The alkaline sulphide leaching of tetrahedrite concentrate

An inv estigation was made into the leaching of tetrahedrite concentrate . by strong sodium sulphide/sodium hydroxide solutions. The experiments were designed to avoid oxidation of the elements present and so,solubilize antimony as antimony (III) - sulphide complexes. Analytical techniques were developed for the analysis of caustic and sulphur species (S²⁻ , S⁰[sub x-1], S₂O₃ ²⁻and SO₃²⁻ ) in antimony-containing solutions. The quantity of antimony extracted from the tetrahedrite was found to be a function of both the sulphide and hydroxide concentrations. Sodium thioferrate, a reaction product of pyrite and sodium sulphide, was indicated as a leaching agent. The solid concentrate decomposition product was x-ray amorphous and colloidal. Though a positive identification of this material was not possible it was found that one iron and one sulphur were added to the product for each antimony extracted from the tetrahedrite. An analysis of literature stibnite solubility data was done and showed that below log [Sb] (M) = -0.7 . Sb₂S₄²⁻ is probably the predominant antimony (III) - sulphide complex in saturated soltuion at 25°C. Above log [Sb] (M) = -0.7 , Sb₄S₇²⁻ is the most likely predominant complex. The results of the leaching study are not directly applicable to commercial tetrahedrite leach processes where the solutions contain oxidized sulphur species, in particular polysulphide. Antimony leached in these processes exists as antimony (V) - sulphide complexes.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat