Mechanochemical processing of chrysocolla with sodium sulphide

Autogenous solid state processing of chrysocolla with sodium sulphide has been carried out at different CuSiO₃–Na₂S-ratios, particle sizes and temperatures. Water soluble sodium silicate (Na₂SiO₃) and covellite (CuS) were determined by means of chemical analysis and X-ray examination as reaction products. More than 84% of chrysocolla and 50% of associated malachite were converted to covellite at 80 °C, atmospheric pressure, 10 min contact time, stochiometric CuSiO₃–Na₂S-ratio and particle sizes of <100 μm. The mechanochemical treatment using a vibrating mill increases the conversion rate of chrysocolla and malachite up to 90% and 70%, respectively. After washing of the products, the sodium silicate solution was converted into sodium sulphate (Na₂SO₄) by adding sulphuric acid, with precipitation of silica as by-product. In addition, the carbothermic reduction of crystallised sodium sulphate led to sodium sulphide necessary for solid state processing.