Quantitative Modeling of As(V) Wastewater Treatment by Ferrihydrite Coprecipitation Using Surface Complaxaion and Surface Precipitation Model

Abstract

Construction and calculation using surface precipitation model were attempted for As(V) coprecipitaiton treatment with ferrihydride. Surface precipitation model was defined as extended surface complexation model. Original surface complexation model with parameter values reported by Dzombak and Morel was validated to adsorption experimental results for As(V) removal using ferrihydrite. The surface complexation model could represent experimental As(V) removal and isotherm quantitatively. In surface precipitation model, precipitation was described by the formation of solid compound between ferric hydroxide and ferric arsenate. Activity of these precipitates was determined by surface precipitation ratio of FeAsO4(s) obtained experimentally from XANES analyses. Solubility products of surface precipitation of FeAsO4(s) (KspAsO4(suf. ) were determined by fitting to sorption densities and surface precipitation ratio in each condition. The values of KspAsO4(suf.) were determined 10−7.7 at pH5 and 10−10.2 at pH7, respectively. These values were reasonably relative to the literatures and previous studies. Based on the obtained KspAsO4(suf.) value, As(V) removal and isotherm were calculated for As(V) coprecipitation treatment using surface precipitation model. Good agreement between experimental and calculated values was observed. For both of observed and calculated data, the sorption isotherms in coprecipitation treatment indicated saturated shapes because the species of surface precipitation was FeAsO4(s) and surface precipitation rate largely increased when As/Fe molar ratio is relatively low. These results were suggested that the quantitative prediction of As(V) coprecipitation treatment was possible if KspAsO4(suf.) value was estimated experimentally.