ELECTROCHEMICAL STUDY OF SURFACE OXIDATION AND COLLECTORLESS FLOTATION OF ARSENOPYRITE

The surface oxidation of arsenopyrite in alkaline solutions has been studied by cyclic voltammetry. The initial oxidation of arsenopyrite surface produces ferric hydroxide and a realgar-like compound according to the following rection: FeAsS + 3H2O double-line arrow pointing left and right Fe(OH)3 + AsS + 3H+ + 3e-At higher potentials, the oxidation of arsenopyrite results in elemental sulphur and arsenate according to the following overall reaction: FeAsS + 7H2O --> Fe(OH)3 + HASO42- + S0 + 10H+ + 8e-Ferric hydroxide is precipitated and arsenate stays on the surface. Both elemental sulphur and realgar (AsS) are retained on the arsenopyrite substrate. Oxidation of arsenopyrite surfaces is not affected by potential cycling or by the presence of arsenic or sulphide species. The oxidation of hydroxyl ions takes place simultaneously with the arsenopyrite oxidation. Flotation tests demonstrated that freshly ground arsenopyrite is non-floatable in the absence of xanthate as collector. Good flotation was obtained for both freshly ground and aged arsenopyrite in the presence of EDTA. The flotation results support the reactions for arsenopyrite oxidation drawn from the electrochemical studies.