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Removal of Arsenic Using a Cationic Polymer Gel Impregnated with Iron Hydroxide
Published on: June 28, 2019
Experimental and geochemical modeling study of coexisting Arsenic(III) and Arsenic(V) removal by ferrihydrite
Hisanori Iwai1, Kaito Yamagata1, Y K Kong2
1Department of Resources and Environmental Engineering, Faculty of Science and Engineering, Waseda University, Tokyo, 169-8555, Japan.
Abstract:
Arsenic (As) adsorption onto ferrihydrite (Fh) is an effective method for reducing As concentrations and is commonly used in passive mine drainage treatment. A model that predicts the removal of As(III) and As(V) is essential for designing treatment conditions. In this study, the mechanism of As removal in an As(III)-As(V) coexisting system by Fh at pH 7 was clarified. The presence of As(V) inhibited the surface complexation of As(III) on Fh. X-ray absorption fine structure (XAFS) analysis showed that surface precipitation of FeAsO4 was suppressed at a low As/Fe ratio, while the proportion of surface-complexed As(III) increased. A geochemical model incorporating surface complexation and precipitation of As to Fh was developed using PHREEQC and reproduced experimental results by adjusting the solubility product (Ksp) of FeAsO4 according to the As/Fe ratio. This model also reproduces the arsenic removal behavior observed at sites where As removal by Fh generation is being attempted. Because this model is based on equilibrium reactions, to manage field treatment using model predictions, it is desirable to avoid conditions where Fh redissolution and reprecipitation occur, and to design a hydraulic residence time (HRT) of 10 h or more.
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