A study of the surface oxidation of arsenopyrite using cyclic voltammetry

Abstract

Electrochemical methods and surface spectroscopy have been used to study the surface oxidation of arsenopyrite. Cyclic voltammetric studies indicated that the oxidation of arsenopyrite at pH greater than 7 results in the formation of ferric hydroxide deposits on the surface of the mineral. Arsenic is oxidized to arsenate and sulphur is oxidized to sulphate. The arsenate is incorporated in the ferric hydroxide deposits while sulphate diffuses into solution. Below pH 7, soluble iron species are formed and the surface becomes increasingly covered with elemental sulphur with decreasing pH. Increasing temperature has no influence on the quantity of hydroxide formed over the range 30–45°C but results in thick, porous films at temperatures greater than 45°C. The oxidation of arsenopyrite was demonstrated to occur at lower oxidation potentials than for pyrite although this effect decreased with increasing temperature. Mixed potential studies indicated that the potentials required for arsenopyrite oxidation could be achieved with common oxidizing agents. The selective oxidation of arsenopyrite in a bulk pyrite/arsenopyrite concentrate was indicated to be possible. The formation of iron hydroxide deposits on the surface of arsenopyrite resulted in the inhibition of subsequent oxidation of xanthate to dixanthogen at the mineral's surface. ESCA studies confirmed the formation of oxidized iron layers at the surface of arsenopyrite and revealed that essentially all the arsenate which was formed was incorporated in these layers. Sulphur became oxidized at the pH studied and to a large extent went into solution.