Mechanism Of Zinc Replacement For Silver In Ammonia-free Thiosulfate Noble Liquor

Zinc replaces precious metals from the ammonia-based thiosulfate leaching precious solution,which has the advantages of convenient operation,fast replacement rate,and high efficiency.However,due to the influence of the copper ammonia complex ion in the solution,the amount of zinc is relatively high.Zinc replaces silver in the precious solution of ammonia-free thiosulfate leaching,avoiding the influence of copper-ammonia complex ion and greatly reducing the amount of zinc.Zinc powder replacement has achieved a good recovery effect,but its reaction mechanism is not clear.Therefore,studying the cementation process and explaining the cementation mechanism are very important for the popularization and application of this technology.In this paper,zinc as a cement agent.Through the study of zinc plate replacement of silver thiosulfate complex ions and copper thiosulfate complex ions kinetics,combined with thermodynamic calculation,electrochemical test,cementation product morphology and composition analysis.The reaction mechanism of zinc replacement for leaching silver in precious liquor without ammonia thiosulfate is deduced,and a reaction model is constructed.The silver and copper in the ammonia-free thiosulfate leaching silver solution mainly exist in the form of thiosulfate complex ions.Thermodynamic calculations show that zinc can spontaneously replace silver and copper from the thiosulfate solution.The kinetic study shows that zinc replaces silver and copper from the ammonia-free thiosulfate leaching solution,and the cementation process follows the first-order kinetic equation.The replacement of silver thiosulfate complex ion is divided into two stages,and the replacement of copper thiosulfate complex ion is divided into three stages.The rate of replacement of copper thiosulfate complex ion is faster.The elemental copper replaced by zinc can be used as a cement agent to synergize with zinc to replace silver thiosulfate in the precious liquid,thereby increasing the deposition rate of silver.The presence of sulfur oxygen ions such as thiosulfate,sulfate,sulfite and tetrasulfate will cause a trace amount of zinc to dissolve,and trace amounts of zinc oxide,zinc sulfide,silver thiosulfate complex ions and copper thiosulfate complex ions are attached to the surface of the zinc powder.Ions will also react with them to form small amounts of silver and copper oxides and sulfides,but they will not have a significant impact on the replacement.The final product of replacement is elemental silver and elemental copper.Zinc replaces the silver thiosulfate complex ion,and silver is deposited as a simple substance.Zinc replaces the complex ions of copper thiosulfate,and copper first forms a copper-zinc alloy,which further reacts with copper thiosulfate,and finally turns into elemental copper.The deposited copper and silver cover the zinc surface and can fall off from the zinc surface,exposing the new surface to continue the displacement reaction.This dissertation studies the mechanism of zinc replacement of silver from ammonia-free thiosulfate precious liquor,which has guiding significance for the development of the recovery of precious metals from thiosulfate precious liquor.