Surface complexation modeling was examined in this study for prediction of arsenate, natural organic matter, and silica removal by ferric hydroxides. Estimation of surface potential and the predicted effect of hardness, natural organic matter, silica, and sulfate on arsenate removal were also addressed. The model accurately predicted arsenate removal from synthetic and natural water by adsorption and coagulation under a range of circumstances. Accurate modeling of arsenic removal in the presence of silica required explicit consideration of both monomeric and dimeric silica species. Natural organic matter and silica are predicted to significantly reduce arsenate removal by competition, development of anionic surface charge, and by hindered flocculation when surface potential is unfavorable. Accurate surface complexation models could be a powerful tool in modeling coagulation performance for a number of contaminants. Includes 20 references, tables, figures, appendix.