Some Recent Developments In The Extraction Metallurgy Of Gold In South Africa PDF Download

The South African gold industry is approximately one hundred years old, and is still characterized by a dynamic spirit of research and innovation. With the apparently inexorable rise in the price of gold, even minor improvements in recovery or reductions in operating costs have major economic significance. Recent advances in metallurgical research and development include the following: (i) An electrochemical explanation for the gold-cementation process. This indicates why such large amounts of zinc - some twenty times the stoichiometric requirement - together with lead nitrate are necessary for the almost complete precipitation of gold from cyanide solution. (ii) Application of the carbon-in-pulp process to the direct extraction of dissolved gold from cyanidation pulps. Novel features include a technique for retaining the loaded granules of activated carbon against the pulp flow, a new technique for subsequent stripping of the gold from the carbon, and the development of a packed-bed electrode cell for electrowinning of the gold from the eluate. A solution to the problem of clogging in the ball matrix of wet high-intensity magnetic separators used for the beneficiation of Witwatersrand uranium-and-gold-bearing residues. The balls, which are in a carousel, are removed continuously through a side discharge, are cleaned, and are returned to the separator. (iv) The development of a powerful but compact centrifugal mill for the underground milling of Witwatersrand ores in deep mines so that the milled product can be concentrated and then pumped to the surface, the discard material being used as backfill in the excavation. The anticipated reduction in the amount of energy required to hoist low-grade ores through thousands of metres, together with a reduction in ventilation and supporting structures, promises to extend the lives of mines that have become too deep to be exploited economically with existing technology. (v) The large-scale reclamation of gold from tailings dumps. One example involves the retreatment of several mine dumps many kilometres apart at a central processing plant - the Ergo project. Apart from a plant handling 2100 tons of dump material per hour, housing 156 flotation cells (the majority of which are 14 000 litres in volume) and three tailings-thickener tanks each 138 metres in diameter, the production and transportation of the pulp is an impressive exercise.