Interactions between sulphide minerals and alkylxanthates 8. A vibration and X-ray photoelectron spectroscopic study of the interaction between chalcopyrite, marcasite, pentlandite, pyrrhotite and troilite, and ethylxanthate and decylxanthate ions in aqueous solution

Abstract

The reactions between chalcopyrite, CuFeS 2, marcasite, FeS 2, pentlandite, (Fe,Ni) 9S 8, pyrrhotite, FeS 1- x , and troilite, FeS, and aqueous solutions of potassium ethylxanthate and decylxanthate have been studied. X-ray photoelectron spectroscopy (XPS) has been used to determine the oxidation state of copper at the chalcopyrite surface. The XPS measurements showed that copper at the surfaces of chalcopyrite is present as copper(I) Qualitative analysis of the alkylxanthate species present on the mineral surfaces after treatment with an aqueous solution of potassium alkylxanthate has been made by means of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Solid copper(I) alkylxanthate is the only alkylxanthate species found on the chalcopyrite surfaces. Alkylxanthate ions are sorbed to chalcopyrite surfaces according to a dissolution—precipitation mechanism where copper(I) species are dissolved from the chalcopyrite surfaces, a concentration gradient of copper(I) species is formed around the chalcopyrite particles, and copper(I) alkylxanthate precipitates back on the chalcopyrite surface in the presence of small concentrations of alkylxanthate ions. Large amounts of dialkyl dixanthogen formed in a redox reaction between alkylxanthate ions and highly oxidising species on the marcasite surfaces are present on the marcasite surfaces after treatment with an aqueous solution of alkylxanthate. This oxidising agent is most probably a minor oxidation product of the disulphide ions in marcasite, e.g. S 2O 2− 8 and/or S 2O 2− 7 ions, which are probably formed during grinding in air. Dialkyl dixanthogen is the only alkylxanthate species found on the surfaces of pentlandite and pyrrhotite, but the amounts are substantially smaller than on marcasite. The sulphur in pentlandite and pyrrhotite is most probably mainly oxidised to sulphate ions, but very small amounts of a strong oxidising agent seem to be formed as well. No alkylxanthate species have been found on the surfaces of troilite after treatment with alkylxanthate ions. The relationship between the kind of alkylxanthate species formed on the sulphide mineral after treatment with an aqueous alkali alkylxanthate solution and the structure of the mineral is discussed.