The Experiment And Mechanism Study Of Zinc Powder Replacement Method To Recover Silver From Thiosulfate Leaching Precious Liquor

With the promotion of the green development concept,the non-cyanide extraction technology of gold and silver continues to innovate.Thiosulphate method is considered to be the most potential alternative to cyanide method for gold extraction,which has the advantages of non-toxicity,rapid gold leaching and insensitivity to impurities.However,there has been a lack of a method for recovering gold and silver from the leaching solution of thiosulfate in a cost-effective manner at home and abroad.The replacement method is a hot topic at present.How to reduce the excessive consumption of reduced metal and effectively inhibit the coprecipitation of copper in expensive liquid are two important problems that this method faces in practice.In this thesis,the feasibility of replacing silver with zinc powder was investigated in the leaching system without ammonia thiosulfate.The conditional test mainly investigated the effects of[Zn]/[Ag]molar ratio,replacement time,reaction temperature,dissolved oxygen in solution,pH,etc.on silver substitution,copper coprecipitation and zinc powder consumption.SEM-EDS,EPMA,XRD and XPS were tested and analyzed under the optimal conditions.The study on the consumption law of zinc powder shows that the consumption of zinc powder in the replacement process is mainly affected by its dosage,replacement time and dissolved oxygen in the solution.The experimental results showed that the displacement effect was ideal under the conditions of[Zn]/[Ag]molar ratio 4:1,displacement time 20min,reaction temperature 298K,dissolved oxygen concentration less than 0.2mg/L,pH 8.6,and rotation speed 400 r/min.Under this condition,the recovery rate of silver can reach 99.44%,and the silver in the expensive liquid has been completely recovered,and the copper recovery was 49.23%.Displacement conditions are the key factors affecting the displacement effect.Increasing the[Zn]/[Ag]molar ratio,increasing the temperature,adjusting the pH of the solution,etc.can increase the recovery rate of silver and recycling effect,but also promote the co-deposition of copper.Controlling the dissolved oxygen concentration of the solution during the replacement process was advantageous for the replacement effect.Controlling the dissolved oxygen concentration of the solution during the replacement process is advantageous for the displacement effect,and the recovery of silver in a nitrogen atmosphere can ensure a high substitution rate while effectively reducing copper coprecipitation.The analysis of the replacement slag under the combination of the preferred test conditions showed that compared with the same zinc powder morphology,replacement of slag particles average particle size decreases,and increase the reunion phenomenon,this was due to the displacement in the process of zinc powder with the expensive liquid of silver ion,copper ion reaction,generated by the replacement product attached on the surface of zinc powder.The displacement slag mainly consists of Ag,Cu,Zn elements,a small amount of metal oxide Ag₂O,ZnO,and a small amount of metal sulfide.