A Quantitative Modeling of Co-precipitation Phenomena in Wastewater Containing Dilute Anions with Ferrihydrite using a Surface Complexation Model

Abstract

Although numerous qualitative studies have been published on removal characteristics from wastewater of dilute anions by co-precipitation treatment with Fe(III) or Al salts, detailed mechanisms or quantitative characteristics are not well understood. In this study, a quantitative modeling of co-precipitation phenomena in wastewater containing dilute As(V), Se(VI), Cr(VI) or F with ferrihydrite was tried using a diffuse layer model (DLM), which is one of the most popular and simplest of surface complexation models. Co-precipitation experimental results from wastewater containing 2 mg/dm³ of Se(VI), 2 mg/dm³ of Cr(VI), or 15 mg/dm³ of F with ferrihydrite could be predicted quantitatively by the DLM with a existing set of parameters. However, results from wastewater containing 10 mg/dm³ of As(V) with ferrihydrite could not be predicted quantitatively but only qualitatively by the model. It was confirmed from the comparison of co-precipitation experimental results and simple adsorption ones that this quantitative difference between experimental and calculation data resulted from the procedure difference between co-precipitation and simple adsorption; in short, the precipitation of ferrihydrite and adsorption of As(V) develop simultaneously in the former system, and only As(V) adsorbs onto prepared ferrihydrite in the latter system.