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 PO4 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)/PO4 adsorption data of hydrous ferric oxide and goethite adsorbents from the literature.
Highlights
Arsenic is of a serious environmental concern due to its toxicity and carcinogenicity (Chen et al 1994; Smith et al 1992)
While the maximum contaminant level (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; they have been impregnated onto more durable materials such as activated carbons, sand, and diatomite
Summary
Arsenic is of a serious environmental concern due to its toxicity and carcinogenicity (Chen et al 1994; Smith et al 1992). 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). Iron oxide impregnated activated carbon, the study adsorbent in our work, is durable, could potentially allow the concurrent removal of organics and inorganics, and enjoys widespread familiarity with drinking water professionals (Reed et al 2000; Vaughan and Reed 2005; Ngantcha et al 2011). Iron oxide impregnated activated carbons are ideal for use by small communities and in point-ofuse devices to treat arsenic contaminated water
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