[Division of U.S. 3,574,600 (Ca 74:129,265x)] the recovery of au from lean carbonaceous ores by conventional cyanide treatment to take au(cn)2- into solution is greatly improved by first treating such ore slurry with hypochlorite of na or ca to destroy, before cyaniding, the ability of the organic impurities in the ore, such as humic acid, to absorb au(cn)2-. This treatment is especially effective in dense slurries having about equal parts of h2o and ground ore at 50 deg.-60 Deg. C. Lime can be used to enhance the treatment, but is not necessary. The naocl can be formed in the slurry by electrolysis of brine used as the liquid phase. When 100 g of ore containing 30 oz au/ton and 4.8 pct c, 0.48 pct of which was organic, was slurried with 150 ml h2o, and heated to 60 deg. C with 1 g each of cao and naocl, and after 1 h 0.5 G more naocl was added with continued heating for 6 h, followed by the addition of 0.1 G nacn and stirring 24 h, 96 pct of the au was extracted into the solution. Without the naocl pretreatment, the au extraction by conventional cyaniding was 25 pct. Such ore untreated by naocl absorbed substantial amounts of au(cn)2- in a few hours, when, with or without kerosine, it was in contact with an aqueous solution of au(cn)2-.
U.S. Pat. 3,639,925; Feb. 8, 1972; Chem. Abstr. 77:8,584D