Leaching Of Gold In NaCl-NaClO-H₂O System From Low-grade Gold Ore

With the rapid development of economy and the continuous improvement of people’s living standard, the contradiction between people’s overall demand for gold and the supply is more and more sharply, and resource shortage has become the main factors of non-ferrous metals industry development in our country, so the low grade gold ore, solid waste and other secondary resources development has become an important aspect of non-ferrous metals industry resources in our country. At the present stage, leaching by cyanide solutions is the main process for gold extraction. It has been used in industrial application. But with this method available for so many years, a series of recent environmental problems appears around the world. So finding out a reasonable and effective non cyanidation method to leach gold from low-grade gold ore has considerable benefits not only to the economy but also to the environment.The research object (low grade gold) of this article is provided by Zhaoyuan of Shandong province, a new technology of non cyanidation leach of gold was successfully developed after the comprehensive investigation on mineralogy, the process consists of two parts, as follows:leaching of gold in NaCl-NaClO-H2O system from low-grade gold ore; adsorption of [AuCl4]-from leaching solution in NaCl-NaClO-H2O system onto the activated carbon. The main research contents were as follows:leaching process conditions, adsorption process conditions, the leaching kinetics, the adsorption thermodynamics and kinetics, etc. XRF, XRD, SEM-EDS and FTIR were used to study the samples of the low-grade gold ore before and after the leaching of gold, and the samples of activated carbon before and after the adsorption of [AuCl4]-, ideal results were obtained. The conclusions were as follows:(1) with the study of NaCl-NaClO-H2O system leaching of gold from low grade gold ore, and the optimum conditions was proved as follows::10:1 for the liquid-to-solid ratio,-450+150 μm for particle size,400 rpm for stirring speed,4 h for leaching time,50℃ for the leaching temperature,4mL NaClO,300g/L NaCl and 8mL HCl. The results show that the gold leaching rate can reach 89.79% under the optimum conditions. Leaching kinetics indicate that diffusion through the product layer is the rate controlling process during the leaching process. The kinetics equation is 1-2/3R-(1-R)2/3= 0.043796 t. The activation energy was determined to be about 5.40kJ/mol. Verified by experiment, the model can describe the actual reaction process and explain the leaching mechanism well.(2) Different process parameters which was in the adsorption of [AuCl4]- onto activated carbon have been studied, and the optimum conditions was as follows:313.15k for adsorption temperature,90min for adsorption time,200 rad/min for adsorption rotating speed, 1.075g/L for initial concentration of [AuCl4]- and 0.20g for the amount of activated carbon. And the adsorption rate of [AuCl4]- is up to 94.93% finally under the optimum conditions. Langmuir model is suitable for this adsorption process more than Freundlich model. The process of [AuCl4]- adsorption onto activated carbon is spontaneous and physical in nature. [AuCl4]- adsorption followed the pseudo-second-order kinetic model. With adsorption mechanism study it is proved that intra-particle diffusion is the rate controlling step. Coconut Shell activated carbon was proved to be quite applicable with the gold leaching solution which was produced by the research that use NaCl-NaClO-H2O system to leach gold.