THE EFFECT OF COMPLEXING AGENTS

The photo-oxidative dissolution of cadmium sulfide has been investigat ed in the presence of several complexing organic and inorganic compoun ds under oxygen-saturated conditions. At pH 4 and 7, aromatic organic ligands enhance the cadmium dissolution rate by a factor of 5-6 over t hat without the organic present; EDTA, NTA, and citric and oxalic acid s have little effect. Sulfite and hydrogen sulfide/bisulfide slightly enhance the dissolution. Conversely, at pH 10, EDTA and NTA produce a significant increase in dissolved cadmium (factor of approximately 18) while the other compounds exert little effect. These phenomena are ex plained by ligand surface complexation, and both surface and homogeneo us ligand-cnhanced dissolution.