Study Of The Trials And Mechanism Of Leaching Refractory Gold And Silver Ore In Green Technology

As an important method of gold extraction by free-cyanide reagents, the thiosulfate process has many virtues: being not poisonous, inaction to impurities, high speed and the better leaching rate, so the thiosulfate process is paid more and more attentions. But there are also several un-ignorable problems: ?it must be heated in most situations, and the temperature range is also very small, so it is not controlled validly. ?the consumption and the cost of the thiosulfate is very high. So, it' s very important for thiosulfate leaching to optimize the technology at normal temperature and pressure and to decrease the thiosulfate consumption.The experiment shows that, at normal temperature and pressure, the ratio of liquid to solid, stirring speed, leaching time, pH, the concentration of S2O32-, SO42-, Cu2+ and SO32-, the adding quantity of NH3 H2O are the main factors affecting the gold leaching rate, Then the optimum operating conditions are obtained according to the feasibility of gold leaching with thiosulfate process in technological and economic performance: the ratio of liquid to solid is 3:1; pH=9.70; the leaching time is 4~6h; the concentrations of Na2S203 5H2O, (NH4)2SO4 and Na2SO3, are 65g/l (0. 262M S2O32-), 30g/l (0. 227M SO42-) and 30 g/1 (0. 238M SO32-) respectively; cupric ions are only needed for the materials without copper; when the total consumption of ammonia is not excessive, NH3 H2O can be added appropriately.From a new angle, the regularities of thiosulfate consumption are studied completely in simulative and actual situation respectively. Effects of pH, stirring speed, Cu2+ and ammonia on the stability of thiosulfate are investigated in order to find out the regularities of thiosulfate consumption. Then effects of adding different regents and metalion on the stability of thiosulfate are also studied. Consequently, the loss of thiosulfate during leaching, cementation laying up processes has been examined experimentally. The loss of thiosulfate is very low under well-controlled conditions.The paper discusses further the mechanism of leaching gold by thiosulfate, also gives relatively clear explains and analyses to some obscure recognitions. In the thesis, author has deduced the thermodynamic criterion of the gold thiosulfate leaching at first, and we have suggested that an oxidant will improve gold leaching proceed as long as the electric potential of an oxidant is over -0. 128V in the light of thermodynamics. The criterion of the equilibrium: lgK 298 =16.935n( +0.128) is also given. These studies of the technology and mechanism about leaching gold by thiosulfate present a valuable reference for the further research.