INTERACTIONS BETWEEN SULFIDE MINERALS AND ALKYLXANTHATES .7. A VIBRATION AND X-RAY PHOTOELECTRON SPECTROSCOPIC STUDY OF THE INTERACTION BETWEEN COVELLITE AND ALKYLXANTHATE IONS AND THE NON-SULFIDE MINERAL MALACHITE AND ETHYLXANTHATE IONS IN AQUEOUS-SOLUTION

The reactions between covellite, CuS, and malachite, Cu2CO3(OH)2, and aqueous and acetone solutions of potassium ethylxanthate and decylxanthate have been studied. X-ray photoelectron spectroscopy (XPS) has been used to determine the oxidation state of copper in the surfaces of the minerals. The XPS measurements showed that copper is present as copper(I) and copper(II) on the surfaces of covellite and malachite respectively. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy has been used for qualitative analysis of the alkylxanthate species present on the mineral surfaces after treatment with an aqueous solution of potassium alkylxanthate. Solid copper(I) alkylxanthate is the predominating alkyxanthate species formed on covellite. Very small amounts of dialkyl dixanthogen are found on the covellite surfaces as well. Solid copper(I) alkylxanthate is sorbed on the covellite surfaces according to a dissolution-precipitation mechanism in which copper(I) species are dissolved from the covellite surface, a concentration gradient of copper(I) species is formed around the covellite particles and copper(I) alkylxanthate is precipitated back on the covellite surface in the presence of a suitable concentration of alkylxanthate ions. No experimental evidence for the formation of chemisorbed complexes of alkylxanthate ions on covellite surfaces was found. Solid copper(I) alkylxanthate and dialkyl dixanthogen are both present in large quantities on malachite surfaces after treatment with an aqueous solution of potassium alkylxanthate, as expected for a copper(II) mineral.