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Studies on the depressive action of chromate and dichromate salts on galena Okada, Susumu

Abstract

In the course of the experimental work conducted it was found that when galena was treated with chromate salts or dichromate salts in an aqueous solution, lead chromate identified by infrared spectroscopy was the main species adsorbed on the galena surface. The formation of chromium hydroxide or chromium oxide was not observed. Thermodynamic considerations of the Pb-Cr-S-H₂0 bulk system indicate the very stable character of lead chromate as shown in the potential-pH diagram constructed in this study. It is also seen that no stable domain of lead dichromate exists. The adsorption rate as well as adsorption amount of dichromate at the pseudo-equilibrium condition increases with the decrease in pH value. This phenomenon supports the fact experienced in galena flotation that a dichromate salt is a much more efficient depressant than is an equivalent chromate salt. The desorption of xanthate from galena surfaces covered with more than a monolayer thickness of xanthate was found to be possible by adding chromate salt to the system, whereas chromate desorption from galena surfaces due to xanthate addition was not observed. It was found that under comparable conditions xanthate adsorbed on lead chromate surfaces oxidized to dixanthogen much more readily than xanthate adsorbed on galena surfaces.

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