Arsenic removal by a colloidal iron oxide coated sand

Abstract

A novel treatment process for arsenic removal from contaminated groundwater has been developed for use as a reactive barrier or a small drinking water treatment unit. In this study, modified porous media was made by the deposition of colloidal iron oxide onto sand grains at intermediate pH and ionic strength. K-d values from column experiments were 0.016-0.37 L/kg for As(III) and 0.023-0.85 L/kg for As(V), being lower than those of batch experiments (0.50 and 1.30 L/kg for As(III) and As(V), respectively) due to lower availability of surface adsorption sites in the packed column. Media-independent K,1 values reflect the enhancement of arsenic adsorption with an increase of colloidal iron oxide coated sand fraction, apparently due to adsorption equilibration during arsenic transport under the same flow column conditions. The heterogeneous composition of two groundwater samples also reduced arsenic adsorption. Therefore, arsenic elution near the initial breakthrough was regulated by available adsorption surface in a porous coated sand media as well as the effects of competing oxyanions. The exhaustion of adsorption capacity near the critical contamination level is sensitive to geochemical and remedial properties of the contaminants.