The electroreduction of molecular oxygen is investigated between -0.1 and -
0.5 V vs SHE on bornite, Cu5FeS4, at pH 9.2 and 14, by means of cyclic volt
ammetry (CV) and stationary voltammetry (SV), using a double channel electr
ode 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 -0.5
V then oxidized to CuS and Fe(OH)(3) above -0.1 V 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 pH 9.2 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, k(1) (direct way) and
k(2) (indirect way) of the oxygen electroreduction reaction. In contrast,
at pH 14, as soluble polysulphides are formed, it was possible to determine
these parameters, showing that the bornite is a poor catalyst for oxygen r
eduction. At pH 14, in the presence of potassium ethylxanthate, generally u
sed as a flotation collector, the ethylxanthate ions, C2H5OCSSO-, are oxidi
zed by HO2- to perxanthates, ROCSSO-, while at pH 9.2 the oxygen reduction
is inhibited due to ethylxanthate chemisoption on the bornite surface.