Individual and competitive adsorption of Cr(VI) and phosphate onto synthetic Fe–Al hydroxides

Individual and competitive adsorption characteristics of Cr(VI) and phosphate (P) onto synthetic Fe–Al hydroxides were investigated. A series of batch experiments were performed to study the influence of various experimental parameters (pH, ionic strength and contact time) on Cr(VI) and P adsorption. Removal efficiency of Cr(VI) and P decreased with increasing pH and ionic strength. In individual adsorption tests, pseudo-second-order kinetic and Langmuir isotherm models could better describe Cr(VI) and P adsorption on Fe–Al hydroxides. In competitive adsorption experiments, Cr(VI) adsorption was suppressed obviously by P and followed Freundlich isotherm model, revealing that the competitive adsorption of Cr(VI) in the presence of P was heterogeneous. Cr(VI) had no significant influence on P adsorption and the competitive adsorption of P agreed well with Langmuir isotherm model, suggesting that the competitive affinity of P towards the adsorption sites on Fe–Al hydroxides was stronger than that of Cr(VI). The presence of P reduced the adsorption amount of Cr(VI), but the presence of Cr(VI) decreased the adsorption rate of P.