Preparation and Regeneration of Composite of Cationic gel and Iron Hydroxide for Adsorbing Arsenic from Ground Water

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1 Preparation and Regeneration of Composite of Cationic gel and Iron Hydroxide for Adsorbing Arsenic from Ground Water Syed Ragib SAFI *, Takehiko GOTOH *, Takashi IIZAWA * and Satoshi NAKAI * * Department of Chemical Engineering, Hiroshima University, Kagamiyama, Higashi Hiroshima, Hiroshima, Japan ( m176687@hiroshima-u.ac.jp; tgoto@hiroshima-u.ac.jp) Abstract Arsenic is lethal to human health. It is a serious health concern in many countries, mostly in Bangladesh and India. Currently, Iron hydroxide is used to remove Arsenic, but the amount of adsorption is low and also additional separation processes are required, resulting in high cost. In order to remove Arsenic more effectively from groundwater, to ensure selective adsorption, to simplify the process and to reduce cost, a new gel composite is prepared by combining a polymer cationic gel, N,N -dimethylamino propylacrylamide, methyl chloride quaternary (DMAPAAQ) and Iron(III) Hydroxide (FeOOH) particles. This gel composite adsorbs arsenic better than iron hydroxide and non-ionic gels. Its selective adsorption property is also better than the ionic and non-ionic gels. It has reusability, which makes it more economic. Hence, DMAPAAQ+FeOOH provides better arsenic adsorption, selectivity of arsenic, process simplification and cost reduction; which will make arsenic removal easier, cheaper and more convenient. Keywords Arsenic; adsorption; gel; Iron hydroxide; groundwater; polymer; regeneration INTRODUCTION Arsenic (As) poisoning in drinking water threatens more than 150 million people in the world. Consumption of Arsenic directly or indirectly, may be lethal to human health. The permissible limit of Arsenic in drinking water set by World Health Organization (WHO) is less than 0.01mg/L. However, this limit is exceeded in the groundwater in various parts of the world including USA, China, Chile, Bangladesh, Taiwan, Mexico, Argentina, Poland, Canada, Hungary, Japan and India etc. Among twenty one countries in different parts of the world affected by groundwater arsenic contamination, the largest population at risk is in Bangladesh followed by West Bengal in India (D. Mohan et al., 2007). Particularly in Bangladesh, arsenic contained in minerals from the Himalayas flows into groundwater and about half of the wells in the country exceed the standard value. WHO deemed the arsenic in Bangladeshi groundwater to be the largest mass poisoning of a population in history (R. Singh et al., 2015). To improve this situation, establishing arsenic removal technology is urgently required. Currently, coagulation precipitation method using ferric chloride and iron hydroxide adsorption method is mostly used. However, there is poor adsorption and additional processes such as separation of precipitate and filtration of the adsorbent. Therefore, in order to improve the amount of Arsenic adsorption and selectivity, and to ensure easy handling or process simplicity, N,N-dimethylamino propylacrylamide, methyl chloride quaternary (DMAPAAQ) and Iron(III) Hydroxide (FeOOH) particles, a cationic gel composite, is prepared. When it is put into water, the gel swells and its surface area increases to adsorb Arsenic. Inside the gel, a cationic charge adsorbs Arsenic and Iron Hydroxide improves the selective adsorption.

2 Additionally, the gel composite can be regenerated. Therefore, cost will be less than the currently used methods. EXPERIMENTAL Materials The monomer, N,N -dimethylamino propylacrylamide, methyl chloride quaternary (DMAPAAQ) and N,N - dimethyl acrylamide (DMAA) was supplied by KJ Chemicals Corporation, Japan. The Crosslinker, N,N -Methylene bisacrylamide (MBAA) was supplied by Sigma-Aldrich, USA. Sodium Sulfite(Na2SO3), Di-Sodium Hydrogenarsenate Heptahydrate(Na2HAsO4.7H20) and Ferric Chloride(FeCl3) was supplied by Nacalai Tesque, Inc., Japan. Sodium Hydroxide(NaOH) was supplied by Kishida Chemicals Corporation, Japan. Ammonium peroxodisulfate (APS) was supplied by Kanto Chemical Co. Inc., japan. Preparation of the gel composite The Cationic gel composite was prepared by using DMAPAAQ as Monomer, MBAA as crosslinker. Additionally, Sodium Hydroxide and Ferric Chloride was added to Monomer and Initiator solutions respectively, so that the following reaction takes place: FeCl3+3NaOH Fe(OH)3+3NaCl. The detailed composition is shown in Table 1. After the gel composite is formed, it is cut into cubic shape of 5mm in length. Then, they are washed by distilled water for 24 hours. Lastly, they are dried in the oven at 50 C for 24 hours. To evaluate the arsenic adsorption property, a composite was formed using N,N -dimethyl acrylamide (DMAA) and FeOOH, which is nonionic, for comparison purpose. Measurement of arsenic adsorption property by the gel composite To adsorb Arsenic, 20 mg of dried gel was added in 40 ml of Na2HAsO4.7H20 solution and was kept in the stirrer at 120rpm rotation, at 20 C for 24 hours. While experimenting the selectivity of Arsenic, the same amount of dried gel was added to 40mL solution, containing 0.2mmol/L Na2HAsO4.7H20 and different concentrations of NaCl, 20 ml each. To measure the adsorbed and desorbed amount of Arsenic, High Profile Liquid Chromatography (HPLC) Dionex 1100 ICX by Thermo Fisher Scientific Inc., MA, USA, was used. Water used in all experiments was prepared in a water purification system. ph/orp meter D-72 was supplied by Horiba Scientific, Japan. Regeneration experiment of gel composite While experimenting the regeneration of the gel composite, during adsorption, Arsenic concentration was 0.2mmol/L. And for desorption, 0.5mol/L NaCl was used. The experiment was continued for eight days and the same gel composite was used throughout the experiment. ph of the solution was measured before and after adsorption and desorption.

3 Amount of Arsenic Adsorption [mmol/gadsorbent] Table 1. Composition of gel composite. Chemical Quantity (mol/m 3 ) Monomer DMAPAAQ, DMAA 375 Crosslinker MBAA 50 Accelerator Sodium Sulfite 80 Sodium Hydroxide (NaOH) 2100 Initiator Ammonium peroxodisulfate (APS) 30 Ferric Chloride (FeCl3) 700 RESULTS AND DISCUSSION Amount of arsenic adsorption and it s mechanism Fig. 1 shows the arsenic adsorption isotherms for DMAPAAQ, DMAPAAQ+FeOOH, DMAA+FeOOH and -FeOOH; and the comparison of the amount of their arsenic adsorption. In addition, the experimental value is compared with the calculated value from the adsorption isotherm equation of Langmuir. DMAPAAQ+FeOOH adsorbs arsenic better than DMAA+FeOOH and -FeOOH, and slightly less than DMAPAAQ. Then we examined whether it was chemisorption or physical adsorption. And, the maximum capacity of arsenic adsorption, Qmax, is calculated from the adsorption isotherm of Langmuir (Table 2). After comparing the data with the experimental values, it matches well with DMAPAAQ+FeOOH, DMAA+FeOOH, - FeOOH and DMAPAAQ gel. Therefore, the adsorption of arsenic appears to be chemisorption, due to the ionic interaction with amino group (DMAPAAQ) and adsorption with iron hydroxide DMAPAAQ+FeOOH γ-feooh DMAA+FeOOH DMAPAAQ Adsorption period: 24hr Temperature: 20 Volume of As: 40ml Gel weight: 20mg Langmuir Isotherm Equilibrium Arsenic Concentration [mmol/l] Fig. 1 Arsenic adsorption isotherm

(DMAPAAQ+FeOOH) (Fig. 2). The amount of Arsenic adsorption of DMAPAAQ+FeOOH is moderate. In the real-life scenario, the concentration of Arsenic is lower.

-FeOOH because of the ion exchange phenomena. Table 2. Maximum Adsorption of Arsenic by Langmuir Adsorption Isotherm equation Qmax [mmol/g] ([mg/g]) R 2 DMAPAAQ+FeOOH 1.

Yanagita, 2013) From the above, it was found that adsorption of the composite of DMAPAAQ and iron is chemisorption.

4 (DMAPAAQ+FeOOH) (Fig. 2). The amount of Arsenic adsorption of DMAPAAQ+FeOOH is moderate. In the real-life scenario, the concentration of Arsenic is lower. At such low concentration, the adsorption performance of the cationic gels like DMAPAAQ and DMAPAAQ+FeOOH is closer and better than that of the non-ionic gel DMAA+Fe and -FeOOH because of the ion exchange phenomena. Table 2. Maximum Adsorption of Arsenic by Langmuir Adsorption Isotherm equation Qmax [mmol/g] ([mg/g]) R 2 DMAPAAQ+FeOOH 1.00(75.17) DMAPAAQ 1.26(94.58) FeOOH 0.59(44.32) DMAA+FeOOH 0.31(23.57) Iron Hydroxide (56.8) (T. Yanagita, 2013) From the above, it was found that adsorption of the composite of DMAPAAQ and iron is chemisorption. When DMAPAAQ is added to Arsenic solution, Cl - counters ion with the amino group of DMAPAAQ (Fig. 2) The Cl - is then released into the solution and Arsenic is adsorbed Fig. 2 Mechanism of Arsenic adsorption in DMAPAAQ gel and DMAPAAQ+FeOOH gel composite Fig. 3 Selective adsorption of Arsenic

by DMAPAAQ. In the case of DMAPAAQ+FeOOH, besides Cl -, FeOOH also exchanges ion with Arsenic. That's why the Cl - released into solution is less than that of DMAPAAQ.

7H20, the selectivity of Arsenic adsorption of DMAPAAQ+FeOOH is almost twenty times higher than DMAPAAQ.

5 by DMAPAAQ. In the case of DMAPAAQ+FeOOH, besides Cl -, FeOOH also exchanges ion with Arsenic. That's why the Cl - released into solution is less than that of DMAPAAQ. Selectivity of Arsenic Adsorption Fig. 3 shows the effect of Sulphate concentration on the adsorption of arsenic. We found in the solution of Na2SO4 and Na2HAsO4.7H20, the selectivity of Arsenic adsorption of DMAPAAQ+FeOOH is almost twenty times higher than DMAPAAQ. Therefore, the selectivity of adsorption of Arsenic by DMAPAAQ+FeOOH is better than DMAPAAQ and DMAA+FeOOH. In the case of DMAPAAQ, arsenic is adsorbed to the gel by ionic interaction with the amino group. When the initial sulfate ion concentration is increased, the sulfate ion acts as an anion, which inhibits the adsorption of arsenic, causing the amount of arsenic adsorption to be decreased. Fig. 4 Adsorption of Sulphate Meanwhile, in the case of DMAA+FeOOH and DMAPAAQ+FeOOH, the adsorption amount of arsenic was slightly reduced, because the iron hydroxide can selectively adsorb arsenic by complex adsorption. With the increasing amount of Sulphate, the adsorption amount of arsenic by DMAPAAQ+FeOOH is higher than DMAA+FeOOH and DMAPAAQ. In order to elucidate the mechanism of the selective adsorption clearly, the adsorption amount of sulfate by DMAPAAQ and DMAPAAQ+FeOOH gel composite was measured (Fig. 4). The figure shows that the sulfate ions are mostly adsorbed by DMAPAAQ gel, but not by iron hydroxide. This phenomenon proves that Arsenic can be selectively adsorbed by DMAPAAQ+FeOOH gel composite. ph sensitivity of DMAPAAQ+FeOOH gel composite The ph sensitivity of DMAPAAQ+FeOOH gel composite is examined. The experiment was conducted with 2mmol/L of arsenic. Fig. 5 shows that, at low ph, the amount of adsorption is higher, but at high ph, the amount of adsorption is lower.

6 Amount of Arsenic Adsorption/Desorption [mmol/g-adsorbent] Amount of Adsorbed As [mmol/g] Regeneration of DMAPAAQ+FeOOH gel composite Fig. 6 shows the regeneration of DMAPAAQ+FeOOH gel composite. The adsorption of arsenic is performed in 2mmol/L Na2HAsO4.7H20 solution and the desorption of arsenic is performed in 0.5mol/L NaCl solution. As shown in the figure, the gel composite is successfully regenerated and Adsorption period: 24hr Temperature: 20 Volume of As: 40ml Concentration of As: 2mmol/L Gel weight: 20mg Equilibrium ph Fig. 5 ph sensitivity of DMAPAAQ+FeOOH gel composite the arsenic is desorbed by rinsing in NaCl solution repeatedly and the reusability of the gel will help to reduce the cost Sample 1 Sample 2 NaCl Concentration : 0.5M/L As Concentration : 0.2mM/L Temperature : 20 Stirrer Rotation : 120 rpm Solution Volume:40mL Gel Weight: 20mg Time [Day] Fig. 6 Reusability of DMAPAAQ+FeOOH gel composite.

7 CONCLUSION The selective adsorption of Arsenic by DMAPAAQ+FeOOH is better than DMAPAAQ and also, DMAPAAQ+FeOOH adsorbs better than the currently used methods. In real life, the concentration of Arsenic is lower than what we did in the lab experiment. Therefore, at low concentration of arsenic, the amount of arsenic adsorption by DMAPAAQ+FeOOH and DMAPAAQ may be close and better than iron hydroxide and non-ionic gels. Also, DMAPAAQ+FeOOH can be regenerated. Therefore, DMAPAAQ+FeOOH will help to adsorb Arsenic from water and provide good selectivity and reusability. Also, unlike the currently used methods, DMAPAAQ+FeOOH does not require any additional separation process. Hence, it ensures easy handling and simplify the process. REFERENCES 1. D. Mohan, et al. Journal of Hazardous Materials 142 (2007) R. Singh, et al. Ecotoxicology and Environmental Safety 112 (2015), Tomotaka Yanagita, arsenic adsorption properties of new iron hydroxide, Journal of water and environment 2013, 36(5),

CHAPTER 3. BATCH STUDIES FOR As(III) REMOVAL FROM WATER BY USING MAGNETITE NANOPARTICLES COATED SAND: ADSORPTION KINETICS AND ISOTHERMS

CHAPTER 3. BATCH STUDIES FOR As(III) REMOVAL FROM WATER BY USING MAGNETITE NANOPARTICLES COATED SAND: ADSORPTION KINETICS AND ISOTHERMS CHAPTER 3 BATCH STUDIES FOR As(III) REMOVAL FROM WATER BY USING MAGNETITE NANOPARTICLES COATED SAND: ADSORPTION KINETICS AND ISOTHERMS 41 42 3.1. INTRODUCTION Arsenic contamination of ground water and