Mechanisms of pyrite flotation with xanthates

Abstract

Thermodynamic equilibrium calculations have been carried out for the Fe-S-X-CO 3 2−-H 2O systems, where X denotes xanthates. The results were interpreted by means of dominance and distribution diagrams to study the stability of Fe(III)-xanthate compounds under different chemical conditions. Selected electrochemical studies on the pyrite/ethyl xanthate systems are compared with the results obtained by flotation and infrared spectroscopic techniques, and are correlated with the thermodynamic studies to elucidate the mechanisms involved in the flotation of pyrite with xanthates as collectors. Contrary to previous studies, our studies show that dixanthogen is not the sole species responsible for the flotation behavior of pyrite. The thermodynamic stability studies demonstrate that insoluble Fe(III)-xanthate compounds can be formed under normal flotation conditions. The results of pyrite flotation with ethyl xanthate indicate that the formation of ferric dihydroxy ethyl xanthate on pyrite surfaces can either improve or deteriorate the floatability of pyrite, depending on the concentration of ethyl xanthate. Good flotation can be obtained when ethyl xanthate ions and/or diethyl dixanthogen are coadsorbed on ferric dihydroxy ethyl xanthate sites. Electrochemical measurements in the pyrite/ethyl xanthate systems show that the open-circuit potentials of pyrite electrodes in ethyl xanthate solutions are essentially independent of the solution pHs, and furthermore, are within the stability regions of Fe(III)-ethyl xanthate compounds. This also indicates that the pyrite surfaces may be covered by Fe(III)-ethyl xanthate compounds. FTIR spectroscopic studies confirmed the formation of Fe(III)-xanthate compounds on the pyrite surfaces. The Fe(III)-xanthate compounds are strongly bonded to the pyrite surface. Above the Fe(III)-xanthate compound layer, dixanthogens and xanthate ions are co-adsorbed probably as multiple layers.