A new efficient indigenous material for simultaneous removal of fluoride and inorganic arsenic species from groundwater

A new efficient indigenous material for simultaneous removal of fluoride and inorganic arsenic species from groundwater

Accepted Manuscript Title: A new efficient indigenous material for simultaneous removal of fluoride and inorganic arsenic species from groundwater Aut...

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Accepted Manuscript Title: A new efficient indigenous material for simultaneous removal of fluoride and inorganic arsenic species from groundwater Authors: Tasneem Gul Kazi, Kapil Dev Brahman, Jameel Ahmed Baig, Hassan Imran Afridi PII: DOI: Reference:

S0304-3894(18)30431-X https://doi.org/10.1016/j.jhazmat.2018.05.069 HAZMAT 19436

To appear in:

Journal of Hazardous Materials

Received date: Revised date: Accepted date:

26-1-2018 28-5-2018 31-5-2018

Please cite this article as: Kazi TG, Brahman KD, Baig JA, Afridi HI, A new efficient indigenous material for simultaneous removal of fluoride and inorganic arsenic species from groundwater, Journal of Hazardous Materials (2018), https://doi.org/10.1016/j.jhazmat.2018.05.069 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.

A new efficient indigenous material for simultaneous removal of fluoride and inorganic arsenic species from groundwater Tasneem Gul Kazi*, Kapil Dev Brahman, Jameel Ahmed Baig, Hassan Imran Afridi, National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080,

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Tasneem Gul Kazi, (Corresponding author)* e-mail [email protected] Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080.tel:+92-22 2771379; fax: +92- 22-

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2771560.

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Kapil Dev Brahman, e-mail [email protected], Center of Excellence in Analytical

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Chemistry, University of Sindh, Jamshoro 76080.tel:+92-22-2771379; fax:+92- 22-2771560

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Jameel Ahmed Baig, e-mail [email protected], Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro 76080.tel:+92-22 2771379; fax: +92- 22-2771560.

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Hassan Imran Afridi, e-mail [email protected], Center of Excellence in Analytical

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Chemistry, University of Sindh, Jamshoro76080.tel:+92-22-2771379. fax:+92- 22-2771560.

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Graphical abstract

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Highlights: 

Simultaneously removal of fluoride and inorganic arsenic species in underground water.



SEM and FTIR studies indicated the sorption of fluoride and arsenic species occurred.



Effects of different parameters on the biosorption capacity of sorbates on peel of



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C. pubescens. Kinetic and isotherm sorption study were done in order to design large scale removal of these toxicants. 

Thermodynamic calculation specified the process of sorption was exothermic and spontaneous.

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Abstract

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The contaminated groundwater is one of emerging environmental issue in Pakistan and

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biosorbent considered to be the best alternative to improve the quality of groundwater. Thus, an

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indigenous biosorbent, Cucumis pubescens (peel of fruit) has been carried out efficiently for simultaneous removal of arsenic species and fluoride from groundwater. The characterization of

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bio-sorbent for removal of As species (AsIII, AsV) and F- was studied by FTIR spectroscopy and

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SEM. Batch experiments were carried out for the optimization of adsorption capacity at different

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parameters such as pH (3–11), concentration of biosorbates (100–500 µg/L) for As species and F- ion), biosorbent dose (2– 6 g/L), contact time (10–60 min) and temperature (303-323 K). The

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influence of common ions was also investigated. The different biosorption isotherms were applied to determine the most appropriate equilibrium curves for the removal/biosorption of As

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species and F- by a biosorbents. The mean sorption energy calculated from Dubinin– Radushkevich model, indicated chemisorptions phenomena. Thermodynamic parameters indicated the biosorption phenomena of AsIII, AsV and F- ions were spontaneous and exothermic. The removal study of study analytes indicated that the sorption kinetics based on pseudo-secondorder equation. 2

Keywords: Arsenic species, fluoride, biosorption capacity, isotherms, thermodynamics 1. Introduction Arsenic and fluoride (As and F-) are contaminated groundwater, which affected large

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populations at global levels, especially in Bangladesh, Canada, China, India, Mexico, United States and Pakistan (Zhu et al. 2006; Bagla and Kaiser 1996; Thornburg and Sahai 2004; Brahman et al. 2013a; b; Baig et al. 2009; Arain et al. 2009). The high levels of F-, AsIII and AsV are considered as hazardous to the environment (Zhu et al. 2006; Bagla and Kaiser 1996;

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Thornburg and Sahai 2004; Brahman et al. 2013a,b; Baig et al. 2009; Arain et al. 2009). The low

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level of F- is an essential component for the health of dental and bones of mammals, but as a

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double-edged sword, the excessive intake through food and drinking water may cause chronic

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diseases such as mottling of teeth, skeletal fluorosis and neurological damage (Rafique et al. 2008; Brahman et al. 2014). However, drinking water is a major source of daily intake of

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F- (Saralakumari and Rao 1993). The As has been known as one of the most toxic substance

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since long but recently its increasing role as a contaminant of water has gained the attention of researchers throughout the world (Niu et al. 2007). Intake of As can lead to disturbance of the

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pulmonary functions, cardiovascular and nervous system functions, and increases the risk of

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cancers in skin, lungs, liver, kidney, and bladder (Wadhwa et al. 2011; Arain et al. 2009). As and F-contamination in the water has occurred through two different sources i.e.,

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natural and anthropogenic. These are encountered in minerals and in geochemical deposits, which are generally released into subsoil water sources by the slow natural degradation of containing rocks (Banerjee et al. 2008; Daifullah et al. 2007). The removal of F- and As have been studied, such as chemical precipitation (Camacho et al. 2009; Turner et al. 2005), ion exchange (Ishihara et al. 2009; Kim and Benjamin 2004), 3

adsorption (Manning et al. 2002), membrane (Tor 2007), electrolysis (Wang et al. 2003), coagulation (Hu et al. 2005) and lime treatment (Schmidt et al. 2009). Some of these methods have disadvantages, such as cost-effective and produced secondary toxic sludge, which requires

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further treatments. Among all of these methods, adsorption has been recognized as an effective technique for the treatment of F- and As-contaminated water. Many materials can be used as adsorbents, such as activated carbon (Jang et al. 2008), chitosan (Boddu et al. 2008; Viswanathan et al. 2009), alumina (Kim et al. 2004), fixed bed packed with granular calcite (Yang et al. 1999), fly ash (Piekos and Paslawska 1999), and bone char (Chen et al. 2008;

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Medellin-Castillo et al. 200). However, some adsorbents are efficient only at high F- ion

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concentrations (Fan et al. 2003), while others are really expensive (like activated carbon). In

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addition, As contamination is often accompanied with F- in practical cases. The existing

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adsorbents can only adsorb As or F- separately. So, it is necessary to investigate cost-effective adsorbent that can efficiently adsorb both F- and As (either AsIII or AsV) simultaneously.

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The aims and objectives of current studies are: (i) to find out the removal efficiency of

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AsIII, AsV, and F- simultaneously from aqueous media onto an indigenous biosorbent, peel of

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Cucumis pubescens, (ii) to study the effects of different adsorption parameters such as pH, sorbates concentration, biosorbent dosage, contact time and temperature for the removal of AsIII,

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AsV and F-, (iii) the characterization of proposed biosorbent before and after adsorption, (vi) to evaluate adsorption capacity of the biosorbent for AsIII, AsV and F- under equilibrium

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experimental conditions using different isotherms, kinetics and thermodynamics models and (v) the real application of proposed biosorbent for the remediation of AsIII, AsV and F- in groundwater from As and F- endemic area of Pakistan (Tharparkar). 2. Materials and methods

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2.1 Chemicals and Instruments Ultrapure water obtained from ELGA lab water system (Bucks, UK) was used throughout the work. All chemicals and reagents were of analytical grade, Merck (Darmstadt, Germany).

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The stock standard solution of As (III) at a concentration of 1000 mg/L was prepared by dissolving As2O3 in 1M KOH and adjusting the pH to 7.0 with 50% HCl. Working standard solutions were prepared by stepwise diluting the stock solutions just before use. While the working standard solutions for total As were prepared by dilution of certified standard solution (1000 mg/L) in 0.2M HNO3. Triton X-114 (Sigma) was used as the non-ionic surfactant. While

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0.1% (w/v) Ammonium-pyrrolidine-dithiocarbamate (APDC) and Titanium (IV) dioxide were

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utilized as sorbents for AsIII and iAs respectively. The pH of the sample solution was adjusted

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with 0.1M HCl/0.1M NaOH. All the glassware were kept overnight in 5M HNO3, rinsed twice

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with deionized water before used.

Mechanical shaker (Gallankamp, England) was used for shaking. pH was measured by a

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pH meter (781-pH meter, Metrohm). Ion meter 781 Metrohm (Herisau, Switzerland) with ion

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selective electrode (ISE, Metrohm) employed for F- determination. A double beam Perkins-

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Elmer atomic absorption spectrometer model 700 (Norwalk, CT, USA) equipped with deuterium lamp back corrector, graphite furnace HGA-400 and an autosampler AS-800 was used. Mixed

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solutions of Mg(NO3)2 (Merck, Darmstadt, Germany) and Pd (Aldrich, Milwaukee, WI, USA) were used as a chemical modifier. The operating parameters of As hollow cathode lamp were set

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as recommended by the manufacturer and reported in previous work (Baig et al. 2009;Brahman et al. 2014). For the characterization of biosorbent, its particle size and biosorption activity were determined by Laser scattering particle size distribution analyzer, model LA-300 (Horiba Scientific, Kyoto, Japan), Scanning Electron Microscope (SEM) (JEOL model JSM-6380) and

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Thermo Nicolet 5700 FTIR spectrometer (Thermo Nicolet Analytical Instruments, Madison, WI) respectively. 2.2 Biosorbent collection and preparation

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The indigenous fruit Cucumis pubescens was collected from the Thar Desert, the southeast region of Sindh, Pakistan. The peels were separated from the pulp of fruit by stainless steel knife. The peels were washed with tap, distilled and deionized water, separately and peels were spread on plastic trays in the fuming cupboard and allowed to dry at ambient temperature for one week. Afterward, peels were pulverized and heated in an electric oven at 343K for 2 h.

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The dried biomass was sieved in Ro-Tap type electrical sieve shaker and sieved through a nylon-

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fiber sieve to collect mesh size 200 (<75µm), stored in the vacuum desiccators.

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2.3. Batch sorption experiments

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The sieved biomass fruit peel of C. pubescens (100 mg) was taken in replicate six

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conical flasks (50 ml in capacity) and added 20 ml As species [AsIII, AsV] and F- solution having

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concentration in the range of 100 - 500 µg/L and 8.0 - 24 mg/L, respectively. The pH was adjusted in the range of 3 to 11 by adding 0.5 M NaOH or 0.5M HNO3 solutions in different

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flask, at temperature ranged from 303 to 323 K. After shaking at the rate of100 cycles/min for 2h, the solution was separated from the biomass by filtration with Whatman No.42 filter paper.

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The initial and final concentrations of AsIII, AsV, and F- in each flask were determined by AAS

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and ISE, prior and after the biosorption procedure. The As species and F- were determined by solid phase and cloud point extraction methods and ISE as reported in our previous work (Brahman et al. 2013a; Arain et al. 2003). The amount of the sorbates, adsorbed (µg or mg) per unit mass of biosorbent (qe) was calculated by equation (1): 6

𝑞𝑒 =

(𝐶𝑖 − 𝐶𝑒 ) 𝑉 → (1) 𝑚

Where qe is the biosorption capacity, Ci and Ce are the initial and final concentrations of the sorbate (µg/L or mg/L), ‘m’ is dry biomass of peel used as a biosorbent and V is the volume of

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the solution (L).

After optimizing all parameters the effect of interfering ions (Na+, K+, Ca2+, Mg2+, Fe2+, Cl-, Br-, NO3- and SO42-) on biosorption capacity were also determined. Once optimizing the experimental conditions the method was applied on real field underground water samples (n=30), of Diplo (sub-district of Tharparkar), Pakistan. All the experiments were performed in triplicates

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at the desired conditions. The FT-IR and SEM studies of biomass (Peel of C. pubescens) before

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and after loaded of AsIII, AsV and F- were investigated. In FT-IR spectroscopy the samples were

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prepared by mixing 1.0 mg of sample with 99.0 mg of dried, finely powdered potassium bromide

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3. Results and Discussion

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scanned from 4000 to 400 cm−1.

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(KBr) and then condensed in the 13-mm die at a pressure of 6 tons for 5 min. The pellets were

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3.1 Characterization of biosorbent The particle size distribution of fruit’s peel of Cucumis pubescens was found between

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2.27 and 344 μm, while the higher percentage of the biosorbent consists of particles with a diameter in the range of 59 – 133 μm with a mean particle size was 74.8 μm (Fig. 1). It is

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reported that higher adsorption occurs with smaller particles; this may be due to the fact that smaller particles yield large surface areas, which provide more availability of sites for target analytes per unit weight of the biosorbent. Biosorption is a surface phenomenon in which the rate and extent of biosorption are the functions of the specific surface area of the biosorbent. In fact,

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the amount of biosorption per unit weight of biosorbent depends on its composition, texture and porosity (Baig et al. 2009) [6]. 3.1.1 FTIR Study

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FTIR is a useful tool to identify functional groups in a molecule, as each specific chemical bond often has a unique energy of absorption band, which provide information about the presence of different compound responsible for biosorption of F- and As species. The FTIR spectra of As/F- loaded and unloaded biosorbent material are shown in Fig. 2. The FTIR spectrum of unloaded biosorbent (Fig. 2a) indicated the presence of broad and strong peak

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between 3000–3600 cm−1 indicated the overlapping of –OH and –NH2 stretching vibration.

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Other bands at 2919.7 and 2851 cm-1 indicates the-CH and -CH2 stretching vibration, peak at

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1733.4 cm-1 belongs to carbonyl (-C=O ) stretching vibration, -NH bending vibration showed at

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1635 cm-1, peak at 1384 cm-1 showed -CH bending, band at 1246 cm-1 indicate the -C-N

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vibration while peaks at 1162.3 cm-1 and 1061.5 cm-1 showed -CO stretching vibration.

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The FTIR spectra of loaded biosorbent material with F- and As species showed the deformation and shifting of some peaks (Fig. 2b & 2c)( Asadullah et al. 2014) [36]. A major

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difference was observed in the –OH and –NH2 stretching vibration around the wavenumber of

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3418.7 cm−1, which was shifted to 3414.2 cm−1 and 3409.7 cm−1 in the case of biosorption of Fand As, respectively. The –NH2 bending vibration at the wave number 1635.0 cm−1 was also

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shifted to higher frequencies 1652.3 and 1683.3 cm-1 in F- loaded biosorbent (Fig. 2b), while in As loaded biosorbent the frequency shifted to 1647.2 and 1653.9 cm-1 (Fig. 2c). FTIR peak of CN functional group was shifted from 1246.1 to 1241.3 cm−1 by As biosorption while the peak of CO was shifted from 1061.5 to 1057.6 in F- sorbed biosorbent. Hence, based on FT-IR spectrum

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analysis, it can be inferred that the binding of As and F- on the biosorbent (peel of C. pubescens) takes place by the interactions with -NH2 and -CO functional groups. 3.1.2 SEM Study

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The surface morphologies of fruit’s peel of C. pubescens, after loaded with As species, Fand both, were obtained by scanning electron microscopy (Fig. 3). The instrument was operated at a 20kV accelerating voltage and SEM micrographs were taken at ×270 magnifications with a size of 50µm. All the samples were dried and coated with graphite to enhance the electron

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conductivity before analysis. The secondary electron image of these particles showed the rough

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surfaces having large surface area and high porosity, which may increase the biosorption

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capacity (qe) (Basu and Ghosh 2011). The change in morphology of peel of C. pubescens after

was carried out by natural biosorbent.

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3.2 Effect of pH

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As species, F- and both (As species and F-) loading indicated that the biosorption of these ions

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The effect of pH on AsIII, AsV and F- sorption by C. pubescens was studied in the pH range of 3 to 11 at the contact time (2 h), biosorbent dosage (5.0 g/L), shaking frequency 100

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cycles/min, solution volume (20 ml), 303K temperature and with concentrations 100 µg/L, 100

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µg/L and 20 mg/L, respectively. The results were obtained and shown in Fig. 4. AsIII naturally exists in non-ionic (H3AsO3) and anionic (H2AsO3−) forms in the pH range of 2.0–8.0 and 8–12,

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respectively. The qe value of AsIII increases with an increase in pH up to 8.0 and then it decreased by increasing the pH. When the pH of solution >8.0, the negative charges on the surface of biosorbent was occurred, which enhance the repulsive forces between the biosorbent surface and biosorbate, results in biosorption decreased.

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It was reported that AsV at pH range 3 - 6, occurs mainly in the monovalent form (H2AsO4−). However, a small degree of nonionic H3AsO4 also exists at pH 3, so the maximum qe value of AsV on indigenous biosorbent occurred >pH 4.0, because of a high degree of

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protonation. The neutral species of AsV would not interact with a positive surface charge of biosorbent (Ranjan et al. 2009; Ruixia et al. 2002). A further increase in pH caused a decrease in qe value for AsV on the biosorbent, this might be due to change in surface charge of biosorbent from positive to neutral and neutral to negative.

The removal of F- from aqueous media studied at different pH range from pH 3 to 11

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(Fig. 4). It was observed that the % removal of F- was > 90% at pH 3 to 8. Thus, the proposed

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adsorbent is effective for the removal of F- in acidic to a basic aqueous solution. However,

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maximum removal of F- ions observed at pH > 4.0. Then, slightly decreased with an increase of

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pH value 7 (Fig. 4). The biosorption of F- decreases at pH <4, might be due to the existence of F-

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in stable HF form. Whereas pH value > 8.0, the concentration of OH− in solution becomes

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higher, which may compete with the oxyanions of As and F-, leading to the desorption (Ruixia et al. 2002). Thus, for further experiment pH, 7.0 was selected as an optimum pH value, because

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naturally occurring water has pH ≈ 7.0, although the biosorption efficiency of AsV and F- were decreased 2.54% and 5.51%, respectively at pH 7.0.

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3.3 Effect of ions Concentration

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The effect of sorbates concentration was studied by varying concentrations of AsIII (100 -

500 µg/L), AsV (100 - 500 µg/L) and F- (8 to 24 mg/L), separately using 5.0 g/L of biosorbent dosage for 2 h contact time at pH 7.0. The results indicated that the qe values gradually increased with increasing initial concentration of AsIII, AsV and F- up to the range of 100 - 300 µg/L (qe = 15.4 - 25.6 µg/g), 100 - 400 µg/L (qe= 19.2 - 75.5 µg/g) and 8.0 - 16 mg/L (qe= 1.53 - 2.95 10

mg/g), respectively (Fig. 5). At higher concentration of these elements, no effect was seen on qe values, this is due to limited active sites on the biosorbent surface. The lower q e value of AsIII than AsV is due to the more mobility of AsIII (Smedley and Kinniburgh 2002).

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3.4 Effect of Dosage The different contents of selected biosorbent (2 - 6 g/L) were studied under optimum conditions, contact time (2 h), and concentrations of AsIII, AsV, and F- were 300 µg/L, 400 µg/L and 16 mg/L, respectively at pH 7.0, in order to ascertain the effect of dosage on the biosorption of F- and As species. The maximum qe value of biosorbent was obtained as 25.6 µg/g, 75.5 µg/g

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and 2.95 mg/g for AsIII, AsV and F-, respectively (Fig. 6). No significant change in qe value of

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biosorbent was observed up to 5g/L of biosorbent dosage, which showed its large surface area

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available for biosorption of studied ions. Furthermore, the qe value was decreased by increasing

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the biosorbent dosage (> 5 g/L). It is because of intermolecular attraction between biosorbent

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materials increased to lessen the active sites on the surface of biosorbent for bio-sorption (Fig.

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3.5 Kinetic study

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6).

The kinetic studies of biosorption of AsIII, AsV and F- on the fruit’s peel of C. pubescens

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were conducted simultaneously by varying the qe value with respect to time at optimum conditions. The results indicated that sorption is a rapid process and the equilibrium level was

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obtained at 50, 50 and 40 min for AsIII, AsV and F-, respectively. This showed that the biosorption rate is faster for F- than As species. The sorption kinetic arrangement of the ions was analyzed using the Lagergren rate equations 2 and 3:

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𝑘1 log(𝑞𝑒 − 𝑞𝑡 ) = 𝑙𝑜𝑔𝑞𝑒 − ( ) 𝑡 → (2) 𝑃𝑠𝑒𝑢𝑑𝑜 1𝑠𝑡 𝑜𝑟𝑑𝑒𝑟 2.303 𝑡 𝑞𝑡

=𝑘

1 2 2 𝑞𝑒

𝑡

+ 𝑞 → (3) 𝑃𝑠𝑒𝑢𝑑𝑜 2𝑛𝑑 𝑜𝑟𝑑𝑒𝑟 𝑒

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Where, k1 (1/min) and k2 (g/µM min) or (g/mM.min) are the pseudo first and pseudo secondorder rate constants respectively. The qe and qt showed the biosorption capacity values of biosorbent at equilibrium condition at a time “t”, respectively. The pseudo-second-order model showed higher “r2” values for all three ions as compared to the pseudo-first-order model (Table

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1).

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3.6 Isotherm study of biosorption

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Different isotherm models e.g., Langmuir, Freundlich and Dubinin–Radushkevich have

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been studied for describing sorption phenomenon of AsIII, AsV and F-. The study of each isotherm was carried out by varying initial concentrations of AsIII, AsV and F- 100 - 300 µg/L,

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100 - 400 µg/L (and 8.0 - 16 mg/L, respectively at ambient temperature (303 K). 3.6.1 Langmuir sorption isotherm

𝐶𝑒 1 𝐶𝑒 = 0 + 0 → (4) 𝑞𝑒 𝑄 𝑏 𝑄

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The Langmuir isotherms represented as

Where, Ce is the concentration of AsIII (µmol/L), AsIII (µmol/L) and F- (mmol/L) and qe is the biosorption capacity of these ions in µmol/g, µmol/g and mmol/g at equilibrium, respectively (Kundu and Gupta 2006). The isotherm constants ‘Q0’ is monolayer biosorption saturation capacity (µmol/g and mmol/g) and ‘b’ represent the enthalpy of biosorption (L/µmol or L/mmol) 12

and were calculated from the slope and intercept of plot between Ce/qe and Ce. An important characteristic of the Langmuir isotherm is expressed in a dimensionless constant separation factor or equilibrium parameter RL (Baig et al. 2010). The RL value indicates the phenomenon of

𝑅𝐿 =

1 → (5) 1 + 𝑏𝐶𝑖

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sorption at constant temperature and is given as

The Q°, b, r2 and RL values of Langmuir isotherms are given in table 2. The value of b for AsIII, AsV and F- was 5.33 L/µmol, 8.09 L/µmol and 97.9 L/mmol, respectively, indicated that biosorbent has greater attraction for all three ions. The r2 values of AsIII, AsV and F- were 0.999,

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0.990 and 0.999 respectively, which indicate the applicability of Langmuir isotherm, because r2

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values was > 0.900.

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RL values between 0 and 1 indicate a favorable sorption process, the shows irreversible sorption, while 1 value designates that a linear sorption is carried out, while RL>1 signifies

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unfavorable sorption process (Mckay et al. 1982). The biosorption of AsIII, AsV and F- on the

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peel of C. pubescens is a favorable process (RL = 0 to 1).

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3.6.2 Freundlich sorption isotherm The Freundlich isotherm describes the sorption equilibrium on heterogeneous surfaces

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and linear form of the isotherm which can be given in detail in the literature (Baig et al., 2010; Meenakshi and Viswanathan 2007; Kundu and Gupta 2006). Freundlich isotherm results showed

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that the r2 value for AsIII, AsV, and F- were 0.895, 0.728 and 0.637, respectively (Table 2), which showed a lower value of r2 value than 0.900, indicated that Freundlich model was not fit well with the experimental data.

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3.6.3 Dubinin–Radushkevich (D–R) sorption isotherm The equilibrium data were also applied to Dubinin–Radushkevich (D–R) isotherm (Namasivayam and Sureshkumar 2008) to evaluate the nature of sorption processes as physical

the following linear form:

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or chemical. This model predicts the heterogeneity of the surface energies and can be written in

𝑙𝑛 𝑞𝑒 = 𝑙𝑛 𝑋𝑚 − 𝛽𝐹 2 → (7) F is calculated as 1 ) → (8) 𝐶𝑒

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𝐹 = 𝑅𝑇 𝑙𝑛 (1 +

where qe is the experimental biosorption capacity (mol/g), D-R isotherm constants, Xm is the

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calculated maximum biosorption capacity (mol/g), β is the activity coefficient (mol2/J2) related to

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biosorption mean free energy (kJ/mol) and F is the Polanyi sorption potential, where R (8.314 J/mol. K) is the gas constant, Ce is the concentrations at equilibrium (mol/L) and T is the

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the plot of lnqe against F2.

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absolute temperature in Kelvin. The constant β and Xm were obtained from slope and intercept of

The mean sorption energy (E), defined as free energy transfer of 1mol of solute from

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solution to the surface of biosorbent material, can be calculated as: 𝐸=

1 √−2𝛽

→ (9)

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The value of r2 in this model for AsIII, AsV and F- were observed to be 0.871, 0.761 and

0.675, respectively. Table 2 indicates the value of the apparent energy of biosorption for these ions on fruit’s peel of C. pubescens were obtained as 15.8, 15.8 and 22.4 kJ/mol, respectively, which indicates that the value of E is > 8 kJ/mol, means the sorption process is supposed to proceed via chemisorptions between sorbates and biosorbent (Mohan and Pittman 2006). 14

3.7 Thermodynamic Study The temperature was a major factor influencing the distribution of sorbate [AsIII, AsV and F-] between biosorbent and liquid phases. The effect of temperature in the range of 303–323K

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was monitored to evaluate the sorption under the optimized conditions. The change in thermodynamic parameters as Gibb’s free energy of sorption (∆G◦), the heat of sorption or enthalpy (∆H◦) and entropy (∆S◦) were evaluated from the following equations: ∆𝐺 ° = −𝑅𝑇𝑙𝑛𝐾𝑜 → (10)

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and

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∆𝐻 ° ∆𝑆 ° + → (11) 𝑅𝑇 𝑅

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𝑙𝑛𝐾𝑜 = −

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where R is a gas constant (0.008314 kJ/mol/K), T is the temperature (K) and Ko is the

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thermodynamic equilibrium constant, which is at equilibrium conditions equal to the

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concentration of sorbate on solid/concentration of sorbate in liquid. The values of ∆H° and ∆S° calculated from the slope and intercept of a plot of lnKc vs. 1/T (van’t Hoff plot). Table 3 shows

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the negative values of ∆H° and ∆G° describes the exothermic and spontaneous nature of the sorption respectively. The value of change in entropy is also negative, that proposes no

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significant change occurred in the internal structure of fruit’s peel of C.pubescens during the

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biosorption processes (Gupta et al. 2005), and the sorbate ions are stable on the solid surface resulting loss of degrees of freedom at solid/liquid interface (Raji and Anirudhan 1998). It was observed that the uptake of AsIII, AsV and F- decreases with increase in temperature and the process for all ions biosorption on fruit’s peel of biosorbent were spontaneous.

15

3.8 Interference Study Surface and ground water contains many different anions and cations, which may have negative or positive effects on the biosorption of AsIII, AsV and F-. The sorption of As species

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and F- ions in the presence of other cations and anions may be affected due to precipitation, complex formation or competition for sorption sites. In this study the influence of Na+, K+, Ca2+, Mg2+, Se4+ and Fe3+ ions on the biosorption of AsIII, AsV, by varying the concentrations from 100 to 1000 mg/L, while the effect of Cl-, Br-, NO3- and SO42- were investigated at 200 mg/L concentration on the F- sorption. The removal of both AsIII and AsV was negatively affected by

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the presence of Ca2+, Mg2+and Se4+, this may be due to more or less same ionic radii to AsIII and

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AsV, while the small negative effect of Na+ and K+ but the difference was not significant (Fig.

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7a). The presence of Fe3+ ion enhanced the biosorption capacity of AsIII and AsV, may due to

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shifting the surface of the biosorbent to more positively charged nature, which in turn enabled the biosorbent to show higher affinity for AsIII and AsV ions. This means the beneficial effect for

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the treatment As contaminated groundwater that usually contains a large amount of dissolved

TE

Fe3+ ion. The Br- and Cl- ions have a small negative effect on the F- sorption may be due to the

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influence of competing anions (Fig. 7b). Among all anions SO42- has a large negative effect on Fbiosorption might be due to higher negative charge compared to that of Cl-/ Br-.

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3.9 Desorption study

A

Desorption of adsorbed As species and F- ions onto biosorbent material was carried out

by using NaOH, HCl and HNO3 at different concentration (Table 4). It was observed that 1M HCL desorbed > 90% of all AsIII, AsV and F- simultaneously while other solution desorbed < 90% of these ions from studied biosorbent (Table 4). The biosorbent used efficiently after regeneration with 1M HCl by five times and then it’s desorption percentage decreases < 90%. 16

3.10 Field Study This study has demonstrated the applicability of the fruit’s peel of C. pubescens an indigenous biosorbent material for the simultaneous removal of As species and F- from

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groundwater of different sites (D-1 to D-5) of Diplo subdistrict. The original samples have AsIII, AsV and F- concentrations in the range of 40 - 79.0 µg/L, 103 - 398 µg/L and 4.27 - 16.7 mg/L respectively. These original samples (20 ml) were treated with biosorbent material at optimized conditions (Dosage 5g/L, shaking time 50min and temperature 303K), after biosorption AsIII, AsV and F- and were obtained in the range of 4.43 - 20.5 µg/L, 8.55 - 19.8 µg/L and 0.55 - 1.86

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mg/L (Table 5). The water samples of studied area are highly contaminated with As species and

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F- due to leaching from soil (Brahman et al. 2014). The relative standard deviation was < 5%

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indicates the efficiency of biosorbent material for the removal of As species and F- ions. 4. Conclusion

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The biomass fruit’s peel of C. pubescens demonstrated a good capacity of As species and

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F- biosorption simultaneously. The biosorption was rapid and equilibrium achieved within 50 min. The AsIII, AsV and F- have maximum biosorption capacities of selected biomass were found

EP

as 25.6, 75.5 and 2.955 mg/g, respectively, from water samples at optimized conditions of pH

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7.0, dosage 5g/L, contact time of 50 min and temperature of 303K. Sorption isotherm constants were evaluated by Langmuir, Freundlich and D–R isotherms and the results indicate that

A

Langmuir model was in good agreement with the experimental results. The mean free energy values calculated from the D–R model was found to be >8.0kJ/mol, indicated that the biosorption of As species and F- ions using fruit’s peel of C. pubescens might be chemisorption. Kinetic evaluation of the equilibrium data showed that the biosorption of As species and F- onto biosorbent material followed well the pseudo-second-order kinetic model. No significant 17

influence on the removal of As species and F- by the biosorbent were observed in the presence of Na+, K+, Ca2+, Mg2+, Fe3+,Se4+, Cl-, SO42-, Br-, and NO3-, it means a selective method for removal of them. Biosorbent is cheap and available in large quantity, whereas it can be regenerated by 1.0

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M HCl solution. Acknowledgments

The authors are grateful for the financial support of the Higher Education commission (HEC),

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Islamabad (Pin # 112-26591-2Ps1-182).

18

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Asadullah M, Jahan I, Ahmed MB, Adawiyah P, Malek NH, Rahman MS. 2014. Preparation of

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Wang JW, Bejan D, Bunce NJ. 2003. Removal of arsenic from synthetic acid mine drainage by electrochemical pH adjustment and coprecipitation with iron hydroxide. Environ Sci Technol 37:4500-4506.

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Yang MM, Hashimoto T, Hoshi N, Myoga H. 1999. Fluoride 466 removal in a fixedbed packed with granular calcite. Water Res 33:3395-3402. Zhu C, Bai G, Liu X, Li Y. 2006. Screening high-fluoride and high-arsenic drinking waters and

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Res 40:3015-3022.

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Figure Caption Fig.1. Particle size distribution of the peel of C. pubescens Fig.2. FTIR analysis showed the difference between the spectra of unloaded biosorbent ( 2a),

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biosorbent loaded with F- (2b) and biosorbent loaded with As ions (2c). Fig.3. Scanning electron micrographs of (3a) peel of C. pubescens and (3b) peel of C. pubescens loaded with As species, (3c) peel of C. pubescens loaded F- and (3d) peel of C. pubescens loaded with As species and F- simultaneously.

Fig.4. The effect of pH on the removal of As(III) As(V) and F- at the parameters of 5 g/L biosorbent dose, 2 h contact time and 303 K temperature.

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Fig.5. Effects of (a) As(III) and As(V) concentrations and (b) F- concentration on biosorption to

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the peel of Cucumis pubescens at biosorbent dose 5 g/L, contact time 2 h and pH 7.0.

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Fig.6. Effect of dosage on the biosorption of As(III) As(V) and F- to biomass peel of Cucumis

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pubescen.

Fig.7. The influence of (a) Na+, K+, Ca2+, Mg2+, Se4+ and Fe2+ ions on the biosorption of As(III)

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and As(V) and (b) Cl-, Br-, NO3- and SO42- on the F- biosorption.

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26

D

TE

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CC

A

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D

TE

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CC

A

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A

M

28

D

TE

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CC

A

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29

D

TE

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A

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A

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30

D

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Table 1. Kinetic parameters obtained from pseudo-first-order and pseudo-second-order for As(III), As(V) and F- sorption onto peel of C. pubescens fruit Pseudo 1st order

Pseudo 2nd order

Adsorbate Cal. qe

r2

k2

Cal. qe

r2

As(III)

0.0990

1.22*

0.304

0.0972***

0.476*

0.994

As(V)

0.136

7.02*

0.422

0.0296***

1.45*

0.978

F-

0.0622

0.469**

0.124

0.129****

0.250**

0.948

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k1(1/min)

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*µM/g, ** mM/g, ***g /µMmin, *****g/mMmin

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Table 2. The parameters of As(III), As(V) and F- onto Peel of C. pubescens fruit in Langmuir, Freundlich and D–R sorption isotherm. As(V)

F-

Q˚ (µmol/g or mmol/g)

0.357

1.09

0.160

b (L/µmol or L/mmol)

5.33

r2

0.999

RL

0.000625

Langmuir isotherm

Cm (µmol/g or mmol/g)

0.999

0.000309

0.000638

6.02

0.895

0.728

0.637

1.97E-06

1.48E-05

0.000295

-2E-09

-2E-09

-1E-09

r2

0.871

0.761

0.675

E (kJ/mol)

15.8

15.8

22.4

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2.52

n

5.40

D

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Xm (mol/g)

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β (mol2/J2)

A

CC

0.990

0.194

r2

Dubinin– Radushkevich (D–R) isotherm

97.9

1.10

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Freundlich isotherm

0.273

8.09

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Parameter

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As(III)

Model

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Table. 3. Thermodynamic parameters for sorption of As(III), As(V) and F- on Peel of C. pubescens fruit at different temperatures Temperature (K) Element

Parameters

∆G° (kJ/mol) As(III)

-12.6

∆H° (kJ/mol)

-20.4

∆H° (kJ/mol)

-11.5

-19.7

-18.9

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-43.9

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∆S° (kJ/mol.K)

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∆G° (kJ/mol)

-19.6

-0.0774 -18.6

-18.1

-42.2 -0.0749

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D

M

∆H° (kJ/mol) ∆S° (kJ/mol.K)

-11.6

-0.0572

∆G° (kJ/mol)

F-

323

-29.8

∆S° (kJ/mol.K)

As(V)

313

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303

34

Table 4. Percentage desorption of As(III), As(V) and F- from studied biosorbent by different solutions. As(III) (%)

As(V) (%)

F- (%)

0.5

79.2

84.5

82.1

1.0

92.1

0.5

68.8

1.0

76.4

0.5

70.5

1.0

78.9

HCl

HNO3

94.6

92.5

70.7

72.3

74.5

78.7

73.2

67.4

80.7

75.6

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NaOH

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Concentration (M)

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Eluent

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Table. 5. The concentrations of As(III), As(V) and F- in the groundwater samples of Diplo, Pakistan before and after sorption on Peel of C. pubescens fruit F- (mg/L)

As(V) (µg/L)

After adsorption

Removal (%)

Before adsorption

After adsorption

D-1

40.0

4.43

88.9

103

8.55

D-2

79.0

6.77

91.4

208

16.4

D-3

159

20.5

87.1

398

19.8

D-4

54.0

10.2

81.0

149

9.12

D-5

79.0

7.05

91.1

210

Removal (%)

After adsorption

Removal (%)

15.6

0.900

94.2

92.1

16.7

1.86

88.9

75.9

16.3

1.49

90.9

93.9

4.27

0.550

87.1

91.9

6.52

0.720

89.0

A

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D

M

A

16.9

Before adsorption

91.7

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Before adsorption

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As(III) (µg/L)

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Sample I.D

36