Competitive Adsorption of As(III), As(V), and PO 4 by an Iron Oxide Impregnated Activated Carbon: Surface Complex Modeli
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Competitive Adsorption of As(III), As(V), and PO4 by an Iron Oxide Impregnated Activated Carbon: Surface Complex Modeling T. Angele Ngantcha-Kwimi & Brian E. Reed
Received: 30 June 2020 / Accepted: 27 August 2020 # The Author(s) 2020
Abstract The objective of this study was to predict the competitive adsorption of As(III), As(V), and PO4 by an iron oxide impregnated carbon (L-Act, 9% Fe(III) amorphous iron oxide) over a range of environmental conditions using the surface complexation modeling (SCM) approach. L-Act surface complexation constants determined from a single pH-adsorption edge were used to predict pH-dependent competitive removal in singular, binary, and tertiary adsorbate systems. As(III), As(V), and PO 4 complexes were modeled as bidentate binuclear species at low pH and monodentate species at high pH using the two monoprotic surface site/diffuse electric double layer model (2MDLM). F values determined based on 2MDLM predictions were close to those calculated by FITEQL (a statistical optimization program) demonstrating the effectiveness of the 2MDLM in describing adsorption behavior. F values were generally in the recommended range of 0.1–20 indicating a good fit between the data and the model. The 2MDLM also successfully predicted As(III)/As(V)/
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11270-020-04853-y) contains supplementary material, which is available to authorized users. T. A. Ngantcha-Kwimi Consolidated Edison of New York, 5th Floor NW, 4 Irving Pl, New York, NY 10003, USA T. A. Ngantcha-Kwimi (*) : B. E. Reed University of Maryland, Baltimore County, TRC Bldg, Rm 255A, Baltimore, MD 21250, USA e-mail: [email protected]
PO4 adsorption data of hydrous ferric oxide and goethite adsorbents from the literature. Keywords Surface complexation modeling . Competitive adsorption . As(III) . As(V) . PO4 . Iron impregnated activated carbon
1 Introduction Arsenic is of a serious environmental concern due to its toxicity and carcinogenicity (Chen et al. 1994; Smith et al. 1992). Consequently, the US EPA has reduced the maximum contaminant level (MCL) of arsenic in drinking water from 50 to 10 μg/L with a goal of 0 μg/L (US EPA 2001). As(V) is predominant under oxidizing conditions and is generally better adsorbed than As(III), while As(III) occurs predominantly under reducing conditions, is more mobile in ground waters, and is 60 times more toxic than As(V) (Jain and Ali 2000). While the MCL is based on total arsenic, the difference in toxicity and chemical behavior requires that attention be paid to the fate of individual arsenic species in treatment systems. The ability of iron oxides/hydroxides to remove As is well known (Dzombak and Morel 1990; Dixit and Hering 2003), but their use in fixed-bed columns is a challenging due to their small particle size, low hydraulic conductivity, and durability; thus, they have been impregnated onto more durable materials such as activated carbons, sand, and diatomite (Vaishya and Gupta 2003; Jang et al. 2006
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