Effect of magnetite particle size on adsorption and desorption of arsenite and arsenate
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C.T. Yavuz, J.T. Mayo, and W.W. Yu Department of Chemistry, Rice University, Houston, Texas 77005
A.T. Kana) Department of Civil and Environmental Engineering, Rice University, Houston, Texas 77005
V.L. Colvin Department of Chemistry, Rice University, Houston, Texas 77005
M.B. Tomson Department of Civil and Environmental Engineering, Rice University, Houston, Texas 77005 (Received 25 April 2005; accepted 2 August 2005)
Numerous studies have examined arsenic adsorption on varying adsorbents including iron oxides, aluminum hydroxides, alumina, and carbon as a means of arsenic removal in drinking water treatments. The objectives of this study were to evaluate the effect of magnetite particle size on the adsorption and desorption behavior of arsenite and arsenate, and to investigate the competitive adsorption between natural organic matter (NOM) and arsenic. Increases in adsorption maximum capacities for arsenite and arsenate were observed with decreasing magnetite particle size. Arsenic desorption is hysteretic, more so with the smaller nanoparticles. Such desorption hysteresis might result from a higher arsenic affinity for magnetite nanoparticles. In the presence of NOM, substantial decrease in arsenic sorption to magnetite nanoparticles was observed. It would be beneficial to thoroughly investigate adsorption and desorption of arsenic on magnetite nanoparticles for further practical purposes. I. INTRODUCTION
Arsenic-contaminated groundwater, used as drinking water, has been a severe problem in Bangladesh but is also common in United States.1 Several studies have reported the health hazard due to the chronic exposure to arsenic.2,3 To address the problem, the World Health Organization (WHO) guideline value and the European maximum permissible concentration (MPC) for arsenic in drinking water are set as 10 g/l. The United States Environmental Protection Agency4 also lowered the drinking water standard for arsenic from 50 to 10 g/l starting January 2006. A variety of arsenic-removal technologies are currently available including coprecipitation, adsorption in fixed-bed filters, membrane filtration, anion exchange, electrocoagulation, and reverse osmosis.5,6 The focus of research has now shifted to solve the problem using suitable sorbents to achieve a low arsenic level in drinking water for communities with a high raw water arsenic concentration.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0403 J. Mater. Res., Vol. 20, No. 12, Dec 2005
Numerous papers have been published, which demonstrate that iron oxides have a high affinity for the adsorption of arsenite and arsenate.7,8 Although iron oxides have different structures, arsenic adsorption is not affected by their structures.9 The surface properties of iron oxides are key factors in adsorption on iron oxides. However, the sorption behavior of arsenic is strongly influenced by solution pH and the oxidation state of arsenic. Arsenate is more strongly retained at low pH values,8 whereas there is conflict about arseni
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