Electrochemical behavior of gold cyanidation in the presence of a sulfide-rich industrial ore versus its major constitutive sulfide minerals

A detailed study on the relative importance of passivation phenomena and galvanic interactions during gold cyanidation was carried out. Mineral disc electrodes consisting of a sulfide-rich industrial ore and major sulfide components were prepared along with an Au electrode (gold/silver alloy) in use for gold leaching rate tests. These leaching tests that were conducted by hyphenating gold and mineral disc electrodes conjointly in one electrochemical cell or in two separate electrochemical cells objectified both passivation-induced setbacks as well as boosts by Au/mineral galvanic interactions on gold dissolution. To decipher the role of sulfide ores on gold cyanidation, a systematic study was performed by monitoring the leaching behavior of an Au disc electrode successively immersed in slurries of industrial ore and its major sulfide constituents, i.e., pyrite, sphalerite and chalcopyrite. The tested mineral constituents and ore exhibited an inhibiting effect on gold leaching, decreasing in the following order: chalcopyrite > sphalerite > industrial ore > pyrite. Pre-oxidation of the industrial sulfide ore prior to cyanidation improved the gold leaching rate. However, in spite of noticeable reductions in cyanide consumption, no beneficial effect of pre-oxidation on gold leaching was observed for the major sulfide (ore) constituents when tested separately. Although cooperating permanent galvanic interactions between gold and main constitutive minerals in the industrial ore prompted higher gold leaching rates, predictability of the latter from lab-controlled leach tests of the nearly pure constitutive sulfide minerals still remain premature.