Surface modification of goethite by phosphate for enhancement of Cu and Cd adsorption

In order to understand the role of phosphate in the reactions of heavy metals on mineral surfaces, phosphate was used to modify goethite and then adsorption of copper and cadmium on the pristine and phosphate-modified goethite was investigated. Compared with the pristine goethite, the phosphate-modified goethite had a higher adsorption capacity and a faster adsorption rate. Surface characteristics, such as specific surface area, pore size distribution, zeta potential and surface charges, were then systematically investigated in order to examine the relevant mechanism for the enhancement of copper and cadmium adsorption onto the phosphate-modified goethite. It was found that the decreased surface charge contributed most to the higher adsorption capacity and the enlarged average pore size was mainly responsible for the fast adsorption kinetics, while there was no direct link between specific surface area and the adsorption capacity.