment might have been a good alternative for increasing phytoextraction
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efficiency of Pb, As and Cs.
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However, this study is completely different from the studies mentioned above, in which electro-kinetic
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method and phytoremediation are combined. The aim of this study is to recover heavy metals from waste plants
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obtained electrochemically after phytoextraction. In this study, electrolysis reactions were used for metal recovery and
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toxic metals were recovered in biomass by the electro-reduction method. Electrochemical reduction brought originality
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to the study as it enabled the recovery of metals with high economic value. It also provided a treatment of the biomass,
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containing toxic metals by the “zero waste” principle.
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First, canola (Brassica napus) and soybean (Glycine max) plants were cultivated in multi heavy metal (Cd,
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Pb and Zn) contaminated soil for phytoextraction. Afterwards, the accumulated heavy metals in biomass were turned
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into ionic form through microwave extraction and then converted into metallic form through electrochemical reduction.
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This integrated study has shown that biomass within the scope of hazardous waste can be treated and included in the
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non-hazardous waste class after phytoextraction.
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2. Material and Method
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2.1. Soil and Plant Materials
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In this study, the coordinates of both contaminated (Cd, Pb and Zn) and uncontaminated soil samples were
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determined with Global Positioning System (GPS). The soil contaminated with multi-metal and the one
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uncontaminated were collected from 0-30 cm depth in Kayseri-Incesu (38° 42' 43" N and 35° 15' 55" E) and Copurlu
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Village, located on the way to Mersin-Gözne (36° 87' 32" N and 34° 56''50" N), respectively. The study areas were
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shown in Figure 2.1.
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Figure 2.1. Soil sampling areas
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Canola and soybean plants were grown under controlled environment conditions (50-60% humidity, 16 h of
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light and 8 h of dark photoperiod, 25±2oC temperature and 1500 Lux light intensity) in the climate chamber for 3
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months. Ten canola and 10 soybean seeds were planted in pots during the experiment. All of the plants were irrigated
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regularly and the water-holding capacity of the soil was stabilized at approximately 70% (under field conditions).
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The soil contaminated with higher multi-metal concentration was mixed with the one uncontaminated as 0%
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(controlled clean soil), 25%, 50%, 75% and 100% proportions. Canola and soybean plants were grown in the obtained
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five soil mixtures. The experimental plan was designed with randomized block method in three replicates.
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2.2. Soil and Plant Analyses
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The soil samples were air dried at the room temperature and then sieved from 4 mm sieve for pot experiments.
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For some, physical and chemical analyzes, soil samples were used which passed through a 2 mm. Soil samples were analyzed for pH in a 1:1 (m:v) ratio of soil to water solution, the soil texture was determined
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according to the hydrometer method, the organic matter by modified Walkley–Black titrations and lime by the
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calcimeter method. Total metal analysis of the soil was conducted in compliance with the EPA 3051A method and
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concentrations of the metals were detected with the Agillent brand 7500ce model ICP-MS (Inductively Coupled
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Plasma Mass Spectrometer) (USEPA, 1995b). The accuracy of the method was tested with a standard soil certified
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(CRM 7003). Some physical and chemical properties of the soil, regarded as both contaminated and uncontaminated,
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and initial metal contents were detected. The values determined by Ciftçi (2016) are shown in Table 2.1.
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Table 2.1. Some physical and chemical properties and standard deviations of the uncontaminated and
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contaminated soil samples (n=3) (Çiftçi, 2016)
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As seen in Table 2.1, pH of the soil was moderate alkaline at 8.0. The texture classification of the soil was
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sandy loam. Lime amount was moderate (7.26) while the amount of organic matter was high (5.27). Whereas the total
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amount of nitrogen (N) was considerably higher, available amounts of phosphor (P) (11.34) and potassium (19.55)
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were also high. According to Kabata Pendias, the critical values for Cd, Pb and Zn were between 3-8, 100-400 and 70-
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100, respectively (Kabata-Pendias, 2007).
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According to EPA Method 3051A (USEPA, 1995b), in contaminated soil, total concentrations of Cd, Pb and
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Zn were determined as 483.70 25755.60 and 13412.20 mg kg-1, respectively. On the other hand, the concentrations of
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Cd, Pb and Zn were determined as 1.92; 92.41 and 19.09 mg kg-1, respectively in uncontaminated soil.
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Canola and soybean were used in the pot experiment as plant materials. After harvesting green parts of the
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canola and soybean with the highest phytoextraction capacity during the trial, the moisture contents were measured
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according to Equation (1) after being kept in a drying oven at 70 °C for 72 h (Kaçar, 1984). All the data obtained from
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the plant material during the research were described as oven dry plant biomass at 70°C.
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𝑀𝑜𝑖𝑠𝑡𝑢𝑟𝑒 𝐶𝑜𝑛𝑡𝑒𝑛𝑡
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ℎ
(1)
Harvested canola and soybeans were grinded and solubilized in the microwave oven for 45 minutes with 0.2 g, of
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which is 2 mL deionized water, 2 mL with 35% H2O2 and 4 mL with 65% HNO3.The heavy metal concentration (Cd,
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Pb, Zn) of plant samples were determined by ICP-MS. The accuracy of the analysis was controlled with a standard
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certificate plant (CRM 1573A-tomato leaf) sample. The concentrations of Cd, Pb and Zn were determined as 0.980,
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1.840 and 84.860 mg kg-1, respectively in the standard certified plant sample. Cadmium, Pb and Zn concentrations on
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CRM 1573A-tomato leaf were 0.978, 1.846 and 85.000 mg kg-1, respectively. As can be seen in the results, both values
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were close to each other.
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2.3. Electrochemical Experimental Setup
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Batch electrochemical tests were carried out in an electrochemical glass cell, which was divided into two with
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a permeable filter. For the electrochemical reduction, platinum anode (electrode surface 2 cm2) and Pb cathode
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(electrode surface 2 cm2) were used. A power supply was used in order to provide the constant current during
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electrochemical reduction. The voltage was held stable for each run with a retention time for 2 h.
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2.4. Determination of the Effect of Incineration Temperature on Dry Mass Extraction of toxic metals in the waste of biomass is important and dissolution process is carried out after
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incineration method. For this purpose, 1 g of the grinded plant samples was weighed and put into porcelain crucibles.
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In order to determine the effect of the incineration temperature on dry mass loss and metal solubility, plants were
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incinerated in the ash furnace for 8 h at 105°C, 205°C, 305°C, 405°C and 505°C, respectively. Plant samples required
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for electrochemical tests were incinerated at 505 °C in the ash furnace because the maximum metal solubility was
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achieved at this temperature.
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2.5. Determination of the Effect of Extraction Methods on Metals Solubility
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Two different methods were used to extract the metal accumulated in the biomasses. The chemical extraction
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method was compared with the microwave method in terms of extracting Cd, Pb and Zn concentrations. In order to
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transfer the Cd, Pb and Zn accumulated by canola and soybean into the solution, a chemical extraction was performed
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with 0.2 M HCl solution. After the incineration temperature is determined, 1 g plant sample incinerated at 505 °C was
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solubilized in hot plate with 100 mL of 0.2 M HCl for 2 h.
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For the other extraction method, 1 g of the plant sample was digested in 5 mL of deionized water, 5 mL of 35% H2O2
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and 10 mL of 65% HNO3 for 45 minutes in microwave at 150 °C and pressure of 200 psi. After cooling, the solutions
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were completed up to 100 mL final volume with distilled water and passed through a 0.45 μm filter. Then, the total
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heavy metal concentrations were determined by ICP-MS.
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2.6. Electrochemical Reduction Experiments
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Optimum reduction potentials of Cd, Pb and Zn ions were determined in Cyclic Voltammetry by the addition
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of standard solution, which was containing 25 mg L-1 Cd, Pb and Zn (titrisol) in 50 mL of control plants extracted with
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0.2 M HCI before starting the electrochemical reduction processes. After the optimization processes, during which
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the reduction potential was identified, electrochemical removal efficiencies of Cd, Pb and Zn were determined in the
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microwave extracting solution from canola and soybean biomass. The electrochemical reduction process in the
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solutions was conducted at -0.6 V electrode potential.
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Electrodeposition processes in microwave extracting solutions were realized during 2 h by taking 0.5 mL
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solution from the electrochemical cell at regular intervals (0, 15, 30, 45, 60, 90 and 120 min) at constant voltage. The
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electrochemical removal efficiency (ERE) of Cd, Pb and Zn in the cell,depending on time, were calculated in Equation
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(2), where Co is the initial metal ion concentration (mg L-1) in biomass solution and Ce is equilibrium metal ion
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concentration in treated solution at any time (mg L-1).
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𝐸𝑅𝐸 %
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(2)
2.7. Statistical Analysis
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The interaction between temperature (T), dry mass (DM) and solubility of metal ions was performed for canola and
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soybean using the statistical package Statistical Product and Service Solutions (SPSS) 17.0 for Window. The methods
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included one-way analysis of variance (ANOVA) and linear regression analysis. Duncan's multiple range test was used
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to determine the statistical significance (p< 0.05).
3. Results and Discussion
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3.2. Total Metal Concentrations of Plants
In this study, a soil sample with higher metal concentration was mixed with the uncontaminated soil samples
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as 0% (controlled clean soil), 25%, 50%, 75% and 100%.
The overall picture in the pre-harvest of the grown canola and soybean in soil mixtures are shown in Figure
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3.1a-b. The green parts of the canola (shoot) and soybean grown in contaminated soil (100%) were used as plant
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material and the used materials were also shown with arrow marks.
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Figure 3.1. Overall picture of the pre-harvest a) canola (Brassica napus) and b) soybean (Glycine max)
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plants in the soil mixtures used for experimental studies (Left to right 0% (controlled and clean soil), 25%, 50%, 75%
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and 100% polluted)
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in microwave, were compared with the normal and critical concentrations of Cd, Pb and Zn in plants according to
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Kabata-Pendias, (Table 3.1). It was observed that both plants accumulate metal ions in shoots. As can also be seen in
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Table 3.1, Cd, Pb and Zn concentrations, especially in the shoots of the canola were considerably higher than those of
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the normal concentration, threshold value and critical concentration value.
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Evaluated in terms of total Cd, Pb, Zn concentrations, canola accumulated 5 times more Cd, 7 times more Pb
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and 3 times more Zn than that of soybeans. On the other hand, when evaluating total Cd, Pb and Zn concentrations in
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terms of hyperaccumulation threshold limit, it was seen that the soybean plant accumulated 2.4 times more Cd and the
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canola plant accumulated 11 times more Cd and 3.6 times more Pb.
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251 252 Table 3.1. Initial total multi-metal concentration within the shoot of soybean and canola, normal and critical
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concentration range and hyperaccumulation threshold value of the plant (Kabata-Pendias, 2007; Baker and Brooks,
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1989).
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Hyperaccumulator plants are described as the type of plants, which can include more than 100 mg kg-1 Cd,
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1000 mg kg-1 Pb and 10.000 mg kg-1 Zn (Baker and Brooks, 1989). According to this definition, canola is
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hyperaccumulator in terms of accumulated Cd (1134 mg kg-1) and Pb (3682 mg kg-1) concentration while soybean is
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defined hyperaccumulator in terms of Cd (238 mg kg-1). The success of the phytoextraction method depends on the
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plant biomass production and the ability to uptake high amounts of metals in plant shoots (USEPA, 1995a).
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3.3. Effects of Incineration Temperature on Biomass
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In the evaluation of wastes of plant, pre-treatment at high temperatures leads to mass reduction, which is
265
important for the disposal of waste after phytoextraction and phytomining.
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To determine the effect of incineration temperature on dry mass, dry masses of soybean and canola incinerated
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for 8 h in ash furnace at 105°C, 205°C, 305°C, 405°C and 505°C, respectively. The absolute moisture content (105°C)
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was determined as 2.4% and 12.34% of soybean and canola, respectively. The significant difference is about the
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tolerance shown towards increased Cd, Pb and Zn concentrations of the canola and soybean within the soil, which was
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shown in Figure 3.1. Whereas soybean was drying (necrosis) in accordance with the increasing dosage, canola
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continued to grow showing tolerance to metals. One of the reasons for this situation might be the fact that canola holds
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more humidity. Figure 3.2 shows the effect of the incineration temperature on the dry mass.
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Figure 3.2. Effect of temperature on dry masses of canola and soybean plant
278 The overall accepted temperature for incineration of plant materials was 450°C. Because evaporation losses
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at these temperatures were low in general and it was sufficient for the complete oxidation of the organic substance. It
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has been reported by Hoenig (1995) that temperatures as high as 520 °C do not cause losses of volatile elements such
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as Cd, Pb or Zn, if the programmed temperature curve is sufficiently low in the ash furnace (Hoenig et al., 1995).
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Therefore, the maximum temperature of the study was chosen as 505°C.
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As it was shown in Figure 3.2, green parts of both plants decreased significantly with temperature increase.
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According to linear regression between the dry mass of canola and the T, it seen that there is a very strong positive
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correlation between two parameters (r=0.96) and this relationship was found to be a high significance as statistically
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(0.001< p<0.01). According to simple linear regression between the dry mass of soybean and the T, there is a very
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strong positive correlation between two parameters (r=0.97) and this relationship was found to be a significance as
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statistically (0.001
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With a theoretical calculation, considering that decrease, performed at 505°C for 1 ton of plants, biomasses
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of canola is going to scale down as 214.8 kg and soybean as 127.9 kg. This means that canola, which is accumulating
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more metal, is more effective compared to soybean in terms of phytomining. As the mass of the plants, which was
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considered as waste after phytoextraction, decreases, the application of pre-treatment methods such as incineration
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method was in the foreground. The incineration method also reduces the cost of treatment and the transportation to the
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landfill. However, a substantial amount of contaminants can still be in the ash even after the incineration process. In
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this study, recovery of the metals from the residual ash was provided after incineration and solubilizing, consecutively.
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3.4. The Effect of Extraction Methods on Metals Solubility
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In the evaluation of the products after phytoextraction, the applied extraction process for transferring Cd, Pb
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and Zn from plants to the solution was very significant. Acid extraction (dissolution) is applied mostly through the
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method of incineration methods in order to extract toxic metals from plants after phytoextraction (Zarcinas et al. 2007).
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During metal extractions from organic matrix like plants; hydrofluoric acid (HF), hydrochloric acid (HCI), nitric acid
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(HNO3), perchloric acid (HCIO4) and sulphuric acid (H2SO4) are used individually or in mixtures (Idera et al., 2014).
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Before electrochemical reduction process, Cd, Pb and Zn concentrations transferred from waste plant
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materials (biomass) into the solution are important. In order to determine the concentration of metal ions, biomasses
307
were incinerated by keeping in the ash furnace for 8 h at 105 °C, 205°C, 305°C, 405°C and 505°C, respectively, and
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then extracted with 0.2 M HCI. Total metal concentrations in canola and soybean after the acid extraction process were
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shown in Figure 3.3a-b.
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According to linear regression analysis between the solubility of Cd, Pb and Zn in the canola biomass and the
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T, there is a very strong correlation between the two parameters (r =0.92, 0.87 and 0.93) and this relationship was
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found to be borderline significance as statistically (0.05
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Figure 3.3. Effect of temperature and 0.2 M HCI on metal concentration; a) extracted from canola and b) extracted
315
from soybean
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According to linear regression between the solubility of Cd in the soybean biomass and the T, there is a very
318
strong positive correlation between two parameters (r=0.96) and this relationship was found to be a significance as
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statistically (0.001
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there is a very strong positive correlation between two parameters (r =0.99) and this relationship was found to be a
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very high as statistically (p<0.001). However, in the statistical analysis for Zn, it seen that there is a weak correlation
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between the two parameters (r =0.73) and this relationship was found to be insignificant as statistically (p>0.1).
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The Cd, Pb and Zn concentrations of samples incinerated in the ash furnace at 505 °C and then extracted with
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0.2 M HCI was compared with the performed microwave method results in same samples. Total metal concentration
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of the solubilized from waste of plants through two different methods were shown in Table 3.2.
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Table 3.2. Total metal concentration of solubilized from canola and soybean plants, both through ash furnace and
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microwave methods (mg kg-1)
When the table was examined, it can be seen that the solubilized metal amount with ash furnace was less than
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that of the microwave method.
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After ash furnace method, the percentages of extracted Cd, Pb and Zn from canola and soybean were found
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as 16%, 1% and 8% and 13%, 14% and 11%, respectively. Effectiveness of chemical reagent during metal extraction
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changed depending on initial metal concentration, pollutant types, extraction properties and experimental conditions
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(Hoenig et al. 1995). Since initial metal concentrations in the soybean plant are lower than that of canola, the percentage
337
of extraction obtained from the soybean was higher than the canola. Metal concentrations of the plant samples digested
338
in the microwave were found higher than that of those conducted with ash furnace. Thus, the plant solution extracted
339
with the microwave method was used in the electrochemical reduction tests.
There are limited numbers of studies in literature, in which the about of evaluation of wastes of plant after
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phytoextraction.
Yıldırım (2016) stated in her study, which was conducted for the evaluation of metals in safflower and castor
343
oil plants, that Cd, Pb and Zn concentration extracted with 1.0 M H2SO4 was higher than that of with 0.5 M H2SO4.
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However, the researcher indicated that Cd, Pb and Zn concentration transmitted into solution after extraction was
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unable to reach the total metal concentration extracted through the microwave method (Yıldırım, 2016). For this reason,
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it was one of the most important conditions that the toxic metals in the biomass were passed to the solution in high
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percentages.
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Hetland et al. (2001) utilized chelating agents (EDTA and N-(2-acetamido) iminodiacetic acid) for the purpose
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of recovery of the Pb from harvested biomass after phytoremediation. Researchers were able to extract 98.5% of Pb
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with EDTA at pH 4.5 after two series of washing. They reduced the Pb concentration from 2000 mg kg-1 to 30 mg kg-
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hazardous waste after the extraction (Hetland et al. 2001).
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after liquid extraction from residual biomass. Thus, the plant biomass, initially defined as hazardous waste, was not
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Ginneken et al. (2007) used phytoextraction method in Belgium for the treatment of the soils contaminated
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with heavy metals. Besides, they used plant biomass obtained after phytoextraction for anaerobic decomposition,
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incineration, gasification and the biodiesel produced from seed. The grain or seed of the canola plant used in this study
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could be utilized as raw material for biodiesel production (Ginneken et al., 2007). Many biodiesel types, which are
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considerably used today, are produced from the oils of edible plants such as canola, soybean and sunflower (Silitonga
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et al. 2015).
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According to Jiang et al. (2015) recycling of metals is critical to the sustainability of industrial development,
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as natural reserves are depleting. However, despite the increased demand, none of the resources have been backed by
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recycling, as the recovery of low metal concentrations is costly compared to conventional mining. The recovery of the
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elements may be lower than the cost of disposal of potentially toxic biomass in large quantities. The market value of
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the element for the recovery of biomass heavy metals is quite determinative. In such an application, metal recovery
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values are reduced from the plant's planting and maintenance costs (Jiang et al. 2015).
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3.5. Electrochemical Removal of Metal Ions Transferred to Solution and Effect of Contact Time on Metal
367
Recovery
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The harvested canola and soybean plants were grinded and solubilized by the microwave method and the
370
electrochemical reduction solution was prepared. After the initial metal concentrations (Ce) of the prepared solution
371
have been determined, Electrochemical reduction tests were performed in a 150 mL of the solution at -0.6 V electrode
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potential depending on time. Initial metal concentrations (Ce) in the solution obtained from biomass of canola and
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soybean with the microwave method for Cd, Pb and Zn were determined as 1134, 3682 and 6169 mg L-1 and 238, 554
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and 2380 mg L-1, respectively.
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The change of metal ions concentrations with electrochemical removal tests were shown in Figure 3.4a-b. As
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it is shown in Figure; Cd, Pb and Zn concentrations reduced homogeneously in the whole solution.
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Figure 3.4. Time-dependent change of metal ions concentration at -0,6 V electrode potential in the extracted solution
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from plants; a) electrochemical removal of metal ions in the solution obtained from biomass of canola b)
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electrochemical removal of metal ions in the solution obtained from biomass of soybean
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Electrochemical removal efficiencies measured in accordance with the initial metal concentration for biomass
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of canola and soybean were shown in Figure 3.5a-b.
In the first 30 minutes; Cd, Pb and Zn were removed by about 91%, 97% and 41%, respectively, in the
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electrochemical cell from the solution of canola biomass. At the end of 2 h, the removal efficiencies were calculated
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97% for Cd, 99% for Pb and 46% for Zn (Fig.3.5a).
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Figure 3.5. Time-dependent change of the removal efficiencies of Cd, Pb and Zn at -0.6 V electrode potential in the
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extracted solution from plants; a) change of electrochemical removal efficiency in the solution obtained from biomass
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of canola b) change of electrochemical removal efficiency in the solution obtained from biomass of soybean
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The removal efficiency in the electrochemical cell with regard to the initial metal concentration in solution of
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soybean biomass was shown in Figure 3.5b. At the end of 2 h, the electrochemical removal efficiencies for Cd, Pb and
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Zn were found 80%, 94% and 68%, respectively.
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The yield of electrochemical metal removal in soybean plant, which has less metal accumulation compared
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to canola, was found to be high. It was concluded that after conducting the first step with high efficiency, the recovery
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of metals was also higher by electrochemical method.
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The findings were compatible with the results of the study by Yıldırım (2016) and Eke (2010), conducted for
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the utilization of safflower (Carthamus tinctorius), castor oil (Ricinus communis) and Ni hyperaccumulator Thlaspi
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elegans Boiss plant after phytoextraction.
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After the electrochemical process, the reduced metal ions from the extraction solution of the canola biomass
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were separated from the surface of the Pb electrode by scraping. The scraped metal was considered as the recovered
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quantity and approximately 0.0048 g of solid material was obtained after electrodeposition. The solid material was
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defined as inert due to its metallic formation. The solid material obtained was dissolved in concentrated HF and 1:3 ratio of HCI and it was determined
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quantitatively by ICP-MS in order to find out whether it includes Cd, Pb and Zn. Since the reduction process takes
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place on the Pb electrode (cathode), Pb concentration was neglected, but Cd and Zn concentration was determined in
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the solution. The transformation of Cd, Pb and Zn ions into electrochemically reduced metallic form after
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phytoextraction, is very important from an environmental point of view. These metals are classified as precious metals
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and quite overpriced (Cd-3750 $ ton-1, Pb-817 $ ton-1 and Zn-1007 $ ton-1). In other words, it will contribute to the
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economy of the country with the electro-recovery process (Robinson et al. 1997).
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This study revealed that extracting toxic metals from the biomass of plants with a decent
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extraction/solvent/acid with maximum efficiency is the most important step in metal recovery. As a result of the high
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extracting of the metal ions from biomass, the maximum recovery can be carried out by electrochemical reduction.
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4. Conclusions
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In this study, a considerable amount of metal removal was provided through electrochemical reduction from
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extracted solutions obtained from canola and soybean biomass. The contamination of soil with more than one metal
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has reduced the phytoextraction yield of plants. It was determined that the soybean was not a suitable plant for
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phytoextraction because the efficiency of phytoextraction in this plant was lower than canola.
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The electrochemical reduction method tested in this study can be defined as a significant method for the
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removal of toxic effect and recover valuable metals. The extraction process conducted by the microwave method was found to be more effective than ash furnace
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method with 0.2 M HCl. The extraction process is very important for the second step (electro-recovery) and more
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studies are required to be conducted to increase the recovery efficiency.
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The implementations of microwave method and following usage of the electrochemical reduction provide
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metal ion removal and metal recovery. The recommended combined method is an alternative advanced technique that
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can be used instead of composting and compaction, combustion and gasification in the assessment of contaminated
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plants.
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Acknowledgements
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This research was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) Project
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No: 115Y337 and the Mersin University Scientific Research Project (MEÜ BAP) Unit with 2017-2-TP2-2579.
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This academic work was linguistically supported by the Mersin Technology Transfer Office Academic Writing Center
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of Mersin University.
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Cuypers A, Remans T, Weyens N, Colpaert J, Vassilev A, Vangronsveld J (2013) Soil–plant relationships of heavy
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Eke M (2010) The study of nickel acid extraction and electrochemical metal recovery from nickel hyperaccumulator
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Thlaspi elegans Boiss. Dissertation, Mersin University
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Ginneken VL, Meers E, Guisson R, Ruttens A, Elst K., Vangronsveld J, Diels L, Dejonghe W (2007) Phytoremediation
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hyperaccumulaor plant Alyssum bertolinii as a potential agent for phytoremediation and phytomining of Nickel. J
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L. oil as feedstock for biodiesel production. Fuel 156:63-70.
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Soil Survey Staff (1951) Soil Survey Manual. US Dept Agr Handbook No:18, US Government Print Office,
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USEPA (1995a). Contaminants and remedial options at select metals-contaminated sites. EPA/540/R-95/512.6. US
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USEPA (1995b.) Test Methods for Evaluation of Solid Waste vol. IA, Laboratory Manual Physical/Chemical Methods,
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SW 846, 40 CFR Parts 403 and 503, 3rd (ed), US Government Printing Office, Washington.
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Yıldırım, D., 2016. The removal/recovery of heavy metals from castor (Ricinus communis) and safflower (Carthamus
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Zarcinas BA, Cartwright B, Spouncer L (1987) Nitric acid digestion and multi-element analysis of plant material by
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Figure 2.1. Soil sampling areas
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Figure 3.1. Overall picture of the pre-harvest a) canola (Brassica napus) and b) soybean (Glycine max) plants in the
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soil mixtures used for experimental studies (Left to right 0% (controlled and clean soil), 25%, and 50%, 75% and 100%
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polluted)
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a)
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Canola (Brassica napus)
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b) Soybean (Glycine max)
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Figure 3.2. Effect of temperature on dry masses of canola and soybean plant (mean ±SD, n=3)
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Figure 3.3. Effect of temperature and 0.2 M HCI on metal concentration; a) extracted from canola and b) extracted
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from soybean (mean ±SD, n=3)
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a)
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Figure 3.4. Time-dependent change of metal ions concentration at -0,6 V electrode potential in the extracted solution
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from plants; a) electrochemical removal of metal ions in the solution obtained from biomass of canola b)
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electrochemical removal of metal ions in the solution obtained from biomass of soybean
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Figure 3.5. Time-dependent change of the removal efficiencies of Cd, Pb and Zn at -0.6 V electrode potential in the
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extracted solution from plants; a) change of electrochemical removal efficiency in the solution obtained from biomass
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of canola b) change of electrochemical removal efficiency in the solution obtained from biomass of soybean
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a)
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Table List
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Table 2.1. Some physical and chemical properties and standard deviations of the uncontaminated and contaminated
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soil samples (n=3) (Çiftçi, 2016) Soil Properties
Uncontaminated
Contaminated
Soil
Soil
References
20.5±1.1
84.6±2.3
Silt (0,002-0,02 mm) (%)
27.0±0.9
8.4±0.5
Clay (<0.002 mm) (%)
52.5±1.0
7.0±0.6
Texture class
C (Clay)
LS (Loamy sand)
pH (in 1:1 saturated soil)
8.23
8.04
Lime (CaCO ) (%)
28.34
7.26
Organic matter (%)
3.04
5.27
Soil Moisture (%)
5.50±0.54
4.69±0.24
Water saturation (%)
60±1.30
28±0,90
Total N (%)
2.24±0.01
2.10±0.01
Kacar, 1995
Available P (mg P2O5 kg-1)
1.98±0.23
11.34±0.25
Olsen et al., 1982
Available K (mg K2O kg-1)
63.4±3.10
19.55±0.15
Richards, 1954
1.92±0.10
483±32.9
USEPA, 1995b
92.4±3.35
13412±0.1
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EPA 3051A- Total Zn (mg/kg)
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EPA 3051A-Total Cd (mg/kg)
Bouyoucos, 1951
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Sand (0.02-2 mm) (%)
3
Soil Survey Staff, 1951
EPA 3051A- Total Pb (mg/kg)
19.1±0.01
25755±0.54
DTPA extractable Cd (mg/kg)
0.05±0.02
26.8±0.16
Lindsay and Norvell,
DTPA extractable Pb (mg/kg)
1.03±0.21
31.1±1.72
1978
DTPA extractable Zn (mg/kg)
0.75±0.33
128±11.6
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Table 3.1. Initial total multi-metal concentration within the shoot of soybean and canola, normal and critical
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concentration range and hyperaccumulation threshold value of the plant (Kabata-Pendias, 2007; Baker and Brooks,
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1989).
Normal
Critical
Hyperaccumulation
mg kg-1 DM*
Concentration
Concentration
Threshold Value
Range, mg kg-1
mg kg-1
DM*
DM*
5-30
100
30-300
1000
Range, mg kg-1 Canola
DM*
Cd
238±1.89
1134±12.3
0.10-2.40
Pb
554±8.16
3682±14.12
0.2-20.00
Zn
2380±12.62
6169±15.83
*DM: Dry Mass
623 624
1-400
100-400
10000
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Table 3.2. Total metal concentration of dissolved canola and soybean plants, both through ash furnace and microwave
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methods (mg kg-1) Application
Cd (mg kg-1)
Pb (mg kg-1)
Ash Furnace
186±0.10
38±0.03
483±0.45
Microwave
1134±10.69
3682±13.37
6169±25.21
Ash Furnace
31±0.34
Microwave
238±0.58
76±0.48
261±0.41
554±1.32
2380±19.50
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Canola
Soybean
Zn (mg kg-1)
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Conflict of Interest and Authorship Conformation Form
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Please check the following as appropriate:
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All authors have participated in (a) conception and design, or analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version.
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This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue.
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The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript
o
The following authors have affiliations with organizations with direct or indirect financial interest in the subject matter discussed in the manuscript:
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Affiliation
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Aydeniz Demir Delil
Mersin University
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Highlights
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Cultivation of canola (Brassica napus) and soybean (Glycine max) plants in contaminated soil with heavy
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metals
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Chemical and microwave extraction exposure of canola and soybean which accumulate heavy metals
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Recovery of heavy metals through electrochemical method from biomass after phytoextraction
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The results of the study show that heavy metals in biomass can be recovered by electrochemically
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