Introduction of an YttriumâManganese Binary Composite That Has

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Introduction of an yttrium-manganese binary composite that has extremely high adsorption capacity for arsenate uptake in different water conditions Yang Yu, Ling Yu, and J. Paul Chen Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie5037098 • Publication Date (Web): 09 Feb 2015 Downloaded from http://pubs.acs.org on February 18, 2015

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Industrial & Engineering Chemistry Research

Introduction of an yttrium-manganese binary composite that has extremely high adsorption capacity for arsenate uptake in different water conditions

Yang Yu, Ling Yu, J. Paul Chen* Department of Civil and Environmental Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore 119260, Singapore ABSTRACT: Arsenic contamination in the natural water has become a global issue due to its high toxicity, accumulation in human body and carcinogenicity. In this study, a new yttrium-manganese binary composite was developed by a one-step co-precipitation method. The mean diameter of the adsorbent was 6.3 µm and the point of zero charge was 7.1. The adsorbent had a chemical formula of Y5Mn6O6(OH)12(CO3)5·5H2O according to the results of the element and functional group from XPS analysis. The FESEM study showed that adsorbent had a loose structure and was composed of nano-sized flakes. The adsorption process was pH-dependent. The removal efficiency of arsenate by the adsorbent was much higher than that of arsenite. The optimal adsorption efficiency of arsenate can be obtained at pH 6.0. The kinetics study showed that adsorption equilibrium of arsenate can be reached within 25 h. The Langmuir model better fitted the experimental data of the adsorption isotherm than Freundlich model. The maximum arsenate adsorption capacity of 279.9-As 1

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mg/g was achieved at pH 7.0, much higher than most reported adsorbents. The presence of fluoride, sulfate, bicarbonate, phosphate and humic acid had a certain influence on the arsenate adsorption, while the adsorption capacity was still above 220 mg-As/g under the maximum concentration of co-existing substance. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that the hydroxyl group on the adsorbent played more important role in the arsenate uptake. 1.

INTRODUCTION

Arsenic contamination in the natural surface water and groundwater has become an important issue of concern in a number of countries, including Argentina, Bangladesh, Canada, China, Chile, Hungary, India, Mexico, Nepal, Thailand, UK, United States, and Vietnam. It has been found that long-term exposure to water contaminated by arsenic even with a low concentration level could cause cancers of skin, lungs, kidneys, bladder, liver and prostate.1 The epidemiological evidences of the arsenic carcinogenicity led to reduce the maximum contaminant level (MCL) of arsenic in the drinking water from 50 to 10 µg/L in 2006 by the United States Environmental Protection Agency (USEPA).2 The stricter standard on the arsenic concentration in drinking water has triggered a series of research to develop cost-effective technologies for the arsenic removal from aqueous solution. The common technologies for arsenic removal include coagulation, precipitation, adsorption, ion-exchange and membrane filtration. Adsorption technology is considered to be one of the better technologies due to its ease in operation. A number of adsorbents have been developed for arsenic removal such as zirconium nanoparticles,3 titanium-iron oxide mixture,4 titanium dioxide impregnated chitosan bead,5 cupric oxide nanoparticle,6 ironcopper bimetal oxide,7 iron-zirconium binary oxide8 and activated carbon.9 However, many 2


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of them only work well in a certain pH range, such as lower pH. Development of costeffective adsorbents, which work well under neutral pH condition, becomes the most important for wider industrial application in treating arsenic contaminated natural water. In recent years, some researches have demonstrated that several rare-earth metals based composites as adsorbents can effectively remove anionic contaminants.10-12 The adsorbents containing such elements as zirconium, titanium, lanthanum and cerium usually perform higher adsorption capacity. More interestingly, the combination of the above rare metal salts together with relatively abundant heavy metal salts (e.g. iron and manganese) reportedly further improves the uptake of anionic contaminants such as arsenic and fluoride.8, 12, 13 It must be emphasized that some of the key elements once being dissolved are toxic. It is therefore extremely important to monitor the concentrations of elements in the water in order that they are far below the regulated levels set by WHO and EPA. Several studies have demonstrated that the leaching of the concerned elements is extremely limited and do not hamper drinking water safety. There are no generally accepted explanations on why the combined metal compounds have better adsorption for the anions. Zhang and coworkers reported higher adsorption of arsenic by a Fe-Ce composite.12 Their quantificational calculation from the XPS narrow scan results of O(1s) spectra demonstrated that the formation of the bimetal composite adsorbent had higher content of hydroxyl (30.8%) than CeO2 and Fe3O4 (12.6% and 19.6%), which played a key role in the enhanced removal of arsenic from aqueous solution. A Fe–Mn binary oxide was developed for enhanced removal of arsenic (As(III) and As(V)).14 The adsorption mechanism was reportedly assumed to be due to a series of redox and adsorption reactions.

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Yttrium behaves similarly to the trivalent rare-earth elements such as lanthanum and cerium; these metal composites work well in adsorption of arsenic.12, 15 A few studies were reported on the applications of yttrium based adsorbents for arsenic removal. Wasay et al. reported that a basic yttrium carbonate was able to remove both arsenite and arsenate from aqueous solution.16 Although the adsorption is much higher than many reported adsorbents, the main concern is that the adsorbent as a metallic carbonate salt can be greatly dissolved under an acidic condition. The arsenic-containing industrial effluent is typically acidic. For example, the pH in arsenic-containing wastewater from a sulfuric acid factory was only 2.17 On the other hand, the pH of arsenic contaminated municipal wastewater is about 8.67.14 It is therefore important to develop adsorbents that can work well in the removal of arsenic in a wider pH range.4, 18 In our preliminary studies, several yttrium based binary metal adsorbents were fabricated for arsenic removal. It was found that an yttrium-manganese binary composite performed well in arsenate removal over a wider pH range. In addition, the adsorbent was stable in both neutral and alkaline environment. Although there was a slight dissolution occurred in acidic condition, high adsorption capacity can be still observed at pH 4. In this study, the novel yttrium-manganese binary composite with high adsorption capacity for the arsenate was first developed through the co-precipitation approach. The structural characteristics of the adsorbent were studied by the field emission scanning electron microscopy (FESEM), the Fourier transform infrared spectroscopy (FTIR) and the X-ray photoelectron spectroscopy (XPS). A series of batch adsorption experiments including adsorption kinetics, isotherm, as well as the influence of solution pH and co-existing substances were studied to better understand the adsorption behavior, by which water 4


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treatment units may be designed. Through the FTIR and XPS studies, the mechanisms for the adsorption were better understood. 2. MATERIAL AND METHODS 2.1 Materials.

The chemicals including Y(NO3)3·6H2O, MnSO4·7H2O, NaOH,

Na2HAsO4·7H2O and As2O3 were of reagent grade and purchased from Sigma-Aldrich. The arsenate stock solution was prepared by dissolving NaHAsO4·7H2O in deionized water, and the working solution was freshly prepared by diluting arsenate stock solution with deionized water. Humic acid sodium salt used in this study was purchased from Sigma-Aldrich. 2.2 Adsorbent preparation. Y(NO3)3·6H2O and MnSO4·7H2O were selected in the fabrication of the adsorbent based on the preliminary study as well as the cost. It is noted that the price of manganese sulfate is only 10% of yttrium nitrate. Yttrium-manganese binary composite with YⅢ: MnⅡ molar ratio of 1:1 was prepared by co-precipitation method. YⅢ and MnⅡ with the total molar concentration of 0.2 M were mixed, and 1 M NaOH was added dropwise to the mixed solution under constant stirring condition until pH 8. The precipitate formed was aged for 6 h at room temperature. The obtained precipitate was filtered and rinsed with deionized water till the conductivity of washing water was similar to that of DI water. The particle was then dried in the oven at 80℃ for 24 h. Finally, the dried material ground into fine powders with the sizes below 200 µm was used in this study. 2.3 Characterization of adsorbent. The surface morphology of the adsorbent was observed by a field emission scanning electron microscope (FESEM) (JSM6700F, JEQ, Japan). The samples were first coated with a thin film of platinum on the surface for electric conductivity. An energy dispersive X-ray spectrophotometer (EDX, JEOL JED 2300) was 5



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used for the surface elemental analysis. The size distribution of the adsorbent was measured by using a laser diffraction instrument (Mastersizer 2000, Malvern, UK) that allowed the measurement of particle sizes ranging from 0.1 to 2000 µm. In the experiment, a certain amount of dried adsorbent was added in DI water and then fully dispersed by ultrasonic device for several minutes. The obtained result was checked by the equipment internal model allowing for weighted residuals ranging from 0.23 to 0.54 %, below 1 % considering the upper limit for good fitting. The point of zero charge (pHpzc) was estimated according to method described by Zhang et al.7 and Kinniburgh et al.19 The Y-Mn binary composite powder was suspended in 0.01 M NaNO3 for 24 h, after which the rate of pH change with time was very slow. 50 ml suspension was then adjusted to various pH values with NaOH or HNO3 solution. After agitation for 60 min for equilibration, the initial pH was measured; 1.5 g NaNO3 was added to each suspension to bring final electrolyte concentration to about 0.45 M. After an additional 3 h, the final pH was measured. The results, plotted as ∆pH (final pH - initial pH) against final pH, yielded the pHpzc as the pH, at which ∆pH equals to 0. 2.4 Adsorption experiments. The adsorption kinetics experiment was carried out at initial arsenate concentration of 30 mg/L, and the solution pH value was controlled at 7.0 during adsorption process by adding a certain amount of NaOH or HNO3. After adsorption experiments, the solution was filtered using 0.45 µm cellulose membrane and arsenate concentration was measured by an inductively coupled plasma optical emission spectrometer (ICP-OES, Perkin-Elmer Optima 3000). In the experiments for pH effect on adsorption, the initial arsenate concentration was 30 6


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mg/L and adsorbent dosage was 0.1 g/L. Solution pH values were controlled from 3 to 10 during the adsorption by adjusting a certain amount of HNO3 and NaOH. The experiment was conducted at room temperature (T = 25 ± 1°C) for 24 h. At the end of experiment, the samples were taken and analyzed for the concentrations. In the adsorption isotherm experiments, 0.01 g adsorbent was added to 100 mL arsenate solutions at the arsenate concentrations from 1 to 100 mg/L. The solution pH was adjusted to 7.0 according to the result from the experiment on pH effect. The solution pH was maintained by adding HNO3 and/or NaOH throughout the adsorption process. Other procedures were the same as that for the pH effect experiment. At such pH and with high arsenic concentration, it was anticipated that the surface functional groups of the adsorbent could fully be utilized, by which the content of adsorption sites was estimated. Co-existing substances of humic acid (HA), NaF, Na2SO4, NaHCO3 and NaH2PO4 were added to solution to investigate the influence of their presence on the arsenate adsorption. The concentrations of co-existing substances were chosen according to typical concentrations in natural groundwater. The concentration range of HA, NaF, Na2SO4, NaHCO3 and NaH2PO4 were 0-10 mg/L, 0-0.5 mM, 0-10 mM, 0-10 mM and 0-0.05 mM, respectively. The mixture solution was prepared by respectively adding co-existing substance into arsenic solution. The concentration of arsenate in the solution was 30 mg/L. Afterwards, 0.1 g/L adsorbent was added and the solution pH during the experiment was controlled at 7. There was no background electrolyte in the experiment in order to avoid the interference of other ions. Other procedures were the same as that for the pH effect experiment. 2.5 Spectroscopic analysis. The FTIR was used to determine the vibration frequency changes in the adsorbent due to the adsorption process. The adsorbents before and after 7



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arsenate adsorption were analyzed by FTIR spectroscopy. The samples were blended with KBr which acted as background at an approximate mass ratio of 1:10 (sample: KBr) and then pressured into a disk for FTIR analysis. The background obtained from scan of pure KBr disk was automatically subtracted from the sample spectra. The scan was taken 3 times in the wavenumber range of 400-4000 cm-1 on a FTS-135 spectrometer (Bio-Rad, USA). The surface of the adsorbents before and after arsenate adsorption was analyzed using an X-ray photoelectron spectroscopy (XPS) (Kratos XPS system – Axis His – 165 Ultra, Shimadzu, Japan), with monochromatized AlKα X-ray source (1486.71 eV) working at 150 W, 15 kV, and 10 mA and the base pressure of 3 × 10-8 Torr in the analytical chamber. The XPS results were collected in binding energy forms and analyzed using a non-linear leastsquare curve fitting program (XPSPEAK41 Software). To compensate for the charging effect, all spectra were calibrated with graphitic carbon as the reference at a binding energy of 284.8 eV. For the elements of yttrium, manganese, carbon and oxygen, the spectra were deconvolved with the subtraction of a linear background and a Gaussian (20%)-Lorentzian (80%) mixed function. The elemental composition of the adsorbent was also measured by XPS spectra with the detection limit of parts per thousand ranges.20 3. RESULTS AND DISCUSSION 3.1 Characterization of adsorbent. The surface morphology of the Y-Mn binary composite is studied by a field emission scanning electron microscope. Figure 1a shows that the adsorbent is aggregated by nano-sized flakes resulting in a high surface area and a loose structure. This structure is obviously beneficial to the transportation of the arsenate to all the active sites of adsorbent. The loose structure of the adsorbent can enhance the internal diffusion of arsenic.21 Based on the analysis of EDX shown in Figure 1b, the adsorbent was 8


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mainly consisted of two elements of yttrium and manganese, and the molar ratio of them would be analysed by XPS to be addressed later. Although the aggregation of the adsorbent occurred after heat drying, the adsorbent as fine powder can be obtained through grinding. The distribution of particle size of the adsorbent is shown in Figure 1c. The particle size of adsorbent is in the range of 1- 20 µm and the mean volume diameter is around 6.3 µm. The value of point of zero charge of adsorbent is approximate 7.1 (Figure 1d). The surface charge of the adsorbent highly depends on the solution pH. If the solution pH is above its pHpzc, the surface of the adsorbent is negatively charged, which would cause stronger electrostatic repulsion between the active sites and the anionic arsenate. On the other hand, the adsorbent becomes positively charged when the solution pH is below its pHpzc, which can lead to better adsorption of arsenate.

9



10

c 8

Volume (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

6 4 2 0 0.01

0.1

1

10

100

Particle size (µm)

10


1000

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0.8

d 0.4

∆pH

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.0 -0.4 -0.8 -1.2 5

6

7

8

9

10

Final pH Figure 1. Characterization of Y-Mn composite: (a) FESEM image, (b) EDX image (c) particle size distribution, and (d) point of zero charge. 3.2 pH effect. The effect of solution pH on the removal of arsenate and arsenite was studied and the result is shown in Figure 2. The adsorption of both arsenate and arsenite is highly pH-dependent. The higher uptake of As(V) occurs in pH ranging from 4 to 7. Less adsorption can be seen at pH < 4 and pH > 9. The maximum adsorption capacity of 272.1 mg-As/g is obtained at pH 6.0. However, the effect of pH on the uptake of As(III) is different from that of As(V); the adsorption increases with an increase in solution pH and reaches its maximum at pH > 9. The As(III) adsorption is about 27 mg-As/g at pH 10. In our previous study,22 it was demonstrated that uptake of arsenite was higher than that of arsenate, mainly due to oxidation of As(III) to As(V) by the MnO2. Figure 2 shows that the adsorbent has a much better affinity for As(V) than As(III). Comparing to our previous finding with that in this study indicates that the oxidation of As(III) to As(V) unlikely occurs.

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The arsenate speciation can be modeled by MINEQL, as shown in Figure S1. H2AsO4- and HAsO42- are the dominant arsenate species in pH ranging from 3 to 10. It is noted that the pHpzc of the adsorbent is 7.1. The stronger protonation of the functional group on the surface of adsorbent can be achieved at pH < 7, which enhances the electrostatic attraction between positively charged active sites of the adsorbent and the arsenate anions. However, with the further increase in solution pH, the surface of the adsorbent may become negatively charged, leading to an enhancement in the electrostatic repulsion effect. As such, the arsenate adsorption decreases at pH > 7.23 It is noted that the uptake of arsenate is quite low at pH 3. It is likely due to the speciation of arsenate species. As shown in Figure S1, H3AsO4 exists as one of dominant species of arsenate. As it carries no charge, the positively charged adsorbent has a very limited effect on the adsorption. Another important reason is that the adsorbent becomes less stable at pH 3 as shown in Figure 3 (to be discussed later). Hence, the adsorption at pH 3 is lower. A higher adsorption capacity of arsenate is found in a wide solution pH range, especially at the neutral pH. This result indicates that our adsorbent is promising in applications in the arsenate removal in natural water as well as contaminated wastewater (pH >4).

12


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350 300

As(V)

a

qe(mg/g)

250 200 150 100 50 0 3

4

5

6

7

8

9

10

pH

35 As(III)

b

30 25

qe(mg/g)

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20 15 10 5 0 2

3

4

5

6

7

8

9

10

11

pH Figure 2. Effect of solution pH on the arsenate (a) and arsenite (b) adsorption: [As(V)]0 = 30 mg/L, [As(III)]0 = 20 mg/L, m = 0.1 g/L, t = 30 h, T= 25 ± 1°C.

13



5

100 Y dissovled in the solution Mn dissolved in the solution Adsorption capacity of arsenate

80

4

60

3

40

2

20

1

0

qe (mmol/g)

Dissolution percentage (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0 2

3

4

5

6

7

8

9

10

11

pH Figure 3. Adsorption capacity of arsenate and the dissolution percentage of Y and Mn under different pH. [As(V)]0 = 30 mg/L, m = 0.1 g/L, t = 30 h, T= 25 ± 1°C. The concentrations of yttrium and manganese in the solution after arsenate adsorption were determined. As shown in Figure 3, the dissolution percentages of Y and Mn (in term of the percentages of Y and Mn dissolved out of total Y and Mn in the adsorbent) highly depend on the solution pH. The adsorbent shows quite stable in both neutral and alkaline conditions and only a slight dissolution is observed until pH 5. Furthermore, the adsorption capacity of the adsorbent at pH 5 is still about 269 mg-As/g, only slightly lower than that at the optimal pH of 6. It is observed that relatively severe dissolution of Y and Mn occurs at more acidic condition which is consistent with the significant reduction of arsenate uptake. Especially at pH 3, the uptake of arsenate by the adsorbent is dropped to only 20 mg/g due to the dissolution of Y and Mn from the adsorbent. Compared with many adsorbents previously reported, more simply equalization of solution pH (just above 5) is required to obtain good 14


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removal efficiency of arsenate and stability of the adsorbent in the field application. 3.3 Adsorption isotherm. Figure 4 demonstrates the adsorption isotherm at pH 7. The adsorption capacity of arsenate is as high as 275 mg-As/g as shown in the diagram. It should be more efficient in the treatment of arsenic rich industrial wastewater. When the initial arsenate concentration is 1 mg/L, the arsenate concentration can be reduced to 80 µg/L under pH 7 and the corresponding adsorption capacity is 4.6 mg/g. It should be noted that some more adsorbent is needed in order that the treated effluent can meet the standard (10 µg/L) in drinking water.

350 300

qe(mg/g)

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250 200 150 100 Experimental data 2 Langmuir isotherm (r = 0.963) 2 Freundlich isotherm (r = 0. 798)

50 0 0

20

40

60

80

C e(mg/L) Figure 4. Adsorption isotherms of arsenate on Y-Mn adsorbent. m = 0.1 g/L, pH = 7.0, t = 30 h, T= 25 ± 1°C. Both Langmuir and Freundlich models were employed to describe the relationship between the amount of arsenate adsorbed and its equilibrium concentration. The typical linear regression approach was used to determine the model parameters. 15



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The transformation of non-linear isotherm equations to linear forms alters their error structure and may also violate the error variance and normality assumptions of standard least squares. Therefore, it is necessary to analyze the data using the non-linear chi-square test (χ2) in order to validate an appropriate isotherm. χ2 is determined as the following equation:

χ2 = ∑

( q e − q e ,m ) 2

(1)

qe ,m

where qe is the experimental equilibrium uptake (mg/g) and qe,m is the equilibrium uptake (mg/g) calculated using the model. The results of the linear regression analysis and the non-linear chi-square test analysis are given in Table 1. The obtained results from χ2 test are in agreement with those from the r2 values from the linear regression. The study from both approaches clearly indicates that the Langmuir model fits the experimental data better than Freundlich model, indicating that the arsenate uptake is due to the monolayer adsorption.24, 25 The maximum adsorption capacity of arsenate calculated by the below Langmuir model is 279.9 mg-As/g under neutral pH condition (pH = 7.0). The molecular weight of arsenic element is 75 g/mol. Based on the calculation, the reaction sites present in adsorbent are 3.732 mmol/g under neutral pH condition. As compared with the adsorption capacities given in Table 2, we can conclude that the adsorption capacity of the adsorbent reported in this paper is much higher than those of the reported adsorbents.3, 4, 26, 27

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Table 1. Langmuir and Freundlich isotherms for the arsenate adsorption. Regression approach

Langmuir isotherm

Freundlich isotherm

qmax (mg/g)

b (L/mg)

r2

χ2

Kf (L/g) n

r2

χ2

Linear

270.3

1.057

0.999

-

94.62

3.086

0.612

-

Non-linear

279.9

2.746

0.963

51.31

144.9

5.563

0.798

147.1

The adsorbent can be directly used for treating arsenic containing industrial and municipal wastewater. Due to the extremely high efficiency, it is anticipated that much smaller dosage is needed for the water and wastewater treatment. The used adsorbent can be regenerated with water at pH > 12 according to Figure 2. The concentrated arsenic can be collected for industrial use (e.g. LCD production). In the event that the spent adsorbent is mixed with solids (like the SS in surface water treatment), the regeneration would become less meaningful. It is therefore recommended that the spent adsorbent be landfilled in a strictly control area. Table 2. Comparison of maximum arsenate adsorption of different adsorbentsa. Adsorbent

Max. adsorption capacity (mg/g) a 82.7 (pH 7.0)

Ref.

Fe-Cu binary oxide

Arsenic conc. (mg/L) 0-50

Fe-Mn binary oxide

0-40

53.9 (pH 7.0)

28

Fe-Zr binary oxide

0-40

46.1 (pH 7.0)

8

Zr based nanoparticle

0-80

256.4 (pH 3.0)

3

Mg-Al layered double hydroxide NHITO

0-150

129.7 (pH 5.0)

29

5-250

14.3 (pH 7.0)

30

1-40

32.2 (pH 7.0)

31

0-100

279.9 (pH 7.0)

Present study

Fe3O4 coated boron nitrite nanotube Y-Mn binary composite a

pH is shown in parentheses. 17


7


3.4 Adsorption Kinetics. Figure 5 shows that about 75% of equilibrium adsorption capacity is achieved at the first 7 h under the initial arsenate concentration of 30 mg/L. Subsequently, the arsenate adsorption slows down and the equilibrium can be reached within 25 h.

300 250

qe(mg/g)

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200 150 100 Experimental data Pseudo-first-order equation Pseudo-second-order equation

50 0 0

5

10

15

20

25

30

35

Time (h) Figure 5. Adsorption kinetics of arsenate. [As(V)]0 = 30 mg/L, m = 0.1 g/L, pH = 7.0, T= 25 ± 1°C. To better understand the adsorption mechanism, pseudo first- and second-order models are employed to simulate the adsorption process. The pseudo first-order model is generally expressed as below: ln(q e − qt ) = ln q e − k1t

(2)

The pseudo second-order model is based on the assumption that the rate of occupation of 18


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adsorption sites is proportional to the square of the number of unoccupied sites and can be described as the following form:

t 1 t = + 2 qt k 2 qe q e

(3)

where qe and q t are the amount of arsenate adsorbed by adsorbent at equilibrium and time t (mg/g), k1 (h-1) and k 2 (g·mg-1·h-1) the equilibrium constant of the pseudo-first and pseudosecond models, respectively. t is the adsorption time (h). As shown in Figure 5, the experimental data are analyzed by both models. By comparing with the related parameters listed in Table 3, the experimental data can be better described by the pseudo-second-order model with the higher value of correlation coefficient (r2 = 0.99). Table 3. Parameters of pseudo-first and -second order equations ([As]0 = 30 mg/L). Pseudo-first-order

Pseudo-second-order

qe (mg/g)

k1 (h-1)

r2

qe (mg/g)

k2 (gmg-1h-1)

r2

271.33

0.25

0.97

282.23

0.001

0.99

3.5 Effect of co-existing competing substances. Anions such as fluoride, sulfate, bicarbonate, phosphate generally co-exist in natural water.32,

33

They may compete with

arsenate ions for the active sites. The HA compounds are the most important among natural organic matters. The HA well exists in arsenic contaminated surface water and groundwater. Being anionic, it would compete with arsenic for the adsorption sites on the adsorbent. In addition, the presence of HA may cause fouling on the adsorbent, which would reduce the adsorption capability. Therefore, it is significant to investigate the influence of HA on the 19



adsorption of arsenate. Figure 6 demonstrates that the effect of the presence of the co-existing anions and humic acid on the uptake of arsenate on the adsorbent. The concentration ranges of co-existing substances are chosen according to their typical concentrations in natural groundwater. There is no obvious interference observed in the presence of these co-existing substances. Only 10% to 14% reduction in the amount of arsenate adsorbed is observed for all the investigated co-existing substances under their highest concentration. The adsorption capacity is still above 220 mg-As/g due to higher affinity of functional groups on the adsorbent for the arsenate. 280

240

qe(mg/g)

200

160

-

HCO3

2-

SO4

3-

PO4

F

0m 2 mg/L 4 mg/L 6 mg/L 8 g/L 10 mg/L mg /L

0 0.1 mM 0.2 mM 0.3 mM 0.4 mM 0.5 mM mM

0.00 mM 0.01 mM 0.02 mM 0.03 mM 0.04 mM 5m M

0m 2 mM 4 mM 6 mM 8 M 10 mM mM

120 0m 2 mM 4 mM 6 mM 8 M 10 mM mM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

-

HA

Figure 6. Effects of co-existing ions and humic acid on As(V) adsorption. [As(V)]0 = 30 mg/L, m = 0.1g/L, pH = 7.0, t = 30 h, T= 25 ± 1°C. 3.6 Spectroscopic analysis. The transmission FTIR spectrum of virgin and As-loaded adsorbents is shown in Figure 7. The appearance of two additional peaks in the spectrum after 20


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arsenate adsorption at 825 and 866 cm-1 is assigned to the vibration of As-O for adsorbed arsenate species in the form of the monodentate complex (M-O)AsO3- and bidentate complex (M-O)2AsO2, respectively.34

(a) As-loaded adsorbent (b) Virgin adsorbent

1078 947 866 849 825 1509 1395

1633

(b)

3408

1633 1522 1387

(a)

3415

Transmittance(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4000

3500

3000

2500

2000

1500

1000

500

-1

Wave Number(cm ) Figure 7. FTIR spectra of Y-Mn adsorbents before and after arsenate adsorption. The broad band at around 3400 cm-1 can be attributed to O-H stretching vibrations due to surface and interlayer adsorbed water, while the band at 1633 cm-1 may be assignable to the blending vibration of the physically adsorbed water.35 The two peaks at 1509 and 1395 cm-1 in the virgin adsorbent might be attributed to the vibration of carbonate group, since the solution is open to the air during the preparation of adsorbent.36 After adsorption, these two peaks remarkably decreases, which may result from the reason that the carbonate group participates in the arsenic uptake (to be discussed later again). The bands at 849, 947 and 1078 could be attributed to the stretching mode of hydroxyl group (M-OH)37 and the intensity of the peaks also nearly disappears after the arsenate adsorption. This observation implies that the replacement of the –OH group may occur in the 21



arsenate uptake process. Similar phenomenon has been reported by many studies.8, 10, 38 XPS was used to further determine the interaction of arsenate on the adsorbent. The XPS wide scan spectra of the virgin and As-loaded adsorbents are shown in Figure 8. The presence of the As3d, As3p, As3s and AsLMM peaks in the As-loaded adsorbent clearly indicates arsenate has been successfully adsorbed onto the adsorbent. The high resolution XPS spectrum of As3d of the arsenate-loaded adsorbent is shown in Figure S 2. It can be seen that the As3d peak at 45.5 eV is assigned to As (V).39

(a) Virgin adsorbent

O1s OK L1

M n2p

M nLM 2

C1s Y3p

Y3d

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

M n3p

(b) As-loaded adsorbent

O 1s OK L1

M n2p C1s

M nLM 2

A sLM M Y3d A s3p A s3s M n3p A s3d

0

200

Y3p

400

600

800

1000

B inding E nergy (eV )

Figure 8. XPS wide-scan spectra of the adsorbents: (a) virgin adsorbent; (b) As-loaded adsorbent. The oxidation states of the yttrium and manganese in the adsorbent are examined and shown in Figure 9. The peak positions of Y 3d5/2 and Y 3d3/2 are characteristic of Y(III). The Mn 2p spectrum of the adsorbent is divided by three peaks with the binding energies of 22


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641.5, 642.2 and 643.4 eV, which are assigned to Mn(II), Mn(III) and Mn(IV), respectively. According to their relative ratios, the manganese in the adsorbent is mainly in the oxidation state of +IV.

a Intensity

Y 3d5/2 Y 3d3/2

154

156

158

160

162

164

Binding Energy (eV)

b Mn(III) 29.75%

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Mn(IV)

Mn(II)

43.20%

27.05%

638

640

642

644

646

Binding Energy (eV) Figure 9. XPS spectra of the adsorbent: (a) Y 3d, and (b) Mn 2p3/2.

23


648


To further confirm the role of carbonate group, C 1s spectra of the adsorbents before and after adsorption are investigated and shown in Figure 10. The main absorption is found at the binding energy of 284.8 eV namely as reference carbon due to exposure to the atmosphere. Meanwhile, the peak with the binding energy of 289.43 eV is attributed to the presence of carbonate group.40 After arsenic adsorption, the strength of this peak decreases and the relative ratio drops from 15.11% to 5.2%. The exchange between carbonate group and arsenate might also offer some certain contribution to the high uptake of arsenic. Wasay et al. used a basic yttrium carbonate to remove both arsenite and arsenate from aqueous solution.16 In the study, the release of carbonate ion depends on the adsorption of arsenate.

(a) Virgin adsorbent Reference C 1s 84.89% 2-

CO 3

15.11%

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(b) As-loaded adsorbent Reference C 1s 94.80% 2-

CO 3

5.20%

280

282

284

286

288

290

292

294

Binding Energy (eV)

Figure 10. XPS spectra of C 1s of the adsorbents: (a) virgin adsorbent; (b) As-loaded adsorbent. As shown in Figure 11, the high resolution scan of O1s spectrum of the adsorbents can be 24


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divided into metal oxide (M-O), hydroxyl group bonded to metal (M-OH) and carbonate group (-CO32-) and adsorbed water (H2O) with the binding energies of 529.93, 531.43 and 532.89 eV (for virgin adsorbent) and 530.00, 531.21 and 532.89 eV (for As-loaded adsorbent).

(a) Virgin adsorbent 2-

M -O H, -C O 3 69.43%

M -O

H 2O

17.77%

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


12.80%

(b) As-loaded adsorbent 2-

M -O H, -C O 3 58.30%

M -O

H 2O

19.46%

22.24%

528

530

532

534

536

Binding Energy (eV )

Figure 11. XPS spectra of O 1s of adsorbents: (a) virgin adsorbent; (b) As-loaded adsorbent. After the arsenate adsorption, the relative area ratios for the peaks due to the M-O and H2O increase from 17.77% to 19.46% and 12.80% to 22.24%, respectively. The relative area ratio for the peak due to M-OH and -CO32- decreases from 69.43% to 58.30%. The decrease in the area ratio clearly indicates that the hydroxyl group and carbonate group on the adsorbent surface participates in the arsenate adsorption. The amount of carbonate group in the adsorbent is considered limiting since it only comes from the atmosphere. Thus, the hydroxyl group on the surface of the adsorbent plays more important role in arsenic uptake. 25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 34

The atomic ratios of Y, Mn, C, O and As in the adsorbents before and after adsorption are shown in Table 4. The atomic fraction of arsenic on the surface of the adsorbent is increased from 0% to 3.54% after adsorption. This indicates that the arsenate can be adsorbed onto the composite. Meanwhile, the atomic faction of O decreases remarkably from 41.64% to 34.27% after the adsorption, which might result from the replacement of hydroxyl groups and carbonate group on the surface of the adsorbent with the arsenate ions in the adsorption process. Based on the data of atomic percentages in Table 4 and the percentages of oxygencontaining groups and carbonate group from XPS analysis, the chemical formula of the adsorbent can be deduced as Y5Mn6O6(OH)12(CO3)5·5H2O. Table 4. Atomic ratios in the adsorbents from XPS study. Atomic ratio (%)

Y

Mn

C

O

As

Virgin adsorbent

6.26

7.25

44.85

41.64

0

As-loaded adsorbent

5.48

6.02

50.70

34.27

3.54

From the result of pH effect and analysis of FTIR and XPS, the mechanism of arsenic removal by the adsorbent can be described in Figure 12. The arsenic adsorption is controlled by the formation of surface complexes through the replacement of hydroxyl group and carbonate group with the arsenic ions. Meanwhile, the adsorption process is affected by the electrostatic interactions to some extent.

26


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 12. Schematic diagram of adsorption mechanism of arsenate: a) solution pH < pHpzc; b) solution pH > pHpzc. 4. CONCLUSIONS The Y-Mn binary composite adsorbent was successfully developed by co-precipitation method. The XPS analysis indicated that the estimated chemical formula of the adsorbent was Y4Mn5O5(OH)14(CO3)4·4H2O. The FESEM study showed that the fabricated adsorbent was aggregated by nano-size flakes and had a loose structure. The adsorbent had a mean diameter of 6.3 µm, and the pHpzc of the adsorbent was around 7.1. The pH impact study revealed the arsenate adsorption was pH-dependent and the optimal pH for arsenate adsorption was 6.0. The adsorption isotherm study showed that the maximum adsorption capacity at pH 7 could reach 279.9 mg-As/g. The adsorption equilibrium was established within 25 h. The presence of fluoride, sulfate, bicarbonate, phosphate and humic acid had less impact on the adsorption 27



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Page 28 of 34

of arsenate. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis indicated that -OH group on the surface of the adsorbent might play more important role in the arsenate adsorption.

AUTHOR INFORMATION Corresponding Author *

Tel.:

+65-6516-8092.

Fax:

+65-6774-4202.

Email:

[email protected];

[email protected].

ACKNOWLEDGEMENT The authors are grateful for the financial supports from National

Research

Foundation

Singapore (NRF2011NRF-POC001-028). YY and LY would like to thank Singapore-PekingOxford Research Enterprise providing PhD scholarship under Grant No. COY-15-EWIRCFSA/N197-1.

Supporting Information Available: The distribution of arsenate species at different pH levels. This material is available free of charge via the internal at http://pubs.acs.org/. REFERENCES (1) Karim, M. M. Arsenic in Groundwater and Health Problems in Bangladesh. Water Res. 2000, 34, 304-310.

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(2) Vrijenhoek, E. M.; Waypa, J. J. Arsenic Removal from Drinking Water by a “Loose” Nanofiltration Membrane. Desalination 2000, 130, 265-277. (3) Ma, Y.; Zheng, Y.-M.; Chen, J. P. A Zirconium Based Nanoparticle for Significantly Enhanced Adsorption of Arsenate: Synthesis, Characterization and Performance. J. Colloid Interface Sci. 2011, 354, 785-792. (4) Patra, A. K.; Dutta, A.; Bhaumik, A. Highly Ordered Mesoporous TiO2–Fe2O3 Mixed Oxide Synthesized by Sol–Gel Pathway: An Efficient and Reusable Heterogeneous Catalyst for Dehalogenation Reaction. ACS Appl. Mater. Interfaces 2012. (5) Miller, S. M.; Zimmerman, J. B. Novel, Bio-Based, Photoactive Arsenic Sorbent: TiO2-Impregnated Chitosan Bead. Water Res. 2010, 44, 5722-5729. (6) Reddy, K. J.; McDonald, K. J.; King, H. A Novel Arsenic Removal Process for Water Using Cupric Oxide Nanoparticles. J. Colloid Interface Sci. 2013, 397, 96-102. (7) Zhang, G.; Ren, Z.; Zhang, X.; Chen, J. Nanostructured Iron(III)-Copper(II) Binary Oxide: A Novel Adsorbent for Enhanced Arsenic Removal from Aqueous Solutions. Water Res. 2013, 47, 4022-4031. (8) Ren, Z.; Zhang, G.; Paul Chen, J. Adsorptive Removal of Arsenic from Water by an Iron–Zirconium Binary Oxide Adsorbent. J. Colloid Interface Sci. 2011, 358, 230-237. (9) Asadullah, M.; Jahan, I.; Ahmed, M. B.; Adawiyah, P.; Malek, N. H.; Rahman, M. S. Preparation of Mcroporous Activated Carbon and Its Modification for Arsenic Removal from Water. J. Ind. Eng. Chem. 2014, 20, 887-896.

29



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(10) Cui, H.; Li, Q.; Gao, S.; Shang, J. K. Strong Adsorption of Arsenic Species by Amorphous Zirconium Oxide Nanoparticles. J. Ind. Eng. Chem. 2012, 18, 1418-1427. (11) Tokunaga, S.; Wasay, S. A.; Park, S.-W. Removal of Arsenic(V) Ion from Aqueous Solutions by Lanthanum Compounds. Water Sci. Technol. 1997, 35, 71-78. (12) Zhang, Y.; Yang, M.; Dou, X.-M.; He, H.; Wang, D.-S. Arsenate Adsorption on an Fe−Ce Bimetal Oxide Adsorbent: Role of Surface Properties. Environ. Sci. Technol. 2005, 39, 7246-7253. (13) Yu, Y.; Chen, J. P. Fabrication and Performance of a Mn-La Metal Composite for Remarkable Decontamination of Fluoride. J. Mater. Chem. A 2014, 2, 8086-8093. (14) Wu, K.; Wang, H.; Liu, R.; Zhao, X.; Liu, H.; Qu, J. Arsenic Removal from a HighArsenic Wastewater Using in Situ Formed Fe–Mn Binary Oxide Combined with Coagulation by Poly-Aluminum Chloride. J. Hazard. Mater. 2011, 185, 990-995. (15) Li, Z.; Deng, S.; Yu, G.; Huang, J.; Lim, V. C. As(V) and As(III) Removal from Water by a Ce–Ti Oxide Adsorbent: Behavior and Mechanism. Chem. Eng. J. 2010, 161, 106-113. (16) Wasay, S. A.; Haron, M. J.; Uchiumi, A.; Tokunaga, S. Removal of Arsenite and Arsenate Ions from Aqueous Solution by Basic Yttrium Carbonate. Water Res. 1996, 30, 1143-1148. (17) Wang, H.-J.; Gong, W.-X.; Liu, R.-P.; Liu, H.-J.; Qu, J.-H. Treatment of High Arsenic Content Wastewater by a Combined Physical–Chemical Process. Colloids Surf., A 2011, 379, 116-120.

30


Page 30 of 34

Page 31 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(18) Wu, K.; Liu, T.; Xue, W.; Wang, X. Arsenic(III) Oxidation/Adsorption Behaviors on a New Bimetal Adsorbent of Mn-Oxide-Doped Al Oxide. Chem. Eng. J. 2012, 192, 343-349. (19) Kinniburgh, D.; Syers, J.; Jackson, M. Specific Adsorption of Trace Amounts of Calcium and Strontium by Hydrous Oxides of Iron and Aluminum. Soil Sci. Soc. Am. J. 1975, 39, 464-470. (20) Watts, J. F.; Wolstenholme, J. In An Introduction to Surface Analysis by XPS and AES. John Wiley & Sons, 2005, pp i-xi. (21) Hui, B.; Zhang, Y.; Ye, L. Structure of PVA/Gelatin Hydrogel Beads and Adsorption Mechanism for Advanced Pb(II) Removal. J. Ind. Eng. Chem. 2014. (22) Zhang, G.; Khorshed, A.; Paul Chen, J., Simultaneous Removal of Arsenate and Arsenite by a Nanostructured Zirconium–Manganese Binary Hydrous Oxide: Behavior and Mechanism. J. Colloid Interface Sci. 2013, 397, 137-143. (23) Zheng, Y.-M.; Lim, S.-F.; Chen, J. P. Preparation and Characterization of ZirconiumBased Magnetic Sorbent for Arsenate Removal. J. Colloid Interface Sci. 2009, 338, 22-29. (24) Song, X.; Zhang, Y.; Yan, C.; Jiang, W.; Chang, C. The Langmuir Monolayer Adsorption Model of Organic Matter into Effective Pores in Activated Carbon. J. Colloid Interface Sci. 2013, 389, 213-219. (25) Langmuir, I. The Adsorption of Gases on Plane Surfaces of Glass, Mica and Platinum. J. Am. Chem. Soc. 1918, 40, 1361-1403. (26) Luo, X.; Wang, C.; Luo, S.; Dong, R.; Tu, X.; Zeng, G. Adsorption of As (III) and As 31



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(V) from Water Using Magnetite Fe3O4-Reduced Graphite Oxide–MnO2 Nanocomposites. Chem. Eng. J. 2012, 187, 45-52. (27) Patra, A. K.; Dutta, A.; Bhaumik, A. Self-Assembled Mesoporous γ-Al2O3 Spherical Nanoparticles and Their Efficiency for the Removal of Arsenic from Water. J. Hazard. Mater. 2012, 201–202, 170-177. (28) Zhang, G.-S.; Qu, J.-H.; Liu, H.-J.; Liu, R.-P.; Li, G.-T. Removal Mechanism of As(III) by a Novel Fe−Mn Binary Oxide Adsorbent: Oxidation and Sorption. Environ. Sci. Technol. 2007, 41, 4613-4619. (29) Wen, T.; Wu, X.; Tan, X.; Wang, X.; Xu, A. One-Pot Synthesis of Water-Swellable Mg–Al Layered Double Hydroxides and Graphene Oxide Nanocomposites for Efficient Removal of As(V) from Aqueous Solutions. ACS Appl. Mater. Interfaces 2013, 5, 3304-3311. (30) Gupta, K.; Ghosh, U. C. Arsenic Removal Using Hydrous Nanostructure Iron(III)– Titanium(IV) Binary Mixed Oxide from Aqueous Solution. J. Hazard. Mater. 2009, 161, 884892. (31) Chen, R.; Zhi, C.; Yang, H.; Bando, Y.; Zhang, Z.; Sugiur, N.; Golberg, D. Arsenic (V) Adsorption on Fe3O4 Nanoparticle-Coated Boron Nitride Nanotubes. J. Colloid Interface Sci. 2011, 359, 261-268. (32) Li, T.; Zhu, Z.; Wang, D.; Yao, C.; Tang, H. Characterization of Floc Size, Strength and Structure under Various Coagulation Mechanisms. Powder Technol. 2006, 168, 104-110. (33) Paramasivam, S.; Alva, A. K. A Comparison of Anion Concentration in Surficial Groundwater Sampled from Two Types of Water Quality Monitoring Wells. J. Environ. Sci. 32


Page 32 of 34

Page 33 of 34

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Health, Part A: Toxic/Hazard. Subst. Environ. Eng. 2007, 42, 45-50. (34) Guan, X.-H.; Wang, J.; Chusuei, C. C. Removal of Arsenic from Water using Granular Ferric Hydroxide: Macroscopic and Microscopic Studies. J. Hazard. Mater. 2008, 156, 178185. (35) Li, F. Layer-by-Layer Loading Iron onto Mesoporous Silica Surfaces: Synthesis, Characterization and Application for As(V) Removal. Microporous Mesoporous Mater. 2013, 171, 139-146. (36) Aghazadeh, M.; Hosseinifard, M.; Peyrovi, M. H.; Sabour, B. Electrochemical Preparation and Characterization of Brain-Like Nanostructures of Y2O3. J. Rare Earths 2013, 31, 281-288. (37) Lǚ, J.; Liu, H.; Liu, R.; Zhao, X.; Sun, L.; Qu, J. Adsorptive Removal of Phosphate by a Nanostructured Fe–Al–Mn Trimetal Oxide Adsorbent. Powder Technol. 2013, 233, 146154. (38) Tang, W.; Su, Y.; Li, Q.; Gao, S.; Shang, J. K. Superparamagnetic Magnesium Ferrite Nanoadsorbent for Effective Arsenic (III, V) Removal and Easy Magnetic Separation. Water Res. 2013, 47, 3624-3634. (39) Zhang, S.; Li, X.-y.; Chen, J. P. Preparation and Evaluation of a Magnetite-Doped Activated Carbon Fiber for Enhanced Arsenic Removal. Carbon 2010, 48, 60-67. (40) Heuer, J. K.; Stubbins, J. F. An XPS Characterization of FeCO3 Films from CO2 Corrosion. Corros. Sci. 1999, 41, 1231-1243.

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