Changes in heavy metal mobility and availability in contaminated wet-land soil remediated using lignin-based poly(acrylic acid)

Accepted Manuscript Title: Changes in heavy metal mobility and availability in contaminated wet-land soil remediated using lignin-based poly(acrylic acid) Authors: Tianqi Zhao, Kun Zhang, Junwei Chen, Xiaobai Shi, Xu Li, Yanli Ma, Guizhen Fang, Shiyu Xu PII: DOI: Reference:

S0304-3894(19)30081-0 https://doi.org/10.1016/j.jhazmat.2019.01.061 HAZMAT 20216

To appear in:

Journal of Hazardous Materials

Received date: Revised date: Accepted date:

24 August 2018 17 December 2018 21 January 2019

Please cite this article as: Zhao T, Zhang K, Chen J, Shi X, Li X, Ma Y, Fang G, Xu S, Changes in heavy metal mobility and availability in contaminated wet-land soil remediated using lignin-based poly(acrylic acid), Journal of Hazardous Materials (2019), https://doi.org/10.1016/j.jhazmat.2019.01.061 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

Title：Changes in heavy metal mobility and availability in contaminated wet-land soil remediated using lignin-based poly(acrylic acid) Zhao Tianqia, Zhang Kuna, Chen Junwei a, Shi Xiaobaia, LI Xua, Ma Yanlia,*, Fang Guizhena,b, Xu Shiyu a

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a. Material Science and Engineering College, Northeast Forestry University Heilongjiang, Harbin 150040, PR China b. Key Laboratory of Bio-based Material Science and Technology Ministry of Education, Northeast Forestry University, Heilongjiang, Harbin 150040, PR China

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Graphical Abstract

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Highlight  LBPAA increased soil remediation efficiency for removal of heavy metal.  LBPAA can sequester heavy metal ions from contaminated soil.  No negative effect on the soil organic matter content, the growth of fungal and bacterial colonies. Abstract To mitigate the serious ecological problems and risks to human health that are posed by heavy metals in the soil, it is important to enhance the efficiency of heavy metal extraction by washing contaminated soil using chemical methods. Secondary pollution of soil by chemical chelating

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agents has, however, brought a new threat to the environment. Here, we describe a biodegradable LBPAA (lignin based poly(acrylic acid)) composite that was designed as a chelating agent to wash soil contaminated with Cu2+, Zn2+, Cd2+ and Pb2+ ions. Extraction and ion transfer of heavy metal ions by the LBPAA composite improved the remediation rate of contaminated soil during water leaching. After washing five times, the LBPAA-assisted elution process reduced the amount of Cu2+, Zn2+, Cd2+ and Pb2 ions in contaminated soil to 22.57%, 52.60%, 13.63% and 17.95%, respectively. These values are 2.39-fold, 5.04-fold, 5.04-fold and 1.31-fold, respectively, better than elution with deionized water. Additionally, LBPAA is able to sequester Cd2+ and Pb2+ ions from the contaminated soil and transfer them to the eluent. In summary, this work provides a safe, environmentally friendly and sustainable remediation strategy for heavy metal-contaminated soil and demonstrates a new application for lignin in the field of soil remediation.

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1. Introduction

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Rapid industrialization of the manufacture of batteries, automotive pigments, film, coatings and steel, together with improper storage and disposal of waste electrical and electronic equipment, has led to heavy metal-contaminated wastewater [1, 2]. Heavy metals can cause a lot of diseases. Pb can cause severe dysfunction in the kidneys, liver and reproductive system. Cd can cause high blood pressure, kidney damage, and destruction of testicular tissue, osteoporosis and destruction of red blood cells. Cu can cause vomiting, diarrhea, stomach cramps, and nausea, or even death.[3] The accumulation of Zn in soil will result in uneven emergence of wheat, less tillers, dwarf plants and yellowing leaves. Excessive zinc also inactivates the soil and reducing the number of bacteria in the soil [4-6]. Soil contamination causes immense ecological damage and poses a real threat to human health[7]. Currently, soil remediation is carried out using mechanical or chemical methods, such as burying, evaporation, dispersion and washing [8]. Many chemical remediation methods, which would offer short treatment times and minimal dispersion of contaminants, have been considered to enhance soil washing. These include chemical precipitation, electrochemical treatment, electrodialysis, circulation-enhanced electro-kinetics, evaporation recovery, solvent extraction, ultrafiltration, ion exchange, metal redox treatment, membrane reverse osmosis, adsorption, microbial electrochemical system, biological filtration and phytoremediation [9-11]. Inexpensive chelating agents are widely recognized to provide a convenient and effective method for the purification of heavy metal-contaminated soil, such as clays, agricultural wastes, biomass, coconut shell and sewage sludge biochar [12, 13]. Heavy metals can strongly associate with organic matter in the soil and much research has focused on using chemical chelating agents to reduce levels of heavy metal ions in the soil and thus reduce the uptake of these toxic metals by crops [14, 15]. The use of chemical remediation agents, such as reducing agents (sodium oxalate, ascorbic acid, hydroxylamine hydrochloride and sodium disulfate), oxidants (hydrogen peroxide and persulfate), acids, bases and surfactants that enhance heavy metal desorption from soils, is, however, harmful to microorganism in soil. To overcome this problem, biosorption and biomass-derived adsorbents have been extensively studied over the past decades. One of these methods, phytoremediation using hyperaccumulating plants, is both time-consuming and of limited effectiveness [16]. The concept of biomass-derived adsorbents, using biomaterials [17], such as plant matter, agricultural waste [9] and marine organisms, is based

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on the presence of reactive groups similar to those found in conventional chelating agents or in vitro ion exchange resins. Stabilization and solidification is considered to be the most effective remediation method for heavy metal-contaminated soil [18]. The stable solidification of heavy metals by adsorbents is, however, easily destroyed by soil biodegradation and diffusion of metal ions, resulting in secondary pollution [19]. Another challenge is that the presence of other metal cations (Na+, K+, Ca2+, etc.) in the soil reduces the effectiveness of adsorbents for remediation of heavy metal-contaminated soils. Although soil washing is an effective method for remediation, the disposal of heavy metal-containing washing liquor and the impact on the soil must be carefully considered [7, 16]. In the past, soil washing for rehabilitation of heavy metal-contaminated soil has been carried out using dynamic redox, surfactants, minerals, chelating agents, organic acids, inorganic acids and alkali solutions. Chelating agents, such as EDTA/phosphoric acid/oxalic acid and [S,S]-ethylene-diamine-disuccinic-acid (EDDS), have been shown to promote dissolution of residual heavy metals in soil [20]. The use of ultrasound combined with acidic soil washing has been shown to be a very satisfactory method for the removal of heavy metals from soils [21]. All of the methods described above are, however, harmful to soil microbes. After washing with chelating agent, the redistribution of heavy metals in soil were often used as safe index[22]. In addition to the physical and chemical properties of soil, soil enzyme activity can be used as a representative evaluation index of remediation performance [23], since residual metals and washing solutions may alter substrates, protein active groups or enzyme-substrate complexes in soils. Biochar is now commonly used for fixing heavy metals in contaminated soils [4, 5]. Biochar can cost-effectively stabilize pollutants, sequester carbon and improve soil quality through nutrient recharge, water conservation and enhancement of enzyme and microbial activity. For example, the high pH and high Fe and Al oxide/oxyhydroxide content of red mud make it an effective remediation agent for heavy metal-contaminated soil and addition of red mud to contaminated soil increased bacterial activity. Phenylpropane structural units are connected by C-C bond and ether bonds to form three-dimensional network structure of lignin in plants. We designed and synthesized LBPAA, which called Lignin based poly(acrylic acid), that prepared by grafting and free radical copolymerization of both acrylic acid and lignin. In a previous study, When LBPAA was buried in soil, the soil organic matter and number of bacterial colonies were restored to normal levels after approximately 35 days [24]. The lignin is used as reactive fillers to support the hydrogel’s volume when LBPAA hydrogel is applied to absorption under the stress condition of salt ions and micro-strain. In this study, yellow soil from Hunan was chosen as the experimental soil. LBPAA is used as an adsorbent to removal heavy metal ion in soil that the network structure was designed by the volume-supported principle of lignin fragment. We assessed and demonstrated its significant effects on the mechanical properties of LBPAA composite hydrogels and the remediation process of heavy metal ions (Cu2+, Pb2+, Cd2+ and Zn2+ ions) contaminated soils in soil systems. We examined the effect of LBPAA microgel on degradation behavior, soil remediation efficiency, immobilization performance and migration of heavy metals. With the assistance of rain or irrigation water, LBPAA has the potential to be a safe, environmentally friendly and sustainable soil remediation agent. Our work here represents a new strategy to develop applications of lignin in the field of agriculture for remediation of heavy metal-contaminated soil.

2. Experimental 2.1 General material characteristics

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The morphology of porous LBPAAs was characterized by SEM using Quanta 200 (FEI Ltd., USA). The samples were gold-coated before scanning to provide an electrically conductive surface for better imaging.The FTIR spectra were recorded on solid in KBr pellets by spectrometer (Nicolet 6700, Thermo Scientific Inc., USA) connected to software with the OMNIC operating system (Version 9.0). The 13C NMR spectra were tested by solid NMR using Bruker ultrashield 500 plus (Bruker, GER) with tetra-methyl silane (TMS) as the internal standard. XRD analysis was determined by XRD-6100 (Shimadzu, JPN). The compressive modulus of LBPAA and PAA hydrogels was determined by a stress-controlled rheometer using TA2000EX (TA Instruments, USA) [25]. The hydrogels were prepared into cylinder molds (25 mm diameter × 3 mm height).

2.2 Materials and instrumentation

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Wheat straw-derived alkali lignin, containing 82.69% lignin, 8.35% carbohydrates, and 8.96% ash was obtained from Tralin Paper Co., Ltd. (Shandong, China). After removal of sugars and ashes, the purified lignin contained phenolic hydroxyl groups (1.49 mmol∙g-1) and aliphatic hydroxyl groups (1.46 mmol∙g-1). The weight average molecular weight of the purified lignin was 1903 Da [24]. All the reagents were purchased by Aladdin Chemistry Co., Ltd., Shanghai, China. Lignin (1.10 g) was dissolved in NaOH (1.25 M, 85 mL) and mixed with N, N-methylene-bisacrylamide (0.97 g), then added APS (0.10 g) and the flask was sealed at 60 ℃ for 10 min, then got lignin grafted with N, N’-methylene-bisacrylamide (LM) [26]. Ammonium persulfate (0.26 g), LM (1.09 g) and acrylic acid (AA, 63% (w/w) in water, 1.56 mL) were added and the mixture was sealed in a flask under a nitrogen atmosphere. The mixture was copolymerized at 60 ℃ for 4 h and then freeze dried to provide the LBPAA composite [24, 27]. Soil samples were collected from Changsha in Hunan Province, China (location 28° 11′ 49′′ N and 112° 58′ 42′′ E). The soil was air-dried, homogenized, and passed through a 0.83 mm sieve before analysis. The soil was principally contaminated by dipping and aging with Cu2+, Zn2+, Cd2+ and Pb2+ ions (8.56, 14.89, 10.03 and 9.41 mg kg-1, respectively). The soil pH was 7, as measured at a soil-to-water ratio of 1:5. The amount of heavy metals (Cu, Zn, Cd and Pb) in the soil, eluent and LBPAA was determined by aqueous extraction, using the HNO3 digestion process [6]. A TAS-990 atomic adsorption spectrophotometer (Purkinje General Instrument Co., Ltd., Beijing, China) was used to quantify heavy metal ions.

2.3Deionized water-assisted soil remediation The remediation method is based on the principle that the affinity of Pb2+ for LBPAA is higher than its affinity for water. Different mixtures of saturated LBPAA hydrogel and soil were prepared which mass ratios are 0:100, 1:100, 10:100, 50:100 and 100:100 separately, and the total weight of the mixture is 200 g. The composition of LBPAA was 60 wt% PAA and 40 wt% LM hydrogel, with an equilibrium water absorption capacity of 411.9 g g-1. The soil and LBPAA mixtures were saturated with deionized water (200 mL) for 6 h, and

then loaded onto a column with a 4 cm pad of degreasing cotton at the top and bottom. An additional 200 mL of deionized water was used for loading the column, draining and obtaining a soil remediation column. The column was then rinsed five times with deionized water (200 mL). The eluents were collected separately in volumetric flasks and diluted with deionized water to 500 mL. The amount of eluted heavy metal ions in each sample was determined by atomic absorption spectrophotometry [28].

2.4 Migration behavior of heavy metals

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A series of soil remediation columns were rinsed with deionized water (200 mL). The eluates were collected and made up to 500 mL in volumetric flasks. Samples of LBPAA (0.2 g) and soil (0.2 g) were collected from the top of the columns, a quarter way down, half way down, three quarter way down and from the bottom of the columns to determine the amount of heavy metals. The metal contents were determined using atomic absorption spectrometry (AAS) [14].

2.5 Interference by cationic salts

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Apart from that, the adsorption and swelling properties of LBPAA composite are significantly reduced by cation interference[19], which causes the composite hydrogel network to shrink, locking in heavy metal ions. During the elution of particulates in the soil with water, the gel is gradually degraded into small particles by abrasion, and washed far away from the cultivation layer. To determine the effect of cationic salts on the heavy metal carrying capacity of the eluent, + K and Ca2+ ions were used to interfere with the process of soil remediation by the LBPAA composite. A series of soil remediation columns were prepared using the method described in Section 2.2.1. Five different eluents were used for the interference experiments: deionized water, KNO3 (0.125 M), Ca(NO3)2 (0.125 M), KNO3 (0.25 M) and Ca(NO3)2 (0.25 M). The removal of Cu2+, Zn2+, Cd2+ and Pb2+ ions by the eluent and the degree of soil remediation were determined using the method described in Section 2.3. Polyester filter cloth bags, with a pore size of 25 μm, were placed at top of the gel soil remediation column, a quarter way down, half way down, three quarter way down and at the bottom of the column. Average values were used to determine the effect of interference by cationic salts on the ability of the LBPAA composite to remove heavy metals.

2.6 Soil characteristics

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As described previously [24], the amounts of organic matter and clay and the number of colonies in the soil were chosen as indicators of soil performance in the LBPAA remediation process [29]. Preparation of the pretreatment soil sample and specific test conditions are described in our previous paper [24]. Two different growth media were used to culture soil microorganisms for determination of colony numbers since soil contains both fungi and bacteria. Containmented soil were collected and air-dried. Organic matter content was determined using the oxidation method of K2Cr2O7-H2SO4. Briefly, the organic matter content was calculated by oxidizer consumption. The value of clay content was calculated by the proportion of soil Particles with a diameter <2 μm. The soil samples were suspended in 1 mL distilled water to isolate microorganism. Using a super-clean bench, soil suspension (125 μL) was added to the liquid medium of beef cream agar

(for bacteria) and potato (for fungi), respectively and sealed at 25 °C for 24 h. The number of colonies was then counted using an Icount 30 D automatic colony counter (Shineseo Technology Co. Ltd., HangZhou, China).

3. Results and discussion 3.1 General material characteristics of LBPAA 13

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C-NMR spectra show that LBPAA was synthesized by radical copolymerization of lignin grafted MBAm as a macromonomer with acrylic acid. The signal at 175 ppm for the formation of carbonyl ester (C=O-O-R) is the evidence of the occurrence of esterification (Figure S3). Apart from that, the signals (Figure S3) around 60 and 160 ppm are the characteristic signals of a phenyl propane unit. [14] In addition, the signal at 72 ppm is attributed to C-β in intermolecular linkage of β-O-4, indicating that the LBPAA consists of lignin. The FTIR exhibits the functional groups of PAA, lignin-MBAm and LBPAA hydrogels (Figure S4). The stretching vibration of O−C=O bonds (signal at 1720 cm-1) is another evidence of radical copolymerization between lignin grafted MBAm and acrylic acid. A new C−N stretching band appears at∼1450 cm-1, confirming the presence of amide groups. Also, two deformation vibration peaks at 1250 and 1050 cm-1 are attributed to the phenolic hydroxyl groups and hydroxyl groups for PAA. The guaiacyl breathing vibration appears at ∼1030 cm-1, the syringe breathing vibration appears at ∼834 cm-1, and broad benzene ring breathing vibrations in the range of at 1600∼1450 cm-1, indicating that lignin-MBAm cross-linked PAA to form network successfully. [14] It is consistent with the analysis of NMR spectra. From figure 1a, when the  was fixed at 6.283 rad/s and measure temperature is at 25℃, after balanced by the deionized water, the G’ and G’’ data of LBPAA hydrogel are inferior to PAA at the lower strain range (< 1%). After the strain exceed 1%, the G’ and G’’ data of LBPAA hydrogel are higher than PAA hydrogel. Also, for freeze-dried samples, the G’ and G’’ data of LBPAA are superior to PAA hydrogel at the lower strain range (< 3%). With the increasing of strain from 0.1% to 100%, the G’ and G’’ data of LBPAA hydrogel declined markedly from 72.93kPa to 0.1 kPa. But the G’ and G’’ data of PAA maintain at 5 kPa when the strain is blow 23%. After that, the G’ and G’’ data of PAA also decreased rapidly. After balanced by the deionized water, water balance capacity of LBPAA (60 PAA/40 LM) hydrogels is 411.9 g·g-1 while the PAA's capacity is g·g-1. From figure 1b, the G’ and G’’ data of

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LBPAA are similar to PAA at the  range from 0 to 150 rad/s. Freeze-dried PAA sample is higher than others sample. In addition, it can be seen from Figure 1c, there is no junction point of G' and G'' data of LBPAA and PAA whether balanced by deionized water or not, indicating the crosslinking reaction has been almost accomplished in the process of preparation of LBPAA and PAA. Finally, from Figure 1d, after balanced by the deionized water, the G’ data of LBPAA is closed to PAA. Furthermore, the G’ data of water balanced LBPAA is higher than freeze-dried PAA at temperature range of 25 to 35℃. Until test temperature beyond 35 ℃, the G’ value of water balanced LBPAA and PAA are similar to freeze-dried LBPAA, and those are still lower than freeze-dried PAA. It is noteworthy that, the G’ and G’’ of water balanced LBPAA are higher than water balanced PAA when the strain exceed 1%. That of water balanced LBPAA are also slight superior to water balanced PAA at temperature range of 25 to 35℃. We draw a conclusion that the mechanical properties of water balanced LBPAA was better than water balanced PAA.

3.2 Remediation of heavy metal-contaminated soil by LBPAA

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To clarify the migration path of heavy metals, we determined the effect of different ratios of LBPAA to soil over five rinses. The highest amount of heavy metals eluted per kilogram of soil was achieved with an LBPAA: soil ratio of 10:100. Specific details are as follows: Cu2+ ions, 3.089 mg kg−1 soil, leaching rate 36.09%; Zn2+ ions, 2.221 mg kg−1 soil, leaching rate 14.92%; Cd2+ ions, 5.276 mg kg−1 soil, leaching rate 52.60%; Pb2+ ions, 5.893 mg kg−1 soil, elution rate 62.62%. In all cases, the amount of heavy metal eluted was higher than from blank samples. We accumulate the 5 times of heavy metal ion data in eluent in figure S2. Obviously, we can directly draw the conclusion that the heavy metal amount of eluent which the ratio of LBPAA to contaminated soil is 10:100 (w/w) is higher than other ratios. Therefore, only 10:100 (w/w) LBPAA to contaminated soil is adopted in all experiment.

3.3Heavy metal migration behavior

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To demonstrate the contribution of LBPAA to the remediation of contaminated soil, LBPAA was mixed with contaminated soil in a ratio of 10:100 (w/w). The effect of remediation on soil levels of Cu2+, Zn2+, Cd2+ and Pb2+ ions is shown in Figure 2. After five rinses, the amount of Cu2+ ions in the soil decreased from 29.16% to 22.57% (Figure 2a), whereas the amount of residual Cu2+ ions in control soil was 67.62%. The amount of Zn2+ ions in the soil decreased from 58.83% to 52.6% (Figure 2b). This result is consistent with the conclusion that the rate of removal of Zn2+ ions by the eluent is lower. The amount of residual Zn 2+ ions in control soil was 90.59%. The amount of Cd2+ ions in the soil decreased from 42.85% to 13.63% (Figure 2c), and the amount of residual Cd2+ ions in control soil was 47.40%. The amount of residual Pb2+ in the soil decreased from 58.3% to 17.95% (Figure 2d), and the amount of residual Pb2+ ions in control soil residual was 37.48%. These results demonstrate that LBPAA improves the efficiency of soil remediation by facilitating removal of heavy metal ions [30]. With LBPAA-assisted remediation, the amount of Zn2+ ions in the eluent was < 10.5% (Figure 2b) whereas the control eluent removed 9.41% of Zn2+ ions (Figure 1). With LBPAA-assisted remediation, the eluent contained < 10% Cu2+ ions, 49.85% Cd2+ ions and 53.13% Pb2+ ions. The values in control eluent were 32.38%, 52.60% and 62.52%, respectively. These findings suggest that LBPAA does not make a significant contribution to the removal of heavy metals in the elution process. In summary, the heavy metal content in soil and eluent decreased in the presence of LBPAA, indicating that LBPAA has excellent absorption properties for Cu2+, Cd2+ and Pb2+ ions. We also observed that the amount of Cu2+ ions on the LBPAA composite was maintained at 69%. LBPAA has excellent adsorption properties for Cu2+ ions because of the unoccupied outer orbitals. It is noteworthy that the residual amount of Cd2+ ions on the LBPAA composite decreased to 36.52% and that of Pb2+ ions decreased to 28.92%. The findings from these studies suggest that LBPAA plays a role in the transfer and adsorption of heavy metal ions from the soil to the eluent during the remediation of Cd2+ and Pb2+ ions. The retention of Zn2+ ions by the LBPAA composite is ~ 36–38%. In contrast, we found that LBPAA acts as an adsorbent during remediation of Zn2+ ions. The leaching rate of heavy metal ions (Figure 2) improved as the ratio of ionic radius to hydrated ionic radius increased (Table 1). During the remediation process, heavy metal ions with a

3.4 Interference behavior of K+ and Ca2+ ions in LBPAA remediation

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large effective hydrated radius become trapped in small pores in the soil and are difficult to rinse out with water. The spatial resistance of the hydrated metal ions is a thus a key factor in determining the elution rate of heavy metal ions. The outer electron orbitals of Zn2+, Cd2+and Pb2+ ions are fully occupied (Table 1) and the ionic hydration enthalpy decreases with increasing ionic radius. Cu2+ ions, however, do not follow this pattern. Cu2+ ions have the smallest ionic radius but the highest ionic hydration enthalpy because they have unoccupied outer orbitals. Also, we summarized the studies assessing the effect of adsorbent on the remedy process of heavy metal ion contaminated soil in Table S2.

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The swelling capacity of LBPAA in deionized water is more than 400 g/g that is inconvenient to washing experiment because of larger volume. Furthermore, dilute acid solution is often used for the removal of heavy metal ions as an eluent. However, hydrogel network of LBPAA (Lignin based poly acrylic acid) has dramatic shrinkage in acid, which enhance the mass transfer resistance of heavy metal ions from the hydrogel. Apart from that, in our precious research, salt concentration, charge valence and ionic radius of external salt solution greatly influenced the swelling behavior of the superabsorbents. (Figure S1) [14] Salt ion can interfere with heavy metals adsorption of LBPAA, and reduce the adsorption capacity of heavy metal ions. [22] Here, we used potassium nitrate and calcium nitrate to imitate cations in the soil when soaking the saturated adsorbed heavy metal ions onto LBPAA (Figure 3). The adsorption capacity of LBPAA for the four heavy metals ions was markedly decreased by ionic stress. Potassium nitrate (0.25 M) had the largest effect on the adsorption capacity for heavy metals ions, whereas calcium nitrate had almost no effect on the adsorption capacity for heavy metals ions, except for Zn2+ ions. Ionic stress interferes very little with the adsorption of copper ions by LBPAA because of strong chelation. In contrast, there is significant interference with the adsorption of Cd2+ and Pb2+ ions, which are easily removed by the eluent. Potassium nitrate (0.25 M) is thus an inexpensive detergent that could be used with LBPAA for the elution of heavy metal ions.

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3.5 Characteristics of contaminated soil

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In our previous study [24], when LBPAA was buried in soil in a closed system for 180 days, the best recovery period for colonies of microorganisms and organic matter was found to be 35 days, whereas the clay content continued to gradually decrease. Here, the organic matter content, clay content, and numbers of fungal and bacterial colonies were used as indicators to investigate the interference by ions on soil properties. As shown in Figure 4, the use of salt solutions, rather than deionized water, as the eluent had a significant effect on the characteristic properties of the soil. Comparing salt solutions with deionized water, there was no significant change in the organic matter content of contaminated soil (Figure 4a), although Ca2+ ions (0.125 M and 0.25 M) did slightly reduce the amount of organic matter. Both K+ and Ca2+ ions had a significant effect on the clay content of contaminated soil (Figure 4b). The interference was highest in soil contaminated with Cd2+ ions, and interference was also noticeable in soil contaminated with Pb2+ ions. The situation is different for soils contaminated with either Cu2+ or Zn2+ ions. Here, interference by cations causes an initial sharp increase in clay content, following by a trend towards a decrease. It is probable that Cu2+ and Zn2+ ions increase aggregation of clay particles in the soil in the early stage of leaching. Afterwards, as the number of rinses increased, the clay content of the soil

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declined because of the decrease in contaminating ions in the soil. With interference by cations, the soil clay content in Pb2+ ion-contaminated soil fell, but the clay content did not decrease with the rinsing process. It is noteworthy that the 0.25 M Ca2+ solution has the smallest interference on soil clay content. The two most common types of microorganism in soil are fungi and bacteria. The growth status of these two types of microorganism during soil remediation are shown in Figures 4c and 4d. Pollution with Pb2+ ions had little effect on the growth of soil fungi (Figure 4c). The growth of fungi in soils contaminated with Cu2+ or Cd 2+ ions was slightly enhanced by K+ and Ca2+ ions[31]. The number of fungal colonies was noticeably increased in soil treated with 0.125 M K+ solution. In contrast, soil treated with Ca2+ ion solutions had markedly increased bacterial growth, compared with the blank sample (Figure 4d). Growth of bacteria in the soil was significantly inhibited by all heavy metal ions (Cu2+, Zn2+, Cd2+ and Pb2+ ions). However, bacterial growth can be improved in Pb2+ contaminated soil by 0.25 M K+ solution, with the largest number of bacterial colonies seen at the 5th soil remediation of Pb2+ ions. It can, therefore, be considered that the growth of bacterial colonies in the soil are not affected by 0.25 M K+ solution or Ca2+ solution. In summary, 0.25 M Ca2+ solution had no significant effect on soil organic matter content or numbers of soil microorganisms. The clay content of the soil was, however, affected by Ca2+ ions. We found that fungal species appears to have higher tolerance to above heavy metal toxicity in comparison with bacterial[29].

3.6 Interference behavior of K+ and Ca2+ on elution with water

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To determine the effect on leaching of using salt solutions instead of water as the eluent, we used the solutions of potassium nitrate and calcium nitrate described above as the eluent. The removal of heavy metals from a soil column with an LBPAA: soil ratio of 10:100 (w/w) is shown in Figure 5. The salt solutions decreased the leaching efficiency of heavy metals. The absolute value of Cu2+ ions eluted by brine from contaminated soil is minimal. This discrepancy may be attributable to the deswelling effect of salt solutions on the LBPAA composite, which blocks the diffusion channels used by Cu2+ ions. By the same principle, the removal of Zn2+, Cd2+ and Pb2+ ions were significantly decreased. These results indicate that ionic salt solutions are not suitable for use as eluents.

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4. Conclusions

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The adsorption of Cu2+, Zn2+, Cd2+ and Pb2+ ions by LBPAA composite was investigated as a way to improve heavy metal removal for soil remediation. Notably, LBPAA was found to be a potential carrier, with the ability to sequester Cu2+ ions during the soil remediate process. Additionally, LBPAA was able to remove Cd2+ and Pb2+ ions from the contaminated soil and transfer them to the eluent. The deswelling effect of cations on the hydrogel can be used as an inexpensive detergent to help invalid LBPAA composite reuse. Although elution with cation-containing solutions had no negative effect on the soil organic matter content or the growth of fungal and bacterial colonies, the rate of removal of heavy metals in the LBPAA elution process was reduced, apparently because of cation interference with the LBPAA composite. Salt solutions are thus not suitable as eluents for in situ soil remediation.

References [1] B. Sharma, S. Singh, N.J. Siddiqi, Biomedical Implications of Heavy Metals Induced Imbalances in Redox Systems, BioMed Research International, 2014 (2014) 640754. [2] T. Ghnaya, M. Mnassri, R. Ghabriche, M. Wali, C. Poschenrieder, S. Lutts, C. Abdelly,

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Nodulation by Sinorhizobium meliloti originated from a mining soil alleviates Cd toxicity and increases Cd-phytoextraction in Medicago sativa L, Frontiers in Plant Science, 6 (2015) 863.

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[3] E.N. Zare, A. Motahari, M. Sillanpää, Nanoadsorbents based on conducting polymer

nanocomposites with main focus on polyaniline and its derivatives for removal of heavy metal

U

ions/dyes: A review, Environmental Research, 162 (2018) 173-195.

N

[4] K. Lu, X. Yang, G. Gielen, N. Bolan, Y.S. Ok, N.K. Niazi, S. Xu, G. Yuan, X. Chen, X. Zhang,

A

D. Liu, Z. Song, X. Liu, H. Wang, Effect of bamboo and rice straw biochars on the mobility and

M

redistribution of heavy metals (Cd, Cu, Pb and Zn) in contaminated soil, Journal of

ED

Environmental Management, 186 (2017) 285-292. [5] J. Liang, Z. Yang, L. Tang, G. Zeng, M. Yu, X. Li, H. Wu, Y. Qian, X. Li, Y. Luo, Changes in

PT

heavy metal mobility and availability from contaminated wetland soil remediated with

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combined biochar-compost, Chemosphere, 181 (2017) 281-288. [6] R. Zhou, X. Liu, L. Luo, Y. Zhou, J. Wei, A. Chen, L. Tang, H. Wu, Y. Deng, F. Zhang, Y. Wang, Remediation of Cu, Pb, Zn and Cd-contaminated agricultural soil using a combined red

A

mud and compost amendment, International Biodeterioration & Biodegradation, 118 (2017) 73-81. [7] C. Feng, S. Zhang, L. Li, G. Wang, X. Xu, T. Li, Q. Zhong, Feasibility of four wastes to remove heavy metals from contaminated soils, Journal of Environmental Management, 212

(2018) 258-265. [8] N. Das, P. Chandran, Microbial Degradation of Petroleum Hydrocarbon Contaminants: An Overview, Biotechnology Research International, 2011 (2011) 941810. [9] Y. Zhang, J. Zhao, Z. Jiang, D. Shan, Y. Lu, Biosorption of Fe(II) and Mn(II) Ions from

IP T

Aqueous Solution by Rice Husk Ash, BioMed Research International, 2014 (2014) 973095. [10] J.-H. Chang, Y.-L. Wang, S.-Y. Shen, A specific configuration of circulation-enhanced

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electrokinetics (CEEK) to remediate real-site Cd and Pb contaminated soils, Journal of Hazardous Materials, 359 (2018) 408-413.

U

[11] H. Wei, M. Huang, G. Quan, J. Zhang, Z. Liu, R. Ma, Turn bane into a boon: Application of

N

invasive plant species to remedy soil cadmium contamination, Chemosphere, 210 (2018)

A

1013-1020.

M

[12] M.I.S. Gonzaga, C. Mackowiak, A. Quintão de Almeida, A. Wisniewski, D. Figueiredo de

ED

Souza, I. da Silva Lima, A. Nascimento de Jesus, Assessing biochar applications and repeated Brassica juncea L. production cycles to remediate Cu contaminated soil,

PT

Chemosphere, 201 (2018) 278-285.

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[13] M.M. Lakouraj, F. Mojerlou, E.N. Zare, Nanogel and superparamagnetic nanocomposite based on sodium alginate for sorption of heavy metal ions, Carbohydr Polym, 106 (2014) 34-41.

A

[14] X. Guo, G. Zhao, G. Zhang, Q. He, Z. Wei, W. Zheng, T. Qian, Q. Wu, Effect of mixed chelators of EDTA, GLDA, and citric acid on bioavailability of residual heavy metals in soils and soil properties, Chemosphere, 209 (2018) 776-782. [15] M.Z.u. Rehman, M. Rizwan, A. Hussain, M. Saqib, S. Ali, M.I. Sohail, M. Shafiq, F. Hafeez,

Alleviation of cadmium (Cd) toxicity and minimizing its uptake in wheat (Triticum aestivum) by using organic carbon sources in Cd-spiked soil, Environmental Pollution, 241 (2018) 557-565. [16] M.Z.u. Rehman, M. Rizwan, S. Ali, Y.S. Ok, W. Ishaque, Saifullah, M.F. Nawaz, F. Akmal, M. Waqar, Remediation of heavy metal contaminated soils by using Solanum nigrum: A review,

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Ecotoxicology and Environmental Safety, 143 (2017) 236-248. [17] N. Mahfoudhi, S. Boufi, Nanocellulose as a novel nanostructured adsorbent for

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environmental remediation: a review, Cellulose, 24 (2017) 1171-1197.

[18] M. Taubert, S. Stöckel, P. Geesink, S. Girnus, N. Jehmlich, M. von Bergen, P. Rösch, J.

N

ecosystem function, Environmental microbiology, (2017).

U

Popp, K. Küsel, Tracking active groundwater microbes with D2 O labeling to understand their

A

[19] Y. Ma, Y. Sun, Y. Fu, G. Fang, X. Yan, Z. Guo, Swelling behaviors of porous lignin based

M

poly (acrylic acid), Chemosphere, 163 (2016) 610-619.

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[20] J. Beiyuan, D.C.W. Tsang, M. Valix, W. Zhang, X. Yang, Y.S. Ok, X.-D. Li, Selective dissolution followed by EDDS washing of an e-waste contaminated soil: Extraction efficiency,

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fate of residual metals, and impact on soil environment, Chemosphere, 166 (2017) 489-496.

CC E

[21] B. Park, Y. Son, Ultrasonic and mechanical soil washing processes for the removal of heavy metals from soils, Ultrasonics Sonochemistry, 35 (2017) 640-645. [22] J. Beiyuan, Y.M. Awad, F. Beckers, D.C.W. Tsang, Y.S. Ok, J. Rinklebe, Mobility and

A

phytoavailability of As and Pb in a contaminated soil using pine sawdust biochar under systematic change of redox conditions, Chemosphere, 178 (2017) 110-118. [23] J. Im, K. Yang, E.H. Jho, K. Nam, Effect of different soil washing solutions on bioavailability of residual arsenic in soils and soil properties, Chemosphere, 138 (2015)

253-258. [24] Y. Ma, Y. Sun, Y. Fu, G. Fang, X. Yan, Z. Guo, Swelling behaviors of porous lignin based poly (acrylic acid), Chemosphere, 163 (2016) 610-619. [25] A.L.Z. Lee, Z.X. Voo, W. Chin, R.J. Ono, C. Yang, S. Gao, J.L. Hedrick, Y.Y. Yang,

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Injectable coacervate hydrogel for delivery of anticancer drug-loaded nanoparticles in vivo, ACS applied materials & interfaces, (2018).

SC R

[26] E.N. Zare, M.M. Lakouraj, N. Kasirian, Development of effective nano-biosorbent based on poly m-phenylenediamine grafted dextrin for removal of Pb (II) and methylene blue from

U

water, Carbohydrate Polymers, 201 (2018) 539-548.

N

[27] Y. Ma, L. Lv, Y. Guo, Y. Fu, Q. Shao, T. Wu, S. Guo, K. Sun, X. Guo, E.K. Wujcik, Z. Guo,

A

Porous lignin based poly (acrylic acid)/organo-montmorillonite nanocomposites: Swelling

M

behaviors and rapid removal of Pb (II) ions, Polymer, 128 (2017) 12-23.

ED

[28] D.L. Hughes, A. Afsar, D.M. Laventine, E.J. Shaw, L.M. Harwood, M.E. Hodson, Metal removal from soil leachates using DTPA-functionalised maghemite nanoparticles, a potential

PT

soil washing technology, Chemosphere, 209 (2018) 480-488.

CC E

[29] W. Xue, D. Huang, G. Zeng, J. Wan, M. Cheng, C. Zhang, C. Hu, J. Li, Performance and toxicity assessment of nanoscale zero valent iron particles in the remediation of contaminated soil: A review, Chemosphere, 210 (2018) 1145-1156.

A

[30] M. Cao, S. Tu, S. Xiong, H. Zhou, J. Chen, X. Lu, EDDS enhanced PCB degradation and heavy metals stabilization in co-contaminated soils by ZVI under aerobic condition, Journal of Hazardous Materials, 358 (2018) 265-272. [31] Y. Ma, X. Li, H. Mao, B. Wang, P. Wang, Remediation of hydrocarbon–heavy metal

co-contaminated soil by electrokinetics combined with biostimulation, Chemical Engineering Journal, 353 (2018) 410-418. [32] H.P. Lu, Z.A. Li, G. Gascó, A. Méndez, Y. Shen, J. Paz-Ferreiro, Use of magnetic biochars for the immobilization of heavy metals in a multi-contaminated soil, Science of The Total

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Environment, 622-623 (2018) 892-899. [33] D. Tica, M. Udovic, D. Lestan, Immobilization of potentially toxic metals using different soil

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amendments, Chemosphere, 85 (2011) 577-583.

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Figure

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Figure 1 G' and G" of LBPAA and PAA (a) on strain (with  of 6.283 rad/s at 25℃), (b) on frequency (with strain of 0.5％at 25℃), (c) on time (with  of 6.283 rad/s, strain of 0.5％ at 25℃), (d) on temperature (with  of 6.283 rad/s, strain of 0.5％)

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Figure 2. Effect of LBPAA hydogel: soil ratio on amount of heavy metals (Cu2+, Zn2+, Cd2+, Pb2+) extracted from contaminated soil.

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Figure 3 Distribution of heavy metal ions of Cu2+, Zn2+, Cd2+and Pb2+.

Figure 4 Interference of K+ and Ca2+ ions in LBPAA remediation.

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Figure 5 Interference of K+ and Ca2+ for the characteristics of contaminated soil.

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Figure 6 Interference by K+ and Ca2+ on elution with water

Table 1 Hydration of metal ions with different ionic radii and hydrated ion energies [27-29]

Zn2+

Ionic radius /(nm) 0.074

0.43

Ratio of ionic radius to hydrated ionic radius 0.1721

Cu2+

0.073

0.207

Cd2+

0.097

Pb2+

0.132

Effective radius of hydrated ion/(nm)

Ionic hydration enthalpy /(kJ·mol-1)

Configuration of electrons

2046

1𝑠 2 2𝑠 2 2𝑝6 3𝑠 2 3𝑝6 3𝑑10

0.3527

2100

0.231

0.4199

1807

0.266

0.4962

1481

1𝑠 2 2𝑠 2 2𝑝6 3𝑠 2 3𝑝6 3𝑑9 1𝑠 2 2𝑠 2 2𝑝6 3𝑠 2 3𝑝6 3𝑑10 4𝑠 2 4𝑝6 4𝑑10 1𝑠 2 2𝑠 2 2𝑝6 3𝑠 2 3𝑝6 3𝑑10 4𝑠 2 4𝑝6 4𝑑10 4𝑓14 5𝑠 2 5𝑝6 5𝑑10 6𝑠 2

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Ion property (anion: NO3-)