Abstract
The electroreduction of molecular oxygen is investigated between −0.1 and −0.5V vs SHE on bornite, Cu5FeS4, at pH9.2 and 14, by means of cyclic voltammetry (CV) and stationary voltammetry (SV), using a double channel electrode flow cell (DCEFC). Using an E/pH diagram established in this work, the CV results suggest that the bornite surface is stable between −0.1 and −0.5V then oxidized to CuS and Fe(OH)3 above −0.1V whereas, below −0.5V the mineral reduces to metal sulphides: Cu2S and FeS. The SV results show that oxygen is reduced to peroxide ions, HO2−. At pH9.2 the generated sulphide ions hinder the oxidation of HO2− on the collector electrode of the DCEFC, due to the formation of a blocking surface layer of elemental sulphur, S, impeding the determination of the kinetic parameters, k1 (direct way) and k 2 (indirect way) of the oxygen electroreduction reaction. In contrast, at pH14, as soluble polysulphides are formed, it was possible to determine these parameters, showing that the bornite is a poor catalyst for oxygen reduction. At pH14, in the presence of potassium ethylxanthate, generally used as a flotation collector, the ethylxanthate ions, C2H5OCSSO−, are oxidized by HO2− to perxanthates, ROCSSO−, while at pH9.2 the oxygen reduction is inhibited due to ethylxanthate chemisoption on the bornite surface.
Published Version
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