Effects and mechanisms of oxalate on Cd(II) adsorbed on goethite at different pH and electrolyte concentration

The effects and mechanisms of oxalate on Cd(II) adsorbed by goethite at different oxalate concentration and pH in tested systems as well as the differences and reasons of the influence on Cd(II) adsorbed by goethite and by oxalated goethite were studied The results showed that oxalate in low concentration (1mmolL-1) promoted Cd sorption whereas oxalate in higher concentration (1mmolL-1) restrained Cd sorption There were some differences of the influence resulted from the oxalate which had been adsorbed by the goethite and the oxalate in the liquid phase It was mainly in relation to those, such as 1) the change of the surface charge characters was resulted from the oxalate sorption on goethite, 2) the oxalate distribution between solid phase and liquid phase, 3) the complexation and competition between oxalate and Cd 2+ The influence of electrolyte (KNO3) on Cd2+ adsorbed by goethite(G) and by oxalated goethite (G+40) was different obviously The Cd2+ sorption rates of goethite increased from 44.5% to 95% over with the increase of the electrolyte concentration whereas the Cd2+ sorption rate of oxalated goethite(G+40) decreased from 29% to 6.2% These were primarily dependent on the differences of their PZC and pH in tested systems