Article pubs.acs.org/IECR
Evaluation of Iron(III) Chelated Polymer Grafted Lignocellulosics for Arsenic(V) Adsorption in a Batch Reactor System S. Rijith,† T. S. Anirudhan,†,* and T. Shripathi‡ †
Department of Chemistry, University of Kerala, Kariavattom Campus, Thiruvananthapuram 695 581, India UGC-DAE−CSR, University Campus, Khandawa Road, Indore-452017, India
‡
ABSTRACT: A novel adsorbent, iron(III) chelate of an amino-functionalized polyacrylamide-grafted coconut coir pith (Fe(III)A-PGCP) was prepared and used for the removal of arsenic(V) from aqueous solutions. The adsorbent was prepared by graft copolymerization of acrylamide onto coconut coir pith, CP (a lignocellulosic residue) in the presence of N,N′methylenebisacrylamide as a cross-linking agent followed by treatment with ethylenediamine and ferric chloride in acid (HCl) medium. The adsorbent was characterized using Fourier transform infrared (FTIR) spectroscopy, Raman analysis, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM/EDS), surface area analysis, determination of amine and iron moieties on the surface of the adsorbent, and batch adsorption experiments were carried out under a variety of operating conditions such as contact time, initial sorbate concentration, pH, adsorbent dose, presence of interfering ions, and temperature. The results showed a maximum adsorption (>99.9%) at pH 7.0. Kinetic data were modeled using pseudo-first-order, pseudo-second-order, and Ritchie-modified secondorder models. The kinetic data were best described by a pseudo-second-order equation. Adsorption equilibrium data were correlated with Langmuir, Freundlich, and Sips isotherms. The results showed that the Langmuir isotherm model seemed to successfully simulate the adsorption isotherm curve and the maximum adsorption capacity was estimated to be 107.8 mg/g at 30 °C. The reusability of the spent adsorbent for several cycles was demonstrated using 0.1 M HCl. The residual arsenic concentration was brought down from 1.0 mg/L to 0.01 mg/L (more than 99.0%) was achieved with a Fe(III)-A-PGCP dose of 150 mg in a 50-mL sample. A counter-current batch adsorber was designed using operating lines.
1. INTRODUCTION Recently, surface and groundwater contamination by arsenic has been recognized as a global problem, since it is virtually present on every continent.1 Weathering of arsenic minerals (arsenopyrites) in oxidizing environments solubilizes arsenic as As(III) and As(V). Arsenic is widely dispersed in the environment, where maximum mobilization of arsenic in soil and groundwater occurs under natural conditions such as weathering reactions and biological activities in soils.2 It is also introduced mainly through human activities such as mining wastes, nonferrous smelting activities and ceramics, petroleum refining, fossil fuel power plants, sewage sludge, pesticides, fertilizers, and metallurgic industrial processes leading to anthropogenic arsenic contamination.3 The long-term uptake of arsenic contaminated water causes liver, lung, kidney, bladder, skin, and nerve tissue injuries.4 Based on the impact on human health, the WHO’s provisional guideline of 0.01 mg/ L has been adopted as the drinking water standard.5 In 2006, the United States Environmental Protection Agency (USEPA) set the arsenic standard for drinking water at 0.01 mg/L, to protect consumers served by public water systems from the effects of long-term chronic exposure to arsenic. However, many countries like Argentina, China, Nepal, and Bangladesh have retained the earlier World Health Organization (WHO) guidelines of 50 ppb (0.05 mg/L) as their standard.6 Water systems were required to comply with this standard by January 2006. Therefore, the removal of arsenic from wastewater and contaminated drinking water is one of the most essential issues, with regard to environmental protection and conservation. © 2012 American Chemical Society
A variety of methods, including oxidation−reduction, precipitation, adsorption, electrolysis, cementation, coprecipitation, solvent extraction, ion exchange, ion floatation, foam flotation, and bioremediation, have been proposed to negotiate the problem of arsenic contamination in water.6 Among these, adsorption is becoming more and more popular, because of its low cost, simplicity, high efficiency, potential of regeneration, and sludge-free operation.7 Iron or iron-coated materials are commonly employed as adsorbents for arsenic removal from the contaminated water. Fe(III)-bearing sorbents such as ironmodified activated carbon,8 iron hydroxides and oxides,9 opencelled cellulose sponge,10 akaganeite,11 Fe(III)-loaded cellulose,12 cellulose loaded with iron oxyhydroxides and Fe(II−III) hydroxychloride,13 Fe(III)-doped alginate gels,14 and Fe(III)modified zeolite15 have been cited in the literature for the removal of arsenic from wastewater. Lignocellulosic materials are well-known for their ion exchange capacity and are identified as potential candidates for heavy-metal removal from water. The main disadvantages of these materials are their low resistance to abrasive forces in batch or column operation and leaching of soluble organics (water extracts) during adsorption. Chemical treatments such as esterification and quarternization have been reported to improve the physical and chemical properties of lignocellulosic Received: Revised: Accepted: Published: 10682
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Figure 1. Proposed mechanistic pathway for the synthesis of Fe(III)-A-PGCP and the sorption mechanism.
materials and also to increase their adsorption capacity.16 In the present study, we use coconut coirpith (CP), a lignocellulosic residue, as a precursor material to prepare an efficient adsorbent for arsenic(V) removal from water. India, which is the third largest producer of coconut in the world, produces approximately nine million tonnes of coconuts per year in a vast area of two million hectares.17 A large quantity of CP (byproduct of coir fiber extraction) was accumulated at coir production sites for years. The ratio of coir fiber production to CP is 1:2. It is estimated that the production of CP in India is about 7.5 million tons per year.18 In recent years, attention has been focused on the utility of CP as adsorbent material for wastewater treatment. Parab et al.19 stated that CP could be an effective adsorbent for
cobalt(II) removal from aqueous solutions. However, the applicability of unmodified CP has been found to be limited because of the leaching of organic substances such as lignin, tannin, and pectin into the solution. Chemical-mediated structural modifications such as cross-linking or insertion of new functional groups or grafting of vinyl monomers on CP have been investigated to prevent its dissolution in acidic and basic media or to improve adsorption properties. Earlier studies have shown that the products obtained from modified CP exhibit outstanding adsorption capacity for heavy metals.20,21 In this work, we have prepared a novel amine-modified polyacrylamide grafted CP adsorbent (A-PGCP) by means of simple graft copolymerization reaction followed by loading with Fe(III) in the presence of HCl to utilize it for the effective 10683
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and V is the volume of aqueous solution. The adsorbent Fe(III)-loaded A-PGCP is designated as Fe(III)-A-PGCP. The adsorbent was filtered, washed with water, and then dried at 60 °C for 24 h. The adsorbent with an average particle size of 0.096 mm was used for adsorption experiments. 2.3. Apparatus and Method of Characterization. The Fourier transform infrared (FTIR) spectra of the adsorbent materials were obtained using the pressed disk technique on a Shimadzu Model 1801 FTIR system. Raman spectra were collected using the LabRam HR system (Jobin−Yvon). Laser light of wavelength 532 nm was used for excitation. Depending on the sample background fluorescence, the acquisition time ranged from 10 s to 120 s. To increase the signal/noise ratio, spectra were measured after a photobleaching of 5−30 min. Collected Raman spectra were analyzed and optimized using the ORIGIN program (version 7.5). The spectra were averaged and normalized, and the peaks were deconvoluted. The XRD patterns of the adsorbent samples were obtained with a Siemens Model D 5005 X-ray unit, using Ni-filtered Cu Kα radiation. The specific surface area of CP and Fe(III)-A-PGCP was measured by BET N2 adsorption, using a Quantasorb surface analyzer (QS/7). The pH measurements were made using a systronic microprocessor pH meter (Model μ-362). A potentiometric titration method23 was used to determine the pH of point of zero charge (pHpzc). A UV−vis spectrophotometer (Model V-530, Jasco) was used to estimate residual As(V) ions in solutions by complexing it with an acidic ammonium molybdate reagent containing ascorbic acid and potassium antimony tartrate solutions. In an acidic solution, arsenic forms an yellow complex with molybdate, which is slowly reduced by the ascorbic acid and antimony speeds the reaction process to form a blue antimony arseno molybdate complex. Since the complex showed a maximum absorbance at 885 nm, the absorbance of As(V) solution was measured at this wavelength. The detection limit of As(V) by this method is 10 μg/L.24 Sample morphology and composition were observed and measured using scanning electron microscopy (SEM) (Model JSM-6390 scanning electron microscope) equipped with an INCA Energy 200 EDS-Microanalysis system. The Xray photoelectron spectroscopy (XPS) peaks were decomposed into subcomponents using a Gaussian (80%)−Lorentzian (20%) curvefitting program (XPS peak fit, version 4.1) with a nonlinear background. The full width at half maxima (fwhm) were 1.2, 1.2, and 1.0 eV for C 1s, O 1s, and As(V), respectively. For Fe, a Shirley background subtraction and pure Gaussian line shape were used. The fwhm used to fit the ferric species at 1.4 eV. A temperature-controlled water bath shaker (Labline Instruments Pvt., Ltd., Kochi, India) with a temperature tolerance of ±1 °C was used for equilibrium, kinetic and isotherm studies. The residual concentration of iron(III) in solution was determined using a GBC Avanta-A5450 atomic absorption spectrophotometer (AAS). A titration method25 was used to estimate the accessible amine contents of Fe(III)-APGCP for metal ion adsorption. According to this procedure, 100 mg Fe(III)-A-PGCP was equilibrated with HC1 (0.2 N, 10 mL) with stirring for 24 h. The samples were filtered, washed with distilled water to remove unreacted HCI, and the filtrate was titrated against NaOH (0.2 N) to a phenolphthalein endpoint. 2.4. Adsorption Experiments. Batch adsorption experiments were carried out in 100-mL Erlenmeyer flasks, each of which contained 50 mL of As(V) of desired concentrations. It was agitated with 100 mg of sorbent at 200 rpm in a
removal of As(V) from aqueous media. The functional and analytical characteristics of the sorbent, such as pH or point of zero charge, and sorption capacity, were established and the optimum sorption conditions were determined.
2. EXPERIMENTAL SECTION 2.1. Materials. The CP collected from a local coir industry was washed several times with distilled water to remove surfaceadhered particles and water-soluble materials. Analytical-grade N,N′-methylenebisacrylamide (MBA), ethylenediamine (en), and acrylamide (AAM) were used; all of which were Aldrich products. All the other chemicals used in the experiment were purchased in analytical purity and were used without any further purification. A 1000 mg/L stock solution of As(V) was prepared by dissolving dibasic sodium arsenate, Na2HAsO4·7H2O, analytical-grade (Fluka, Switzerland) in deionized water. 2.2. Adsorbent Preparation and Premise of Study. The CP was oven-dried at 80 °C for 24 h, ground, and sieved using standard test sieves (−80/+230 mesh) to obtain particles of an average diameter of 0.096 mm. The CP basically contains αcellulose, hemicellulose, and lignin, which were determined using the standard methods described by Ott.22 The sensitive component for graft copolymerization might be the methyl hydroxyl groups of the cellulose unit present in CP (CPCH2OH). Figure 1 represents the general procedure adopted for the preparation of A-PGCP. Approximately 20 g of CP was immersed in 200 mL of distilled water in 1-L reaction flasks. Approximately 5 g of MBA, as a cross-linking agent, and 2 g of potassium peroxydisulfate (K2S2O8) were added to it and the mixture was stirred for 5 min. Purified N2 was passed through the vessel for 10 min. The polymerization was started by adding 25 g of acrylamide (AAM) as monomer. The mixture was stirred regularly at 70 °C in a water bath until a solid mass was obtained. The polymerized product was extracted with water in a Soxhlet for 6 h in order to remove the homopolymer (poly AAM) formed during the grafting reaction. The obtained polyacrylamide-grafted CP (PGCP) was collected. The grafting yield was determined and found to be 78.8%. The dried mass was refluxed with 100 mL of ethylenediamine (en) continuously for 8 h. The product A-PGCP was separated and washed with toluene and dried. Iron(III) was loaded onto A-PGCP at pH 1), linear (RL = 1), favorable (0 < RL < 1), or irreversible (RL = 0). RL values between 0 and 1 indicate favorable adsorption. The RL values for the adsorption of As(V) onto Fe(III)-A-PGCP are in the range of 0.103−0.217, which clearly reveal that the adsorption follows a favorable path. All the isotherm parameters were calculated, and the values are presented in Table 2. The Freundlich isotherm is an empirical model and can be used to describe the sorption on heterogeneous surfaces, as well as multilayer sorption. The nonlinear Freundlich equation is given below:
qe = KFCe1/ nF
(10)
Here, KF is the Freundlich constant related to adsorption capacity (mg1−(1/n) L1/n g−1) and nF is a constant indicating the intensity of adsorption. This isotherm is derived from the assumption that the adsorption sites are distributed exponentially, with respect to the heat of adsorption. The Langmuir−Freundlich (Sips) isotherm model has the following form: qe =
qm (K sCe)ms s
1 + (K sCe)ms
(11)
where qm is the Sips maximum adsorption capacity (mg/g), KS the Sips equilibrium constant , and mS the Sips model exponent. At low sorbate concentrations, the Sips isotherm reduces to the Freundlich isotherm, and at high sorbate concentrations, it predicts a monolayer sorption capacity analogous to that of the Langmuir isotherm. All data analysis was performed using nonlinear least-squares fitting. A Levenberg−Marquardt algorithm was used to iteratively search for the parameters that best fit the data through the minimization of χ2 values between the predicted values of qe from each isotherm equation and the experimental data. The equation for evaluating the best fit model is to be written as n 2
χ =
∑ i=1
Figure 9. Schematic representation for a two-stage cross-current batch adsorption process.
(qe,exp − qe,cal)2 qe,cal
(12)
is to reduce the As(V) solution volume (V(L)) from an initial concentration C0 to Cn mg/L. Initially, when time t = 0, q = 0, the amount of sorbent added is m1 g, then after “n” stages of operation, the sorbent mass becomes mn. The overall mass balance for n stages was determined to be as follows:
Here, qe,cal is the equilibrium adsorption capacity obtained by calculation from models (mg/g), whereas qe,exp is the equilibrium adsorption capacity of experimental data (mg/g). A comparison between the experimental and calculated values of each isotherm model using nonlinear regression analysis was tried, and the results are shown in Table 2. The calculated isotherm plots using Langmuir, Freundlich, and Sips model parameters from Table 2 are also given in Figure 8, showing that the Langmuir model produces the best-fitting isotherm parameter values with the lowest χ2 values. The values of the Langmuir maximum adsorption capacity (Q0) and the Langmuir constant (b) were found to be 107.8 mg/g and 0.046
V (Cn − 1 − Cn) = m(qt , n − q0)
(13)
C − Cn m = n−1 V qt , n − q0
(14)
A Langmuir isotherm plot at room temperature (30 °C) was employed under equilibrium conditions for the process design. 10691
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out four times using 50 mL of 0.1 M HCl as a desorbing agent. After four cycles, the adsorption capacity of Fe(III)-A-PGCP decreased from 99.2% to 92.6% and the recovery of Fe(III)-APGCP in 0.1 M HCl decreased from 96.0% to 90.3% (see Figure 10). This is an acceptable performance for 0.1 M HCl as
Equation 14 then can be rearranged as C − Cn C − Ce C −C m = n−1 = 0 = 0Q bC e o e V qe qe 1 + bCe
qe =
Q obCe 1 + bCe
⎛V ⎞ ⎛V ⎞ = −⎜ ⎟Ce + ⎜ ⎟C0 ⎝m⎠ ⎝m⎠
(15)
(16)
According to the equation, we could construct the operational lines onto the isotherm curve with a slope defined by using V (the volume of sample, in L) and m (the mass of adsorbent, in grams). Figure 8 also shows the operating lines, which are drawn with a slope of −V/m. The operating lines connect (C0, q0) to (Ce, qe) at equilibrium. The final equilibrium solution concentration is predicted from the point of intersection of the operating lines on the Langmuir isotherm for the adsorption of As(V). The operating line having a slope V/m = −0.5 is drawn through the metal concentrations of 50, 100, and 200 mg/L. The corresponding qe values obtained from the Langmuir equation and from the operational line are 22.8, 42.1, and 70.29 mg/g from initial concentrations of 50, 100, and 200 mg/L, respectively. The operating lines also help in determining the theoretical number of stages for the removal of As(V) from aqueous solution. An operating line having a slope V/m = −0.5 was drawn through the initial As(V) concentration in solution, C0 = 200 mg/L and while loading 0 mg/g of adsorbent, as shown in Figure 8. The solution treated contain ‘L’ litre solution and the arsenate concentration was reduced for each stage from C0 to Cn mg/L. Now, the total amount of arsenic removal can be calculated analytically as follows: m
m
∑ Cn− 1 − Cn = ∑ n=1
n=1
Q 0bCe ⎛ m ⎞ ⎜ ⎟ 1 + bCe ⎝ V ⎠
Figure 10. Four cycles of As(V) adsorption−desorption with 0.1 M HCl as the desorbing agent.
a regenerating solution. The small fraction of adsorbed arsenate species that was not recoverable by regeneration presumably indicates that the metal is bound through strong interaction and, as a result, sorption capacity is reduced in the subsequent adsorption−desorption stages. After each desorption experiment, we reintroduced Fe3+ to restore the adsorption sites to almost the same level as the original values and subsequent adsorption experiments were conducted using reintroduced Fe3+ in Fe(III)-A-PGCP. 3.11. Comparison with Other Adsorbents. The experimental isotherm data obtained for Fe(III)-A-PGCP at pH 7.0 and at 30 °C were compared with a commercial anion exchanger (Amberlite IRA 900; see Figure 8b).The values of Q0 and b were determined by a nonlinear regression analysis and were found to be 68.6 mg/g and 0.042 L/mg, respectively. Although a direct comparison is difficult, because of different optimum conditions established for each of the adsorbents, the adsorption capacity of Fe(III)-A-PGCP in this work (107.8 mg/g) appears to be superior to that of other adsorbents used for this purpose. The Q0 values of the adsorption of As(V) on bead cellulose loaded with iron oxyhydroxide,44 iron(III)loaded chelating resin,39 iron(III)-loaded chelated resin,45 and hybrid(polymer/inorganic) fibrous sorbent (FIBAN-As)46 were reported to be 33.2, 55.4, 60.0, and 81.66 mg/g, respectively. The kinetic performance of the adsorption of As(V) onto Amberlite IRA 900 (Figure 7) follows the more-favorable pseudo-second-order path. Thus, As(V) molecules are adsorbed significantly on Fe(III)-A-PGCP; in fact, this method could be used as an alternative procedure for the removal of As(V) from aqueous solutions. 3.12. Cost Estimation. The availability of the precursor materials and the cost of final adsorbent materials are important factors in considering the economic viability of the adsorption process for the removal of As(V) from water and wastewater. To check the economic viability of the adsorption process, the cost of the Fe(III)-A-PGCP was calculated. The precursor material used in the present study (CP) was obtained free of cost from the local coir industry. After considering the expenses for transport, chemicals, electrical energy, and manpower, the
(17)
Here, n is the adsorption system number (n = 1, 2, 3, ..., m). The arsenate removal, Rn in each stage can be evaluated from the equation as follows: m
∑ Rn = n=1
100mQ 0bCe 100(Cn − 1 − Cn) = C0 VC0(1 + bCe)
(18)
It was found that As(V) was reduced from 200 mg/L to 1 mg/L in three stages. These studies demonstrate that the treatment of As(V) in simulated groundwater is not significantly different from the results predicted on the basis of batch experiments with As(V) only. It can be observed that a minimum adsorbent dosage of 50 mg is sufficient for removing 57.4% of the total As(V) from 50 mL of simulated groundwater containing 1.0 mg/L of As(V) in the presence of other ions. The arsenic content could be decreased from 1.0 mg/L to 0.01 mg/L; in other words, >99.0% removal was achieved with a Fe(III)-A-PGCP dose of 150 mg in a 50-mL sample. 3.10. Desorption and Regeneration Studies. To make the adsorption process more economical, and also to obtain practical information on the recovery of As(V) using Fe(III)-APGCP, it is necessary to regenerate the spent adsorbent using different desorbing agents such as 0.1 M NaOH, 0.1 M Na2SO4, 0.1 M NaCl, 0.1 M NaNO3, 0.1 M HCl, and 0.1 M HNO3 at room temperature. Among these, 0.1 M HCl was proved to be the most suitable desorbing agent. To test the suitability and stability of the adsorbent, it was subjected to successive adsorption and desorption cycles. The procedure was carried 10692
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cost of the final developed adsorbent was determined to be approximately $155/kg. The commercial-grade anion exchanger (Amberlite IRA-900, Sigma−Aldrich) that is available in India costs approximately $222/kg. To calculate the adsorption efficiency of Fe(III)-A-PGCP and Amberlite IRA900 for the removal of As(V) from aqueous solution, batch isotherm experiments were performed at pH 7.0 and 30 °C, using the initial As(V) concentration of 25−450 mg/L. The values of Q0 determined using the Langmuir isotherm equation were found to be 107.8 and 102.32 mg/g for Fe(III)-A-PGCP and Amberlite IRA-900, respectively. These results confirm the viable application of Fe(III)-A-PGCP as a low-cost adsorbent.
(3) Pierce, M. L.; Moore, C. B. Adsorption of arsenite on amorphous iron hydroxide from dilute aqueous solution. Environ. Sci. Technol. 1980, 14, 214−216. (4) Pantuzzo, F. L.; Silva, J. C. J.; Ciminelli, V. S. T. A fast and accurate microwave assisted digestion method for arsenic determination in complex mining residues by flame atomic absorption spectrometry. J. Hazard. Mater. 2009, 168, 1636−1638. (5) Guidelines for Drinking Water Quality, 4th ed.; World Health Organization: Geneva, Switzerland, 2011 (ISBN 9789241548151). (6) Mohan, D.; Pittman, C. U. Arsenic removal from water/ wastewater using adsorbentsA critical review. J. Hazard. Mater. 2007, 142, 1−53. (7) Song, S.; Lopez-Valdivieso, A.; Hernandez-Campos, D. J.; Peng, C.; Monroy-Fernandez, M. G.; Razo-Soto, I. Arsenic removal from high-arsenic water by enhanced coagulation with ferric ions and coarse calcite. Water Res. 2006, 40, 364−372. (8) Chen, W. F.; Parette, R.; Zou, J.; Cannon, F. S.; Brian, A. D. Arsenic removal by iron-modified activated carbon. Water Res. 2007, 41, 1851−1858. (9) Appelo, C. A. J.; Weiden, V. D.; Tournassat, C.; Charlet, L. Surface complexation of ferrous iron and carbonate on ferrihydrite and the mobilization of arsenic. Environ. Sci. Technol. 2002, 36, 3096− 3103. (10) Munoz, J. A.; Gonzalo, A.; Valiente, M. Arsenic adsorption by Fe(III)-loaded open-celled cellulose sponge. Thermodynamic and selectivity aspects. Environ. Sci. Technol. 2002, 36, 3405−3411. (11) Saha, B.; Bains, R.; Greenwood, F. Physicochemical characterization of granular ferric hydroxide (GFH) for arsenic(V) sorption from water. Sep. Sci. Technol. 2005, 40, 2909−2932. (12) Zhao, Y.; Huang, M.; Wu, W.; Jin, W. Synthesis of the cotton cellulose based Fe(III)-loaded adsorbent for arsenic(V) removal from drinking water. Desalination 2009, 249, 1006−1011. (13) Refait, P.; Girault, P.; Jeannin, M.; Rose, J. Influence of arsenate species on the formation of Fe(III) oxyhydroxides and Fe(II−III) hydroxychloride. Colloids Surf., A 2009, 332, 26−35. (14) Banerjee, A.; Nayak, D.; Lahiri, S. Speciation-dependent studies on removal of arsenic by iron-doped calcium alginate beads. Appl. Radiat. Isotopes 2007, 65, 769−775. (15) Bonnin, D. Method of removing arsenic species from an aqueous medium using modified zeolite minerals, U.S. Patent 6,042,731, 2000. (16) Sciban, M.; Klasnja, M.; Skrbic, B. Modified soft wood sawdust as adsorbent of heavy metal ions from water. J. Hazard. Mater. 2006, B136, 266−271. (17) Van Dam, J. E. G. Coir Processing Technologies. Improvement of Drying, Softening, Bleaching and Dyeing Coir Fibre/Yarn and Printing Coir Floor Coverings, Technical Paper No. 6; Food and Agriculture Organization of the United Nations (FAO), Common Fund for Commodities (CFC): Amsterdam, The Netherlands, 2002. (18) Chadha., K. L. Coconut research in IndiaA review. Indian Coconut J. 2003, 36, 13−19. (19) Parab, H.; Joshi, S.; Shenoy, N.; Lali, A.; Sarma, U. S.; Sudersanan, M. Esterified coir pith as an adsorbent for the removal of Co(II) from aqueous solution. Biores. Technol. 2008, 99, 2083−2086. (20) Parab, H.; Sudersanan, M. Engineering a lignocellulosic biosorbent−Coir pith for removal of cesium from aqueous solutions: Equilibrium and kinetic studies. Water Res. 2010, 44, 854−860. (21) Unnithan, M. R.; Vinod, V. P.; Anirudhan, T. S. Synthesis, Characterization, and Application as a Chromium(VI) Adsorbent of Amine-Modified Polyacrylamide-Grafted Coconut Coir Pith. Ind. Eng. Chem. Res. 2004, 43, 2247−2255. (22) Ott, E. Cellulose and Cellulose Derivatives; Interscience Publishers: New York, 1946. (23) Schwarz, J. A.; Driscoll, C. T.; Bhanot, A. K. The zero point charge of silica−alumina oxide suspension. J. Colloid Interface Sci. 1984, 97, 55−61. (24) Lenoble, V.; Deluchat, V.; Serpaud, B.; Bollinger, J. C. Arsenite oxidation and arsenate determination by the molybdenum blue method. Talanta 2003, 61, 267−276.
4. CONCLUSIONS In this study, we have demonstrated the ability of a newly developed adsorbent, Fe(III)-A-PGCP to adsorb As(V) from synthetic solutions as well as groundwater samples using batch adsorption experiments. Graft copolymerization of AAM in the presence of MBA onto CP prevents the leaching of organics in acidic and basic media and also improved the chemical stability of Fe(III)-A-PGCP. The sorption of As(V) is pH-dependent, and the best results are obtained at the pH range of 4.0−7.0. Removal efficiencies of >99.0% have been achieved under optimum conditions. The kinetics of the sorption process is found to follow the pseudo-second-order rate law. The Langmuir isotherm model is used to fit the experimental data obtained at different temperatures. As the temperature increased from 20 °C to 50 °C, the maximum arsenate adsorption capacity of Fe(III)-A-PGCP calculated by the Langmuir model correspondingly increased from 104.3 mg/g to 120.0 mg/g. Quantitative removal of 10.0 mg/L arsenate in 1.0 L of simulated groundwater sample was achieved by using 0.2 g of the adsorbent at pH 7.0 and 30 °C. The acid treatment (0.1 M HCl) and reintroduction of Fe3+ lead to a reactivation of the used adsorbent, in which >97.0% of the original adsorption capacity is achieved. The spent adsorbent can be reused for several cycles consecutively without any noticeable loss of capacity. The results of this study suggest that Fe(III)-APGCP exhibits significant potential as an adsorbent in the removal of As(V) ions from aqueous solutions and simulated groundwater.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: tsani@rediffmail.com. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors are grateful to the Professor and Head, Department of Chemistry, University of Kerala, Trivandrum, for providing the laboratory facilities. Also, S.R. expresses his sincere thanks to the University Grants Commission, New Delhi, for the financial support in the form of a Senior Research Fellowship to carry out this work.
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REFERENCES
(1) Nordstrom, D. K. Public healthWorldwide occurrences of arsenic in ground water. Science 2002, 296, 2143−2145. (2) Smedley, P. L.; Kinniburgh, D. G. A review of the source, behavior and distribution of arsenic in natural waters. Appl. Geochem. 2002, 17, 517−568. 10693
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dx.doi.org/10.1021/ie300732t | Ind. Eng. Chem. Res. 2012, 51, 10682−10694
