Arsenic Removal from Wastewater by Modified Adsorbents

Arsenic Removal from Wastewater by Modified Adsorbents

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Procedia Engineering

ProcediaProcedia Engineering 00 (2011) 000–000 Engineering 18 (2011) 285 – 288 www.elsevier.com/locate/procedia

The Second SREE Conference on Chemical Engineering

Arsenic Removal from Wastewater by Modified Adsorbents Huang Jianhonga, Nie Fenga,b, Peng Fuquana*, Guo Qingweia, b

a South China Institute of Environmental Sciences,MEP,Guangzhou,510655,China School of Urban Construction, University of South China, Hengyang, Hunan,421001,China

Abstract A new adsorbent of arsenic was synthesized to treat arsenic bearing contaminated water. Strong anion resins 201×7 and D301 resins were chosen as carriers to synthesized hydrated ferrous oxide loaded on polymeric substrate. Results showed that 201×7 and D301 had exchange capacities of 1.20 mg/g and 0.78 mg/g on arsenic, respectively; modified adsorbents by 201×7(designated as PDR-HFO) had better sorption properties than that by D301 and sorption capacities were more than 3 times of 201×7 exchanger; PDR-HFO can decrease As concentration to less than 0.01 mg/L reaching national standards for arsenic and it exhibited excellent adsorptive properties and recyclability.

© 2010 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Resources, Environment and Engineering Keywords:adsorbent ; 201×7 ; hydrated ferrous oxid; HFO-PDR; sorption; recyclability

1. Introduction Arsenic exists with other ions extensively in natural waters. Currently, people are paying increasing concerns on arsenic toxicity and its contaminations. Most developed countries revised the MCL for arsenic at 0.01 mg/L (10 µg/L). China also set a new arsenic guideline of 10 μg/L(GB 5749-2006), which was enforced on July 1, 2007 [1]. Inorganic arsenicals are proven carcinogens in humans and toxic to both plants and animals [2]. Arsenic usually exists in many minerals. Arsenic pollution was aroused by geological chemical reactions and human activities[3,4]. Different adsorbents were used to remove arsenic from wastewater. In this study, extensive experiments of different adsorbents were conducted to elucidate their advantages and disadvantages compared with new PDR-HFO. Which was based on hydrated ferrous oxide loaded on polymeric substrate. * Corresponding author. Tel.: +086-13668711785 E-mail address: [email protected]

1877-7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.11.044

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2. Materials and methods 2.1. Materials Strong anion resin 201×7 and D301, modified adsorbents, presented as PDR-HFO. Grade of reagents used is analytical and they were dissolved in deionized water for further tests. Arsenic wastewater was sampled from storage tank of a chemical industry. Fluctuations of arsenic concentration owe to rainfall and some other reasons. 2.2. Batch and Column Breakthrough Adsorption Experiments Add adsorbents into conical asks containing wastewater stirring at 250 round per minute for 1 hour and test concentration of arsenic after centrifugation. Column experiments were performed with anion exchange column of 1.5 centimetres diameter and 30 centimetres length. Influent flow velocity was maintained by a peristaltic pump. Put 15 grams adsorbents(1 bed volume, BV, about 27 ml) into the column. All the samples were taken under same conditions. After adsorption, desorption of breakthrough adsorbent was performed by 10% HCl (v/v) and regenerated by saturated FeCl 3 . Adsorption compounds can be monodentate complex and bidentate complex under electrostatic and Lewis bases functions. 2.3. Analyses Total arsenic was analyzed according to siliver diethyldithiocarbamate spectrophotometric method [5] and arsenate was tested by atomic fluorescence spectropho-tometer(ASF-230a). It was provided by Analytic Centre of South China Institute of Environmental Sciences, MEP. Fe(III) was analyzed according to phenanthroline spectrophotometry[6]. 3. Results and Discussions 3.1. Arsenic Removal of 201×7 and D301 Two different kinds of concentration wastewater were chosen as the arsenic bearing reagents. Arsenic concentration for 201×7 and D301 were 14.09 and 10.25 mg/L respectively. Breakthrough experiments results were showed in Fig. 1.

Fig. 1. Breakthrough Curve of 201×7 and D301 resins Data above showed that both 201×7 and D301 resins can decrease the concentration of As to less than 10ppb reaching GB 5749-2006; after 40 and 120min concentrations of As of effluent by 201×7 exceed 10ppb and 50ppb while the time of D301 is 30 and 100min respectively, TAs of both of 201×7

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and D301 resins is more than 100ppb after 190min; 201×7 has higher exchange capacity than that of D301 and lower TAs of effluent at the same time under condition that TAs of influent of 201×7 is 14.09 ppm while that of D301 is 10.25ppm. At 420min and 350min 201×7 and D301 resins reach exchange equilibrium with exchange capacity of 1.20mg/g and 0.78 mg/g , respectively. As a result of effects of some other ions such as SO 4 2-、Cl-、 CO 3 2- 、NO 3 - on exchange process, the actual exchange capacity is lower than theoretical exchange capacity. 3.2. Effects of pH on 201×7 and D301 Resins’ Removal of Arsenic Different pH affected sorption on arsenic because of ions strength and it was drawn in Fig. 2.

Fig. 2. Removal of As by 201×7 and D301 Resins under different pH The optimum pH of 201×7 and D301 resins varies from 5 to 8; existence of some metal ions such as Pb2+,Cr3+,Zn2+,etc. can generate hydroxide when pH=10 causing that TAs is lower than pH=9 but still higher than pH=5-8. 3.3. Column Adsorption Experiment Hydrated ferrous oxide(HFO) has arose our focus on arsenic removal in recent years. Hydrated ferrous oxide(HFO) loaded on polystyrene diethanolamine resin was used to treat arsenic-contaminated wastewater shown in Figure 6. The breakthrough point was set as 10 µg/L, as indicated by standards for drinking water quality (GB 5749-2006)for arsenate set by Ministry of Health of the People’s Republic of China, PRC. Effluent after 195 BVs, concentration of arsenic exceeded 0.01 mg/L; after 415 BVs arsenic concentration of effluent exceeded that of influent. After regeneration, breakthrough volumes were 165 BVs and 398 BVs respectivelt, regeneration rate was more than 96%. Detailed properties of regeneration were shown in Figure 7.

Fig. 3. Breakthrough curve of PDR-HFO

Fig. 4. Recyclability of adsorbents

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PDR-HFO had excellent recycling properties. Through comparison with strong anion resin, concentration of arsenic in effluent by strong anion resin was hard to meet standards for arsenic (GB 5749-2006) and adsorption capacity reduced sharply after regeneration. 4. Concluding remarks 201×7 and D301 resins can decrease As concentration to less than 0.01mg/L and the former was better. Polymeric anion exchanger is an excellent substrate because it allows enhanced permeation of anions within the polymer phase due to its high concentrations of fixed positive charges[7]. Polymer or zeolite supported metal oxide/metal particles are finding wider applications in catalysis, bioseparation, drug delivery, and environmental remediation [8]. It has a lower adsorption capacity compared with HFO-PDR and some anions such as SO 4 2- can not be removed when it is regenerated causing its sharp loss of adsorption capacity. Therefore, HFO-PDR is a good adsorbent of arsenic for groundwater. However, it still needs to be modified to improve its selective capacity and sorption capacity. Acknowledgements Partial financial supports from South China Institute of Environmental Sciences are gratefully acknowledged. This paper was reviewed by Dr. GUO Qing-wei, Dr. HUANG Jian-hong. Their suggestions and comments were of valuable assistance in preparing the final document. References [1] An Overview of ArsenicTreatment Methods, Dennis Clifford University of Houston,Houston,10,21,2003 [2] Jorge Christian Navarro Aragon, Dringking Water Quarlity in Northern Mexico and Arsenic Treatment with Iron Impregnated GAC, Arizona State University,12,2005. [3] Bissen M, Frimmel FH. Arsenic-a review. Part I: occurrence, toxicity, speciation, and mobility. Acta Hydrochim Hydrobiol. 2003a, 31, 9–18. [4] Bissen M, Frimmel FH. Arsenic-a review. Part II: oxidation of arsenic and its removal in water treatment. Acta Hydrochim Hydrobiol. 2003b, 31, 97–107. [5] Water quality-Determination of total arsenic-siliver diethyldithiocarbamate spectrophotometric method. GB 7485-87. [6] Water and Wastewater Monitoring Analysis Method, fourth edition, State Environmental Protection Administration 2002. [7] Design Manual:Removal of Arsenic from Drinking Water by Ion Exchange, Frederick Rubel, Jr.Rubel Engineering, Inc.Tucson, Arizona,6,2003. [8] Mayer, D.; Wood, K.; Bachas, L. G.; Bhattacharyya, D. Degradation of chlorinated organics by membrane- immobilized nano-sized metals. Environ. Prog. 2004, 23 (3), 232-242.