Removal of Arsenic from Drinking Water by Using the Zr-Loaded

Article pubs.acs.org/jced

Removal of Arsenic from Drinking Water by Using the Zr-Loaded Resin Changhai Li,†,‡ Wei Xu,‡ Dongmei Jia,*,† and Xuewen Liu† †

Research Center of Chemical Engineering and Technology, Binzhou University, Binzhou 256603, China School of Chemistry and Chemical Engineering, Changchun University of Technology, Changchun 130012, China

‡

ABSTRACT: The hydrous zirconium oxide was loaded successfully onto the polymeric adsorbent (D401) to obtain a new adsorbing material (D401Zr). The adsorptive behavior of arsenic from an aquatic environment by using D401-Zr under different experimental conditions was investigated. The results indicated that D401-Zr had a good adsorption capacity to As(V) at pH < 5.2, whereas As(III) was well adsorbed in the pH range from 6.3 to 9.2. The static experiment data showed that the adsorption isotherm presented a good fitting to the Langmuir model. Adsorption kinetics of arsenic at different concentrations was well described in terms of a pseudo-secondorder equation with regard to correlation coefficients and adsorption capacity. The removal percentage of D401-Zr to As(V) still reached more than 90 % in the presence of the coexisting ions such as SO42− and Cl−, but PO43− and F− had a strong inhibition on As(V), which would cause the removal percentage decreasing obviously.

1. INTRODUCTION Arsenic is a highly toxic environmental contaminant to which millions of people are exposed over the world. The element is ubiquitous in water, and almost all living entities are exposed to it. Chronic uptake of arsenic by humans through contaminated water and food may result in serious health effects, including cancers of the bladder, kidney, and liver and other diseases, including peripheral vascular disease, diabetes mellitus, and hypertension.1−4 Meanwhile, arsenic can also cause the inhibition of seed germination and cause plant height and grain yield to be reduced.5 In addition the arsenic accumulation both in the human body and crops can increase day by day.6,7 Therefore, the arsenic problem has become a primary concern in many countries, such as those in Europe and in the U.S.A., which have lowed the drinking water standard to 1.33 × 10−4 mmol·kg−1.8 Recent studies showed that hazardous levels of arsenic on the human exceeded the relevant estimation, so the removal of arsenic from water sources has become increasingly significant, and research leading to the development of new methods and technologies for arsenic removal is imperative. Various methods have been used for the removal of arsenic from water and wastewater such as chemical oxidation,9 membrane processes,10 adsorption,11−14 biological methods,15 ion exchange,16,17 and electrocoagulation.18 Adsorption has excellent removal efficiency with easy operation and simple design and rarely produces secondary pollution to the environment. Many adsorbents have been investigated for wastewater treatment, including zeolite, activated carbon, polymers,19 and ion-exchange resin. A review of the literature reveals that surface modification was an efficient way to improve the adsorption performances of the adsorbent. With © 2012 American Chemical Society

the functionalization of the adsorbent surface, the new functional groups may provide new adsorption sites for solutes from aqueous solutions. In recent years, a great many studies have focused on arsenic adsorption by iron-modified adsorbent due to its excellent properties20 and gained substantial achievement. As we know, zirconium can generate tetranuclear ions [Zr 4 (OH) 8 (H 2 O) 16 ] 8+ and octanuclear species [Zr8(OH)20(H2O)24]12+ in its hydrated form, which ensures sufficient hydroxyl ions and water molecules to participate in ligand substitution with arsenic species. Hydrous zirconium oxide has high resistance against attacks by acids, alkalis, oxidants, and reductants. D401 (Figure 1) owns a large number of carboxyl groups, which can undergo carboxylation with hydrous zirconium oxide and thus causes the formation of a

Figure 1. Structure of D401. Received: October 22, 2012 Accepted: December 17, 2012 Published: December 31, 2012 427

dx.doi.org/10.1021/je301148t | J. Chem. Eng. Data 2013, 58, 427−435

Journal of Chemical & Engineering Data

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microscopy (SEM, Sirion 200 FEI, Hillsboro, OR; Figure 2). The Brunauer−Emmett−Teller (BET) surface area of the D401 resins before and after their impregnation with zirconium was obtained by an automated gas adsorption system (3H2000PS2, Bei Shide Instrument S&T Co. Ltd., Beijing, China). The physical characteristics of the D401 resins before and after their impregnation with zirconium were listed in Table 2.

new composite material of Zr. Because hydrous zirconium oxide and zirconium have a remarkable selectivity to arsenic21 and D401 resin has rich carbonyl groups, the zirconiummodified D401 resin (D401-Zr) was prepared and used for the adsorbent to remove arsenic from drinking water in this paper.

2. MATERIALS AND METHODS 2.1. Chemicals and Reagents. Sodium arsenite was purchased from Beijing Chemical Reagent Co. (Beijing, China) and used as-received. Other chemicals used were of analytical reagent grade and obtained from Shanghai Chemical Reagent Station (Shanghai, China). A stock solution of zirconium (0.25 mol·kg−1) was prepared by dissolving zirconium oxychloride using 0.01 mol·kg−1 of HCl solution. Stock solutions of As(III) and As(V) (100 mg·kg−1) were prepared by dissolving NaAsO2 and Na2HAsO4 using deionized water. The purity of the materials used for this study is given in Table 1.

Table 2. Main Performance of D401 and D401-Zr performance

chemical name

mass purity

purification method

>0.99 0.365 >0.96 >0.99 >0.99 >0.99 >0.99 >0.99 >0.30 >0.99

none none none none none none none none none none

D401

D401-Zr

5.4046 0.03486 21.3152 faint yellow

7.4447 0.02880 18.7272 orange

2.3. Batch Adsorption Studies. Batch adsorption experiments were conducted to study the adsorption behavior of arsenic on Zr-D401 adsorbent by taking 0.05 kg of arsenic solution in 250 mL stoppered conical flasks. The initial pH of the solutions was adjusted by using hydrochloric acid and sodium hydroxide solutions throughout the experiment when necessary. The glass bottles were put in a temperature controlled orbital shaker with a constant speed of 120 rpm at a certain temperature. The residual concentrations of arsenic were analyzed using atomic fluorescence spectrometry (AFS930, Beijing Jitian Instruments Co., Ltd., Beijing, China). The arsenic removal percentage from the solution was calculated as

Table 1. Sample Description zirconium oxychloride hydrochloric acid sodium arsenite sodium chloride sodium sulfate sodium hydrate sodium phosphate sodium fluoride hydrogen peroxide ethanol

−1

BET surface area/m ·g pore volume/cm3·g−1 average pore diameter/nm color 2

Re =

(C0 − Ce) × 100 % C0

(1)

where Re is the arsenic removal percentage (%) and C0 and Ce (mg·kg−1) are the concentrations of arsenic at initial and equilibrium, respectively. The effect of temperature (293, 303, and 313) K was investigated at pH 3.16 with 0.05 kg of different As(V) concentrations from (1, 2, 4, 6, 8, and 10) mg·kg−1 and 0.05 g of adsorbent particles. Adsorption kinetic studies were conducted at initial concentrations from (0.5, 1, and 2) mg·kg−1 using 0.05 g of resin particles. The adsorption capacity of As(V), Qe (or Qt) at equilibrium (or at time t), of the adsorbent was calculated from the following mass balance relationship:22

A macroporous polystyrene chelating ion exchanger (D401) was purchased from Nankai Resin Co. Ltd. (Tianjin, China). 2.2. Preparation and Characterization of Zr-D401 Resin. D401-Zr was synthesized by a coprecipitation method using zirconium, sodium hydroxide, and D401 resin at 298 K. To synthesize the D401-Zr resins, aqueous solutions of 0.25 mol·kg−1 zirconium and D401 resins were mixed under continuous stirring for 24 h at 298 K. Then the solution was mixed with sodium hydroxide rapidly, and the precipitate was separated by filtration. This was followed by repeated washing with deionized water and ethanol until the solution was neutral. The wet solid was dried at 313 K for 24 h to obtain the D401Zr particles. Morphological analysis of the D401-Zr resin surface was determined using field emission scanning electron

Qt =

W (C 0 − C t ) W (C0 − Ce) or Q e = w w

(2)

Figure 2. Morphology of resin (a) D401 and (b) D401-Zr. 428



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where C0 (mg·kg−1), Ct (mg·kg−1), and Ce (mg·kg−1) are the concentrations of arsenic at initial, at time t, and at equilibrium in solution, respectively. w is the amount of the adsorbing materials used for the test (g), and W is the mass of the solution (kg). To asses the effect of coexisting ions on arsenic removal by the D401-Zr resins, batch adsorption tests were performed by equimolar (2 mmol·kg−1) addition of other anions such as SO42−, Cl−, PO43−, and F− at different pH values.

3. RESULTS AND DISCUSSION 3.1. Characterization of Zr-D401 Resin. The general morphologies of D401 and D401-Zr were investigated by using SEM and results are shown in Figure 2a,b. Figure 2a,b exhibits the evident morphological difference between the surface of D401 and D401-Zr. The hydrous zirconium oxide was distributed onto the surface of D401 (Figure 2b). Table 2 showed that the D401-Zr resins surface area increased slightly. However, the pore size and pore volume of the resins decreased to a certain extent due to blockage of their pores by zirconium after modification. The main structure of which was plotted in Figure 3.

Figure 4. Effect of pH on the adsorption of As(V) and As(III) on adsorbent (contact time, 24 h, agitation speed, 120 rpm). ■, As(V); red circle, As(III).

dominant species existing in this acidic region is H2AsO4− (the pKa value of H2AsO4− is 2.24) which was responsible for the adsorption of As(V) in the aqueous solution. Figure 4 also shows D401-Zr obtained the maximum adsorption capacity to As(III) at pH from 6.3 to 9.2, which could be related to the H3AsO3 pKa value (pKa 9.1).27 The As(V) and As(III) adsorption onto D401-Zr may be explained by the mechanisms of ligand exchange reactions (Figure 5). Arsenic substituted hydroxyl ions or water molecules exist in D401-Zr. The pH of the aqueous solution after arsenic adoption had almost no change or increased in the present experiments, which also further supported these mechanisms. Zr(IV) ion can be extensively polymerized and hydrolyzed at relatively low concentration, and it can transform into tetranuclear ions [Zr4(OH)8(H2O)16]8+ and octanuclear ions [Zr8(OH)20(H2O)24]12+; therefore, there will be a lot of hydroxyl ions or water molecules available for involvement in ligand exchange with arsenic anions. In addition, at higher pH, the decrease in arsenic adsorption onto the D401-Zr may be attributed to the competition between arsenic species and the hydroxyl ions for the adsorption sites. 3.4. Effect of Temperature. The effects of temperature on the As(V) removal were carried out at (293, 303, and 313) K, respectively. As shown in Figure 6, the adsorption capacity of As(V) onto D401-Zr increased with temperature increase. The experimental results suggested that the adsorption of arsenic onto D401-Zr was an endothermal process. It may be due to the fact that increasing the temperature can increase the rate of diffusion of the adsorbate molecules across the external boundary layer and in the internal pores of the adsorbent particles.28 In addition, the adsorption of As(V) on the adsorbent can only be generated by the formation of core complexes, so hydrated arsenic molecular dehydration is essential for forming the effective adsorption. Increasing the temperature will reduce the hydration degree of arsenic molecules. In this work, the study of temperature-dependent adsorption provided significant information for the standard Gibbs free energy, enthalpy, and entropy changes with respect to the adsorption process. 3.5. Adsorption Isotherms. The adsorption isotherm is very important for describing adsorption behavior to a solid− liquid system. A large number of mathematical models have been used for describing the equilibrium relationship between Qe and Ce. In this study, the experimental data of the adsorption isotherms was fitted with the Langmuir, Freundlich, and Temkin models, which are the most common types of models describing this system. The isotherm models were

Figure 3. Structure of the main part of D401-Zr.

3.2. Comparison of the Arsenic Removal Rate between D401 and D401-Zr. The removal efficiency of D401 and D401-Zr toward arsenic is listed in Table 3. From Table 3. Removal Percentage of As(III) and As(V) on Different Resinsa Re/% As(V) −1

C0/ mg·kg D401 D401-Zr a

0.5 35.1 98.7

1.0 32.4 99.0

As(III) 2.0 39.8 99.3

0.5 18.1 80.6

1.0 16.5 75.5

2.0 21 69.5

Uncertainty: U(C0) = 0.01 mg·kg−1.

Table 3, it is clear that the removal of arsenic by using D401-Zr in the aqueous solution increased significantly compared with D401. Zr(IV) ion tends to be extensively polymerized and hydrolyzed and converts into octanuclear ions and tetranuclear species,23 and zirconium oxychloride and hydrous zirconium oxide have a remarkable selectivity to arsenic,24,25 which may contribute to the obvious improvement of arsenic removal efficiency. 3.3. Effect of pH on the Adsorption of Arsenic. The effects of initial pH (1.4−12.5) on arsenic adsorption by D401Zr were studied. As shown in Figure 4, the arsenic adsorption capacity depended profoundly on pH.26 When the pH of the aqueous solution was in the weak acidic region, i.e., the pH range from 1.8 to 5.2, the adsorption capacity of As(V) on D401-Zr reached a maximum value. It is probably due to the 429



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Figure 5. Mechanism of arsenic adsorption onto D401-Zr.

concentration of arsenic (mg·kg−1). Linear plot of Ce/Qe versus Ce showed that adsorption followed the Langmuir isotherm (Figure 7a). Values of Qmax and KL were calculated from the slope and intercept of the linear plot. The model parameters calculated from the linear plot and Langmuir constants are listed in Table 4. 3.5.2. Freundlich Model. The Freundlich isotherm which is an empirical equation used to describe heterogeneous systems is generally expressed as follows:30 ln Q e = ln KF + 1/n ln Ce

where Qe refers to the amount of arsenic adsorbed (mg·kg−1) at equilibrium, Ce is the equilibrium concentration of arsenic, KF is the Freundlich constant and gives the capacity of the adsorbent, and 1/n is the heterogeneity factor and can be used as a measure of the deviation from linearity of the adsorption.26 A linear plot of ln Qe versus ln Ce showed that adsorption followed the Freundlich model (Figure 7b). The model parameters calculated from the linear plot and Freundlich constants are also listed in Table 4. If 1/n < 1, then the adsorption process is favorable.31 From Table 4, the 1/n values obtained were all in the range from 0.40 to 0.45, which indicated that the arsenic adsorption onto D401-Zr was favorable. 3.5.3. Temkin Model. The Temkin isotherm can be used to study the heat of adsorption and adsorbate−adsorbent interaction on the adsorbent surface. The linear form of this isotherm is shown in eq 532

Figure 6. Effect of temperature on the As(V) adsorption onto D401Zr (initial As(V) concentration, (1 to 10) mg·kg−1; contact time, 24 h; agitation speed, 120 rpm). ▲, 293 K; ●, 303 K; ■, 313 K.

compared by the correlation coefficient (R2) to identify which was a better fit for the experimental data, which was also critical for optimizing the design of the adsorption process. 3.5.1. Langmuir Model. The Langmuir adsorption isotherm assumes that the adsorbed layer is one molecule in thickness and those equal sites result in equal energies and enthalpies of adsorption. Langmuir model is represented by the following equation:29 Qe =

Q maxKLCe 1 + KLCe

(4)

(3) −1

Q e = B1 ln KT + B1 ln Ce

where Qe is the amount adsorbed at equilibrium (mg·g ) and Qmax and b are the Langmuir constants related to the adsorption capacity (mg·g−1) and the free energy of the adsorption (kg·mg−1), respectively. Ce is the equilibrium

(5)

where B1 is the Temkin adsorption constant and KT is the equilibrium binding constant (kg·mg−1). The linear plot of ln 430



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Figure 7. Isotherm models of (a) Langmuir, (b) Freundlich, and (c) Temkin models for adsorption of As(V) onto D401-Zr (contact time, 24 h; agitation speed, 120 rpm): blue triangle, 293 K; red circle, 303 K; ■, 313 K; blue line, line fit of 293 K; red line, line fit of 303 K; black line, line fit of 313 K.

Table 4. Isotherm Parameters for Arsenic Adsorption onto D401-Zra model Langmuir

Freundlich

Temkin

a

parameter −1

Qmax/mg·g KL/kg·mg−1 R2 KF/mg·g−1 1/n R2 KT/kg·mg−1 B1/kJ·mol−1 R2

293 K

303 K

313 K

10.42737 4.88984 0.98721 9.20688 0.42649 0.98452 96.92941 4.57398 0.96370

10.58388 5.71466 0.98863 10.04935 0.43838 0.97474 85.19765 4.44497 0.98242

11.28417 8.04109 0.99136 11.84429 0.41177 0.90575 111.6594 4.71545 0.95497

Table 5. Comparison of Maximum Adsorption Capacity with Other Adsorbents to As(V) adsorbent D401-Zr IOCS-2 sorghum biomass polymetallic sea nodule La(III)-impregnated alumina titanium dioxide loaded Amberlite XAD-7 resin activated carbon

Qmax/mg·g−1

ref

11.84 0.0426 3.6 0.74 12.88 4.72

present study 20 37 34 36 33

1.05

35

Uncertainty: U(T) = 0.1 K.

adsorption were calculated from the experiments carried out at different temperatures by the following equations:38−40 Qe versus ln Ce is shown in Figure 7c, and the Temkin parameters are presented in Table 4. The adsorption isotherm results (Table 4) indicate that the Langmuir isotherm fit the data better (R2 > 0.98) than the Freundlich and Temkin models. It might be due to homogeneous distribution of active sites on adsorbent surface. The values of Qmax of the Langmuir model at (293, 303, and 313) K increased with temperature increase. Although it was difficult to compare D401-Zr straightforwardly with other adsorbents due to different experimental conditions, we still found that the maximum adsorption of As(V) on D401-Zr was relatively higher than that for most other adsorbents listed in Table 5.20,33−37 Consequently, it was worth considering for the removal of arsenic from drinking water with arsenic as a new absorbing material for D401-Zr having a perfect removal efficiency to As(V) at relatively low solute levels. 3.6. Thermodynamic Analysis. To describe the thermodynamic behavior of adsorption of arsenic onto D401-Zr, the changes in free energy, ΔG, enthalpy, ΔH, and entropy, ΔS, of

ΔG = −RT ln KL

(6)

T ΔS = ΔH − ΔG

(7)

where ΔG is the standard free energy change, R is the universal gas constant (8.314 kJ·kmol−1·K−1), T is temperature in Kelvin (K), and KL is the Langmuir constant. The standard entropy change (ΔS) and the values of the standard enthalpy change (ΔH) were determined from the intercept and the slope of the Van’t Hoff’s plot of ΔG/T versus 1/T.41 The thermodynamic parameters for the adsorption of arsenic onto D401-Zr at different temperatures were summarized in Table 6. Table 6. Thermodynamic Parameters of As(V) Adsorption onto the D401-Zr at Different Temperatures

431

T/K

KL

ΔG/kJ·mol−1

ΔH/kJ·mol−1

ΔS/J·mol−1·K−1

293 303 313

4.88984 5.71466 8.04109

−3.866325 −4.390953 −5.424626

18.87804

77.35517



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Figures 8 and 9 revealed that the arsenic concentration decreased rapidly and the adsorption capacity of As (mg·g−1) increased with the contact time until the system approached the equilibrium due to the gradual decrease of the driving force (Qe − Qt), which overcame mass-transfer resistance of arsenic between the aqueous and the solid phases. This process was broadly divided into the rapid reaction phase of the beginning and the subsequent slow reaction stage.43 When the concentration of As(V) was below 2 mg·kg−1, it took less than 7 h to reach equilibrium, whereas it took more than 24 h for As(III). In the present study, three kinetic models (the pseudo-firstorder, pseudo-second-order, and the intraparticle diffusion models) were used to describe the As(III) and As(V) adsorption by D401-Zr for evaluating the kinetic mechanism that controlled the adsorption process. The equation corresponding to the pseudo-first-order kinetic model is the following form:44

The Gibbs free energy (ΔG) was negative, which indicated the spontaneous and favorable nature for the adsorption of As(V) onto D401-Zr at (293, 303, and 313) K. The calculated enthalpy (ΔH) value (18.88 kJ·mol−1) showed the endothermic reaction of the adsorption process as was seen earlier with the effect of temperature. The positive values of ΔS (77.36 J·mol−1·K−1) suggested a higher randomness tendency at the solid/solution interface during the adsorption of As(V) on the adsorbent.42 3.7. Effect of Time. The effects of the contact time on the adsorption kinetics of As(III) and As(V) onto D401-Zr are shown in Figures 8 and 9 in terms of the Qt−t relationship.

Q t = Q e[1 − exp( −k1t )]

(8)

The equation about the pseudo-second-order kinetic model is as follows:45 t 1 t = + 2 Qt Q k 2Q e e

(9)

−1

−1

where Qe (mg·g ) and Qt (mg·g ) are the amounts of the adsorbate adsorbed on the adsorbent at equilibrium and at time t (h), respectively. k1 and k2 are the pseudo-first-order rate constant and the pseudo-second-order adsorption rate constant, respectively. As we know, the adsorption is usually governed by either the liquid phase mass transport rate or the intraparticle mass transport rate. Therefore, the experiment data should be analyzed using the intraparticle diffusion model.46

Figure 8. Effect of contact time on the adsorption of As(V) onto the adsorbent (temperature, 293 K; agitation speed, 120 rpm). ▲, 0.5 mg·kg−1; ■, 1.0 mg·kg−1; ●, 2.0 mg·kg−1.

Q t = kdt 1/2 + C

(10)

where kd is the intraparticle diffusion rate constant. If the adsorption mechanism follows the intraparticle diffusion process, a plot of Qt versus t1/2 should be a straight line with a slope kd and intercept C according to eq 7, so the values of kd and C were obtained from the slope of straight lines. The values of parameters of different models were calculated and are listed in Table 7. The results have shown that the experimental data could be fitted well for the pseudo-secondorder (R2 > 0.99) model of the adsorption rate. The calculated Qe values from the model were also in good agreement with the

Figure 9. Effect of contact time on the adsorption of As(III) onto the adsorbent (temperature, 293 K; agitation speed, 120 rpm). ▲, 0.5 mg·kg−1; ■, 1.0 mg·kg−1; ●, 2.0 mg·kg−1.

Table 7. Kinetics Model Parameters of Arsenic Adsorption onto the D401-Zr at Different Initial Arsenic Concentrations C0/mg·kg−1 As(V) model pseudo-first-order

pseudo-second-order

intraparticle diffusion model

As(III)

parameter

0.5

1.0

2.0

0.5

1.0

2.0

Qe1/mg·g−1 k1/h−1 R2 Qe2/mg·g−1 k2/g·(mg·h)−1 R2 kd/mg·(g·h0.5)−1 C R2

0.47617 1.06997 0.97210 0.504465 4.183226 0.99927 0.08022 0.18313 0.64969

0.97179 1.00338 0.98773 1.010193 2.739967 0.99959 0.16049 0.37935 0.62169

1.8102 1.83743 0.91194 1.991556 0.920196 0.99865 0.29652 0.77984 0.65279

0.37910 0.33925 0.96129 0.425058 1.343925 0.99009 0.07753 0.07265 0.89854

0.68429 0.45318 0.95632 0.760682 0.97337 0.99099 0.13421 0.16886 0.84251

1.25375 0.51599 0.91821 1.41229 0.527268 0.99209 0.24368 0.33331 0.84088

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Figure 10. Process of arsenic adsorption onto D401-Zr.

experimental values. As we all know, the pseudosecond-order is based on the assumption that rate limiting step is chemisorption involving valence forces through sharing or exchange of electrons between adsorbate and adsorbent. The adsorption of arsenic may explained that surface exchange reactions until the surface functional sites were all occupied, and then diffused into the adsorbent network for further interaction (Figure 10). First, arsenic transferred across the external boundary layer film of the liquid surrounding the outside of the particle. Second, this step was usually considered to be exceedingly rapid, adsorption at the sites on the surface and the energy depended on the binding process. Lastly, the adsorbate molecules diffused to the adsorption site either by the solid surface diffusion mechanism or by the pore diffusion process through the liquid filled pores. The mechanism of adsorption commonly involves three steps, one or any combination of which can be rate-controlling mechanism.47 3.8. Effect of the Coexisting Anions. The adsorption efficiency of the adsorbent for the removal of arsenic in the treatment of drinking water is usually affected by the presence of various other coexisting anions. Therefore, the influence of different foreign ions (2 mmol·kg−1) toward the adsorption of As(V) (1 mg·kg−1) has been investigated to determine the sensitivity of this method. Generally, drinking water contains more than one anion; common coexisting anions in drinking water include SO42− and Cl−, and sometimes PO43− and F−. Consequently, the presence of those anions may interfere with the removal efficiency of arsenic. In this work, the effect of coexisting SO42−, Cl−, PO43−, and F− on As(V) uptake by D401-Zr resin was determined and is shown in Figure 11. Figure 11 shows the presence of SO42− and Cl− hardly interfered with As(V) adsorption. However, PO43− and F− greatly reduced the adsorption capacity for arsenic, which may be due to the competition for available adsorption sites of the adsorbent between PO43−, F−, and arsenic.

Figure 11. Effect of coexisting anions on As(V) removal precentage (initial As(V) concentration, 1 mg·kg−1; contact time, 24 h; agitation speed, 120 rpm). ●, As(V); ■, As(V) + Cl−; ▲, As(V) + SO42−; ▼, As(V) + F−; ⧫, As(V) + PO43−.

4. CONCLUSIONS In this study, hydrous zirconium oxide-loaded resin (D401-Zr) was prepared based on the carboxylation between carboxyl keys and hydrous zirconium oxide and examined by arsenic adsorption to clarify the effect of hydrous zirconium oxide on the performance of the hybrid adsorbents. The studies on pH dependence, adsorption isotherms, kinetics, and coexisting ions have been conducted for optimization of adsorption conditions of arsenic removal from aqueous solution by D401-Zr. The pH dependence studies demonstrated that D401-Zr had a strong adsorption to As(V) at pH < 5.2, whereas As(III) was well adsorbed between pH 6.3 to 9.2. The adsorption of arsenic was fitted well to the Langmuir isotherm model, which gave the adsorption capacities of the new adsorbent for arsenic removal. The thermodynamics of arsenic adsorption onto D401-Zr resin confirmed the adsorption process was endothermic and spontaneous. The kinetic results show that the pseudosecond order equation fitted the experimental data very well. The 433



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influence of coexisting anions (2 mmol·kg−1) such as SO42− and Cl− on the adsorption process was not clearly. However, PO43− and F− participated in the competition for the binding sites of the adsorbent with arsenic species, accordingly, affecting the removal efficiency.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Funding

This research was funded by the Chinese National Foundation of Natural Sciences (Grant No. 21276027) and the Shandong Provincial Natural Science Foundation, China (Grant No. ZR2010BL028). Notes

The authors declare no competing financial interest.

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Removal of Arsenic from Drinking Water by Using the Zr-Loaded

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