EXPERIMENTAL-STUDY OF CADMIUM-CITRATE COADSORPTION ONTO ALPHA-AL2O3

An experimental investigation of metal-organic co-adsorption was condu cted using cadmium and citrate in the presence of corundum. The experi ments were performed in the pH range 3.0 to 10.0 in a 0.01 M NaCl matr ix with citrate:Cd ratios of 0.00 and 10.00. The presence of citrate e nhances cadmium adsorption between pH 3.5 and 7.2, and reduces it abov e pH 7.2. The results from the experiments provide constraints on the thermodynamic properties of the surface complexes. We model the adsorp tion of Cd by quantifying the competition between aqueous CdCit(-1) an d the surface species, >AlCitCd(0), >AlOCd+, and >AlOCdCl0. The experi mentally determined equilibrium constants provide a means to predict C d mobilities in groundwater systems by describing the relative stabili ties of surface and aqueous metal-organic complexes as a function of m etal-to-ligand and solute-to-sorbent ratios.