Predicting Arsenate Adsorption on Iron-Coated Sand Based on a Surface Complexation Model

Abstract

Equations were developed to predict arsenate sorption on iron oxide coated sand, on the basis of the constant capacitance surface complexation model, assuming formation of bidentate surface complexes between arsenate and iron oxyhydroxide surface sites. The developed equations can predict arsenate adsorption when initial arsenate concentration, adsorbent concentration, and solution pH are known. The average discrepancy between experimental data and modeling results was less than 5%. The maximum arsenate sorption capacity is the only parameter required that needs to be estimated from experimental data. The developed equations were validated by modeling arsenate adsorption on iron oxide sand over the pH range 5–8, under various initial arsenate concentrations and iron oxide coated sand solid concentrations. The developed predictive equation can also be used for calculating arsenate adsorption performance on iron impregnated activated carbon. Finally, the developed equation can be used to calculate sorption media dose requirements by specifying initial arsenate concentration, arsenate removal goal, and solution pH.