Sergio Castro

Environmental viewpoint on small-scale copper, gold and silver mining in Chile

Abstract This paper analyses the importance and environmental impacts of metallic small-scale mining in Chile. This sector is characterized by the exploitation of primarily artisanal copper (Cu), gold (Au), and silver (Ag) deposits, which are dispersed throughout (Chilean) Regions I through VI, with heaviest concentrations in Regions III and IV. In 2000, Chilean small-scale mines employed some 1700 workers (5.1% of total mining workers), and plants with a production capacity of less than 50 tpd accounted for 0.97% (44,603 t) of Cu; 6.5% (3,484) of Au; and 1.1% (13,665 kg) of Ag output in the country. High-grade ore extraction, flotation, gravity concentration, acid leaching–cementation, and mercury amalgamation, are the main metallurgical technologies employed. Following an overview of Chilean small-scale mining, the paper examines the environmental impacts of its production processes, and discusses the legal support and regulatory framework in place for operations.

The stabilizing effect of Na2S on the collector coating of chrysocolla

Abstract The heterogeneous reaction between natural and sulphidized chrysocolla and potassium amyl xanthate in solution is investigated. It is found that, together with the consumption of large amounts of xanthate, particles composed of the reaction products are spontaneously released from the surface of chrysocolla giving rise to a colloidal dispersion. In principle the mechamism is related to the peptizing effect of the excess xanthate ions that are found when Cu 2+ and X − ions are made to react in a homogeneous phase. In sulphidized chrysocolla this phenomenon is markedly reduced, showing that Na 2 S has a stabilizing effect on the collector coating. Flotation experiments performed with aqueous amyl dixanthogen emulsions show that stable adhesion occurs only on properly sulphidized chrysocolla. It is believed that the mechanism controlling adhesion in this case is similar to that which determines the stability of the collector layer.