Biosorptive removal of arsenic from drinking water

Biosorptive removal of arsenic from drinking water

Bioresource Technology 100 (2009) 634–637 Contents lists available at ScienceDirect Bioresource Technology journal homepage:

173KB Sizes 51 Downloads 198 Views

Bioresource Technology 100 (2009) 634–637

Contents lists available at ScienceDirect

Bioresource Technology journal homepage:

Biosorptive removal of arsenic from drinking water Piyush Kant Pandey a,*, Shweta Choubey a, Yashu Verma a, Madhurima Pandey a, K. Chandrashekhar b a b

Centre for Environmental Science and Engineering, Department of Engineering Chemistry, Bhilai Institute of Technology, Durg 491002, CG, India Analytical Chemistry Group, Defence Metallurgical Research Laboratory (DMRL), Hyderabad 500058, AP, India

a r t i c l e

i n f o

Article history: Received 16 May 2007 Received in revised form 8 July 2008 Accepted 12 July 2008 Available online 21 September 2008 Keywords: Arsenic Adsorption Biomass Momordica charantia

a b s t r a c t A biomass derived from the plant Momordica charantia has been found to be very efficient in arsenic(III) adsorption. An attempt was made to use this biomass for arsenic(III) removal under different conditions. The parameters optimized were contact time (5–150 min), pH (2–11), concentration of adsorbent (1– 50 g/l), concentration of adsorbate (0.1–100 mg/l), etc. It was observed that the pH had a strong effect on biosorption capacity. The optimum pH obtained for arsenic adsorption was 9. The influence of com mon ions such as Ca2+, Mg2+, Cd2+, Se4+, Cl, SO2 4 , and HCO3 , at concentrations varying from 5 to 1000 mg/l was investigated. To establish the most appropriate correlation for the equilibrium curves, isotherm studies were performed for As(III) ion using Freundlich and Langmuir adsorption isotherms. The pattern of adsorption fitted well with both models. The biomass of M. charantia was found to be effective for the removal of As(III) with 88% sorption efficiency at a concentration of 0.5 mg/l of As(III) solution, and thus uptake capacity is 0.88 mg As(III)/gm of biomass. It appears that this biomass should be used as a palliative food item. Further it also appears that the dietary habits may play a role in the toxic effects of ingested arsenic. Ó 2008 Elsevier Ltd. All rights reserved.

1. Introduction Arsenic is highly toxic and has historically been used as a poison. Acute poisoning has a mortality rate of 50–75%, and death usually occurs within 48 h. The arsenic contamination has been acknowledged as a ‘‘major public health issue” (WHO, 1999). Arsenic is classified as a group A and category 1 human carcinogen by the US Environmental Protection Agency (US EPA, 1997) and the International Association For Research on Cancer (IARC, 2004), respectively. The WHO provisional guideline of 10 ppb (0.01 mg/l) has been adopted as the drinking water standard. However, many countries have retained the earlier WHO guideline of 50 ppb (0.05 mg/l) as their standard or as an interim target including Bangladesh and China. In 2001, US EPA published a new 10 ppb (0.01 mg/l) standard for arsenic in drinking water, requiring public water supplies to reduce arsenic from 50 ppb (0.05 mg/l). Pandey et al. (1999, 2000, 2001) first reported arsenic contamination and human affliction at places far away from the Bengal Delta Plains in erstwhile Madhya Pradesh. The majority of arsenic in natural water is a mixture of arsenate and arsenite, with arsenate usually predominating. High concentration of arsenic in groundwater has been reported from the Bengal Delta Plains in West Bengal and Bangladesh (Bhattacharya et al., 1997). Arsenic is the twentieth most abundant element in the earth (ATSDR, * Corresponding author. Tel.: +91 94252 45309; fax: +91 788 2210163. E-mail address: [email protected] (P.K. Pandey). 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.07.063

1998). Symptoms of arsenicosis are primarily manifested in the forms of different types of skin disorders such as skin lesions, hyperkeratosis, and melanosis. Many scientists have been trying to remove arsenic from the drinking water as well as industrial effluents using adsorptive removal technique (Chakravarty et al., 2002; Dambies, 2004; Kamala et al., 2005; Zeng, 2003). Existing methods of arsenic removal include oxidation (Chiu and Hering, 2000), ion-exchange, precipitation (Chow, 1997), adsorption (Elizalde, 2001; Dambies, 2004; Gregor, 2001), and ultra filtration. The process of adsorption is a good alternative because it can remove the disadvantages of the classical chemical destabilization. Numerous biological materials have been tested for the removal of toxic metal ion from aqueous solution over the last two decades. However, only a limited number of studies have been investigated on the use of adsorbents derived from biological sources, e.g. chitosan (Mcafee et al., 2001; Dambies et al., 2002), orange waste (Ghimire et al., 2002, 2003), fungal biomass (Say et al., 2003a,b; Loukidou et al., 2003), activated carbon (AC) produced from oat hulls (Chuang et al., 2005), coconut husk carbon (CHC) (Manju et al., 1998), a low-cost ferruginous manganese ore (FMO) (Suzuki et al., 2000), Garcinia cambogia (Kamala et al., 2005), alkaganeite (Solozhenkin et al., 2003), oxisol (Ladeira and Ciminelli, 2004), shirasu-zeolite (Xu et al., 2002), synthetic hydrotalcite (Kiso et al., 2005), lignite, peat chars (Allen et al., 1997; Mohan and Chander, 2006), bonechar (Sneddon et al., 2005), to remove arsenic from aqueous solution.

P.K. Pandey et al. / Bioresource Technology 100 (2009) 634–637

This communication reports the removal of As(III) from contaminated drinking water using a novel plant biomass of Momordica charantia. Batch experiments were performed to evaluate the adsorption characteristics of the biomass for As(III) in a synthetic solution.


2. Methods

eluting agents for 30 min at room temperature in a beaker. The biomass was separated from the solution by filtration and washed with deionized water until the pH of the filtrate reached 7. Then the recovered biomass was dried in an electric oven at 60 °C and the capacity to biosorb metal was determined. Batch experiment was conducted to desorb bound As(III) from the biomass using different eluting agents such as NaOH, NaCl, Na2CO3, HCl, and HNO3 at predetermined concentrations.

2.1. Plant collection and preparation of the biomass

2.4. Batch interference studies

The M. charantia plants were collected from the different sites located in the region of Durg, Chattisgarh, India. After the collection, an appropriate body part was plucked and washed with deionized water, then cut into small pieces and subsequently dried in an electric oven at 60 °C for 3 days. The dried biomass was ground and sieved through 100-mesh Tyler screen and the fine biomass obtained was used in the adsorption experiments.

The metal binding capacity experiments were repeated with solution containing the binary mixture of different common ions usually present in water with As(III) solution. The effect of calcium, magnesium, cadmium, selenium, chloride, sulphate, and bicarbonate concentrations varying from 5 to 1000 mg/l was investigated.

2.2. Adsorption study biosorption experiment

The FT-IR study of fresh biomass and metal loaded biomass of M. charantia using the detector DTGS KBr, Beam splitter KBr, infrared source was done with Branch Thermo Nicolet Nexus 670 Spectrometer. This FT-IR study was done in Indian Institute of Chemical Technology, Hyderabad.

Experiments to determine the contact time required for equilibrium sorption experiments were performed in Erlenmeyer flasks, using 1 l of metal solution and approximately 5 g of biomass (dry matter). The flasks were maintained at 28 °C. Samples were removed at different time intervals, filtered and analyzed by hydride generation atomic absorption spectrophotometer (Chemito-302). Batch equilibrium sorption experiments were carried out in 125 ml Erlenmeyer flasks with 50 ml of metal solution and 0.25 g of biomass for 45 min. These experiments were done at pH 2, 3, 4, 6, 8, 9, 10, and 11 at 28 °C. Solutions of 0.1 M NH3 and H2SO4 were used to adjust the pH. After the sorption equilibrium was reached (45 min), the solution was separated from the biomass by filtration. The initial and equilibrium arsenic concentrations in each flask were determined by AAS. The amount of metal ion adsorbed by the biomass was calculated by

qe ¼ C i  C e =m; where Ci is the initial concentration of metal ion (mg/l), Ce is the equilibrium concentration of metal ion (mg/l), m is the mass of adsorbent (g/l) and qe is the amount of metal ion adsorbed per gram of adsorbent. Experiments were carried out in triplicate to ascertain the reproducibility and the results with mean, standard deviation (SD) and standard error (SE) are reported here. Experiments done with blank indicate that no precipitation of metal ions occurred under the conditions selected. Experiment done with control biomass indicates no release of metal by the biomass. The effects of process variables such as pH (2–11), biosorbent dosage (1–50 g/l), initial metal ion concentration (0.1–100 mg/l), contact time, and background ions which are commonly present in drinking water and some ions which are toxic 2  2+ 4+ (5– to living organisms such as Ca2+, Mg2+, HCO 3 , Cl , SO4 , Cd , Se 1000 mg/l), on As(III) uptake were investigated. Quality control checks were carried out by interlaboratory test using ICP-OES (Varian, Australia) at DMRL, Hyderabad.

2.5. FT-IR method

3. Results and discussion 3.1. Effect of pH on biosorption The pH of the aqueous solution is an important controlling parameter in the adsorption process. The effect of pH (2–10) on the removal of As(III) for a constant biosorbent dosage of 5 g/l, standing time 45 min and metal ion concentration of 0.5 mg/l was studied. It was found that pH had a marked effect on the metal uptake in this experiment. The percentage adsorption of metal ion was found to increase with an increase in pH upto 9.5 and then it decreased with a further increase of pH. The optimum pH for the removal of As(III) was found to be 9. It could be related to the fact that with the increase of alkalinity (pH) the value of redox potential (Eh) of arsenic (As3+, As5+, As0, and As3) steadily decreases. Aqueous solution of arsenic acid (H3As5+O4) is formed in a strongly acidic environment at high Eh. The most common species in natural water is HAsO2 4 which is stable under neutral to mildly alkaline water at a negative Eh value. The common aqueous solution of As3+ is arseneous acid (H3AsO3), which is stable in the range of alkalinity, pH 8–10. 3.2. Time dependence studies for metal binding The variation in percentage removal of As(III) with time was studied using the solution of As(III) with initial concentration of 0.5 mg/l, adsorbent dosage 5 g/l at pH 9. The time was varied from 5 to 60 min. On increasing the contact time, the percentage removal (SD 1.41 and SE 1) was found to gradually increase till 45 min. Further increase in time decreased the removal of As(III). Hence, the optimum contact time for As(III) removal was 45 min at pH 9.

2.3. Desorption of the adsorbed metal ions

3.3. Effect of adsorbent dosage on metal adsorption

In order to remove the bound metal ions from the biomass, a known amount of biomass was taken into a 250 ml beaker. Batch kinetic studies were first conducted using the biomass to determine the time needed for the As(III) binding process to reach the equilibrium state. After the biosorption tests, the biomass was washed with deionised water for 15 min and left in 15 ml different

To achieve the maximum adsorption capacity of As(III), the experiment was conducted under optimum conditions (fixed contact time of 45 min, initial concentration of metal 0.5 mg/l at pH 9). The effect of biosorbent dosage (1–50 g/l) on the percentage removal of As(III) was studied. The adsorption was found to increase from 66% to 88% with increasing adsorbent dosage from 1 to 5 g/l.

P.K. Pandey et al. / Bioresource Technology 100 (2009) 634–637

3.4. Effect of initial metal ion concentration The effect of adsorbate concentration was studied by varying As(III) concentration from 0.1 to 100 mg/l, while keeping the adsorbent dosage fixed at 5 g/l, contact time 45 min and the pH 9. The results indicate that the percentage removal gradually decreased with increasing initial concentration of As(III). This is due to lack of available active sites on the adsorbent surface. The percentage removal was 99–20% from 0.1 to 100 mg/l of As(III) solution. 3.5. Adsorption isotherm The quantity of adsorbate that can be taken up by an adsorbent is a function of both the characteristics and concentration of adsorbate and the temperature. Generally, the amount of material adsorbed is determined as a function of the concentration at a constant temperature, and the resulting function is called an adsorption isotherm. The Freundlich and Langmuir isotherms are used most commonly to describe the adsorption characteristics. The Freundlich isotherm is widely used to describe adsorption on a surface having heterogeneous energy distribution. The Langmuir isotherm is applicable to monolayer chemisorption. The equilibrium data for the removal of As(III) by adsorption at pH 9 were used with Freundlich and Langmuir isotherms. The linear form of Freundlich isotherm is

log S ¼ log K F þ ð1=NÞ log C s ; where S is the moles sorbed at equilibrium per mass of sorbent (mg/ g), i.e. (Ce/m), KF is the Freundlich isotherm constant (l/g), N is the Freundlich isotherm constant; N P 1, and Cs is the sorbate concentration in solution at equilibrium (mg/l). The constant KF is the measure of adsorption capacity and 1/N is the measure of adsorption intensity. The linear form of Langmuir isotherm is

S ¼ ðK L AM CÞ=ð1 þ K L CÞ; where S is the moles sorbed at equilibrium /mass of sorbent (mg/g), i.e. Ce/m, AM is the maximum sorption capacity of the sorbent (mg/ g), KL is the Langmuir sorption constant, related to binding energy of the sorbate (l/mg), Cs is the sorbate concentration in solution at equilibrium (mg/l), AM is the maximum sorption capacity of the sorbent, and K is the Langmuir adsorption constant. For Freundlich isotherm plot of log Ce/m against log Cs provides a straight line with a slope of 1/N and an intercept of log KF. And for Langmuir isotherm using the equation, sorption data Cs/Ce/m vs. Cs are plotted to produce a line with a slope of 1/AM and an intercept of 1/(KL AM) Freundlich constant and Langmuir constant were calculated. Results shows that the R2 value is 0.9275 for Freundlich isotherm, which was slightly greater than the R2 value of Langmuir isotherm, i.e. 0.9027, so the results indicate that both models, Langmuir and Freundlich, fit reasonably well with the experimental data. 3.6. Elution tests One of the objective of this work is not only the removal of As(III) from water, but also the recovery of metal as well as reusability of biomass. Reusing of biomass required that the bound species be eluted from the biomass. Elution tests were conducted using the batch technique to select an eluting agent that could desorb all the bound As(III) from biomass. Different eluting agents such as 0.1 M of HCl, HNO3, NaOH, Na2CO3, and NaCl were used. It is evident that the acids HNO3 and HCl performed poorly over

the range of concentrations tested. On the other hand 97% elution of the bound As(III) could be achieved using NaOH. Na2CO3 and NaCl show 85% and 72% recovery, respectively. By using NaOH, Na2CO3, and NaCl as the eluting agents the removal of arsenic from the loaded biomass was maximum, which could be due to the formation of sodium arsenate. 3.7. Studies of influencing co-occurring inorganic solutes The influences of co-ions on arsenic biosorption by the biomass were evaluated. Effect of initial metal ion concentration on the adsorption process of various co-ions Ca2+, Mg2+, Cd2+, Se4+, 2  are shown in Figs. 1 and 2. Results clearly HCO 3 , SO4 , and Cl shows that the percentage removal of As(III) were less than 70% with the presence of a very low concentration of various ions such   2+ 2+ as SO2 4 , Cl , HCO3 , Ca , and Mg . However, in the presence of selenium and cadmium, the removal efficiency was found to increase from 85% to 100%. The decrease of percentage removal in the presence of calcium and magnesium ions may be explained based on the ionic radii. All these ions are bigger than As(III) and that is why in their presence the percentage removal decreases. On the other hand the ionic radii of Cd2+ and Se4+ are nearly the same, so there was no decreasing effect. 3.8. FT-IR studies The interpretation of infrared spectra involves the correlation of absorption bands in the spectrum of an unknown compound with the known absorption frequencies for the types of bonds. The identification of the source of an absorption band are intensity (weak, medium or strong), shape (broad or sharp), and position (cm1) in the spectrum. FT-IR study of fresh biomass and metal loaded

Percentage Removal

Further increase in dosage showed a decrease in the percentage removal of As(III). Hence, the optimum biosorbent dosage is reported as 5 g/l.

120 100 80 60 40 20





0 5







Concentration of co-ionsmg/L Fig. 1. Effects of calcium, magnesium, cadmium, and selenium ions on the biosorption of As(III).


Percentage Removal


60 50 40 30 20 10




0 5







Concentration of co-ionsmg/L Fig. 2. Effects of chloride, sulphate, and bicarbonate ions on the biosorption of As(III).

P.K. Pandey et al. / Bioresource Technology 100 (2009) 634–637

biomass show a major difference in the region 3400–2800 and 1700–1200 cm1 indicating chelation of As(III) with the –OH groups for fresh biomass of M. charantia. The peak around 2940–2920 cm1 is assigned to –OH group of the organic constituents in different parts of the biomass. The FT-IR results of this study showed the shift from 1640 to 1680 cm1. This shift corresponds to the [email protected] group present in the organic acid (Padmarathy et al., 2003). An absorption in the region between 1350 and 1470 cm1 indicates the presence of C–H bonding in alkane, C–O stretching is confirmed by the peak observed in the region between 1080 and 1300 cm1, this indicates that the biomass contains acidic groups. The Biomass also contains amine groups, which is confirmed by the absorption in the region of 1020–1340 cm1 (Ashkenazy et al., 1997). Hence, based on FT-IR spectrum analysis it can be inferred that the metal binding in the biomass of M. charantia takes place by the substitution of amine and carboxylic groups by the As(III). 3.9. Application of biomass for the removal of arsenic from drinking water and as dietary supplement The studies conducted using synthetic metal ion solution (multi-component) revealed the effectiveness of the biomass as a potential sorbent for the removal of As(III) from contaminated ground water. The metal ions and the range of concentrations chosen are representative of contaminated drinking water. In a set of experiments the biomass demonstrated that 0.5 mg/l of arsenic present in the contaminated drinking water could be removed to 85% at pH 9 (adjusted). Reuse of the biomass could be possible by desorbing the metals by the method mentioned in the regeneration experiment. We have also conducted a limited research on the efficacy of this biomass as a dietary supplement to the arsenicosis patients in the Rajnandgaon district of Chhattisgarh state and very encouraging results are being obtained towards the amelioration of the problem. Palliative properties of the biomass have been observed beyond any doubt. 4. Conclusion The biomass of the edible plant of M. charantia demonstrated a good capacity of arsenic biosorption, highlighting its potential for the drinking water treatment process. The biomass was successfully used as biosorbent of As(III) from aqueous solution with 88% sorption efficiency from 0.5 mg/l As(III) solution. pH had a strong effect on biosorption capacity and the optimum pH deduced is 9. The biosorption was rapid and equilibrium achieved within 45 min. The uptake capacity of metal was found to be 0.88 mg/g for 0.5 mg/l of As(III). Adsorption isotherm constant was calculated and the results indicate that both models, Langmuir and Freundlich sorption models, were in good agreement with the experimental results. The influences of various common ions present in drinking water were investigated. No significant influence on removal of As(III) by the biomass was observed in   2+ 2+ the presence of SO2 4 , Cl , HCO3 , Ca , and Mg . And in the presence of selenium and cadmium the removal efficiency was found to be 85–100%. References Allen, S.J., Whitten, L.J., Murray, M., Duggan, O., 1997. The adsorption of pollutants by peat, lignite and activated chars. J. Chem. Technol. Biotechnol. 68, 442–452. Ashkenazy, R., Gottlieb, L., Yannai, S., 1997. Characterization of acetone washed yeast biomass functional groups, involved in lead biosorption. Biotechnol. Bioeng. 55 (1), 1–10. ATSDR (Agency for Toxic Substances and Disease Registry), 1998. Draft Toxicological Profile for Arsenic. Prepared for the US Department of Health and Human Services, ATSDR, by the Research Triangle Institute. August 1998.


Bhattacharya, P., Chatterjee, D., Jacks, G., 1997. Occurrence of as-contaminated groundwater in alluvial aquifers from Delta Plains, Eastern India: options for safe drinking water. Water Res. Dev. 13, 79–92. Chakravarty, S., Dureja, V., Bhattacharyya, G., Maity, S., Bhattacharjee, S., 2002. Removal of arsenic from groundwater using low cost ferruginous manganese ore. Water Res. 36 (3), 625–632. Chiu, V.Q., Hering, J.G., 2000. Arsenic adsorption and oxidation at manganite surfaces. 1. Method for simultaneous determination of adsorbed and dissolved arsenic species. Environ. Sci. Technol. 34 (10), 2029–2034. Chow, W., 1997. Removing traces elements from power plant wastewater. Pollut. Eng. 19, 54–55. Chuang, C.L., Fan, M., Xu, M., Brown, R.C., Sung, S., Saha, B., Huang, C.P., 2005. Adsorption of arsenic(V) by activated carbon prepared from oat hulls. Chemosphere 61 (4), 478–483. Dambies, L., 2004. Existing and prospective sorption technologies for the removal of arsenic in water. Separation Sci. Technol. 39, 603–627. Dambies, L., Vincent, T., Guibal, E., 2002. Treatment of arsenic containing solution using chitosan derivatives: uptake mechanism and sorption performances. Water Res. 36, 3699–3710. Elizalde, M.P., 2001. Sorption on natural solids for arsenic removal. Chem. Eng. J. 81, 187–195. Ghimire, K.L., Inoue, K., Yamaguchi, H., Makino, K., Miyajima, T., 2003. Adsorptive separation of arsenate and arsenite anions from aqueous medium by using orange waste. Water Res. 37, 4945–4953. Ghimire, KN., Inoue, K., Makino, K., Miyajima, T., 2002. Adsorptive removal of arsenic using orange juice residue. Separation Sci. Technol. 37, 2785–2799. Gregor, J., 2001. Arsenic removal during conventional aluminium based drinking water treatment. Water Res. 35 (7), 1659–1664. IARC, 2004. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Some Drinking-Water Disinfectants and Contaminants, including Arsenic, vol. 84. IARC Press, Lyon (192 IARC Monographs, vol. 86). Kamala, C.T., Chu, K.H., Chary, N.S., Pandey, P.K., Ramesh, S.L., Sastry, A.R.K., Chandrashekhar, K., 2005. Removal of As(III) from aqueous solution using fresh and immobilized biomass. Water Res. 39, 2815–2826. Kiso, Y., Jung, Y.J., Yamada, T., Nagai, M., Min, K.S., 2005. Removal properties of arsenic compounds with synthetic hydrotalcite compounds. Water Sci. Technol. Water Supply 5 (5), 75–81. Ladeira, A.C.Q., Ciminelli, V.S.T., 2004. Adsorption and desorption of arsenic on an oxisol and its constituents. Water Res. 38 (8), 2087–2094. Loukidou, M.X., Matis, K.A., Zouboulis, A.I., Liakopoulou-Kyriakidou, M., 2003. Removal of As(V) from wastewater by chemically modified fungal biomass. Water Res. 37, 4544–4552. Manju, G.N., Raji, C., Anirudhan, T.S., 1998. Evaluation of coconut husk carbon, for the removal of arsenic from water. Water Res. 32 (10), 3062–3070. Mcafee, B.J., Gould, W.D., Nadeau, J.C., da Costa, A.C.A., 2001. Biosorption of metal ions using chitosan, chitin and biomass of Rhizopus oryzae. Separation Sci. Technol. 36, 3207–3222. Mohan, D., Chander, S., 2006. Removal and recovery of metal ions from acid mine drainage using lignite—a low cost sorbent. J. Hazard. Mater. 137 (3), 1545–1553. Padmarathy, V., Vasudevan, P., Dhingra, S.C., 2003. Thermal end spectroscopic studies on sorption of Ni(II) ion on protonated bakers yeast. Chemosphere 52 (10), 1807–1817. Pandey, P.K., 2000. Who should be credited for the discovery and first reporting of arsenicosis in Kaudikasa in Madhya Pradesh? Curr. Sci. 78, 1412. Pandey, P.K., Khare, R.N., Sharma, S., Pandey, M., 1999. Arsenicosis and deteriorating ground water quality: unfolding crisis in central East Indian region. Curr. Sci. 77, 686–693. Pandey, P.K., Yadav, S., Nair, S., Sar, S., Pandey, M., 2001. Holistic theory of arsenic contamination. In: 3rd International India/Bangladesh Symposia on Reducing the Impact of Toxic Chemicals in the Bengal Basin, Kolkata, India. 10–12 February. Available from: . Say, R., Yilmaz, N., Denizli, A., 2003a. Biosorption of cadmium, lead and arsenic ions by the fungus Penicillium purpurogenum. Separation Sci. Technol. 38, 2039– 2059. Say, R., Yilmaz, N., Denizli, A., 2003b. Removal of heavy metal ions using the fungus Penicillium canescens. Adsorption Sci. Technol. 21, 643–650. Sneddon, R., Garelick, H., Valsami-Jones, E., 2005. An investigation into arsenic(V) removal from aqueous solutions by hydroxylapatite and bonechar. Mineral. Mag. 69 (5), 769–780. Solozhenkin, P.M., Deliyanni, E.A., Bakoyannakis, V.N., Zouboulis, A.I., Matis, K.A., 2003. Removal of As(V) ions from solutions bt akaganeite_FeO(OH) nanocrystals. J. Mining Sci. 39 (3), 287–296. Suzuki, T.M., Bomani, J.O., Matsunaga, H., Yokoyama, T., 2000. Preparation of porous resin loaded with crystalline hydrous zirconium oxide and its application to the removal of arsenic. React. Funct. Polym. 43 (1–2), 165–172. US EPA (US Environmental Protection Agency), 1997. IRIS (Integrated Risk Information System) On-line Database Maintained in Toxicology Data Network (TOXNET) by the National Library of Medicine, Bethesda, Maryland. WHO (World Health Organization), 1999. Arsenic in Drinking Water, Fact Sheet No. 210, Geneva. Xu, Y.-H., Nakajima, T., Ohki, A., 2002. Adsorption and removal of arsenic(V) from drinking water by aluminum-loaded shirasu-zeolite. J. Hazard. Mater. 92 (B), 275–287. Zeng, L., 2003. A method for preparing silica-containing iron(III) oxide adsorbent for arsenic removal. Water Res. 37, 4351–4358.