چكيده به لاتين
Nowadays, the shortage of primary resources, especially in Iran, has led to the recovery of many valuable elements from secondary resources such as waste generated from mineral processing factories. The cold purification filter cake from zinc smelting industry is one of these wastes, which contains valuable metals such as nickel, cadmium, and silver. Silver is one of the expensive metals, and economically, it is cost-effective to recover these elements from secondary resources. The aim of this research is to dissolve the existing silver in the cold purification filter cake from lead and zinc factories located in Zanjan province, which after crushing and grading, was used as the primary feed. After acid digestion, the amount of silver in the primary feed was reported as 80 ppm. After examining various leaching systems, the oxidative leaching system using hydrogen peroxide as an oxidizing agent, along with hydrochloric acid, was selected for the leaching process, and the effects of the presence of sodium thiosulfate, copper sulfate, and trisodium citrate were investigated. The experiment was designed using the response surface methodology in two stages to identify the influential factors, their effects, and to optimize the leaching process. The reaction kinetics were also investigated in each stage. After conducting the experiments and optimizing the process in the first stage, the primary feed was dissolved in 1.5M hydrochloric acid solution, a solid-to-liquid ratio of 0.075 gr/mL, a temperature of 37°C, and a time of 25 minutes, and the leaching efficiency of silver was determined to be 57.51%. The results indicated the compliance of the shrinking core model with the small particle size and the control mechanism by chemical reaction on the leaching efficiency of silver. The activation energy of the silver leaching reaction in the first stage was calculated to be 21.43 kJ/mol. In the second stage, the effects of thiosulfate, copper sulfate, and trisodium citrate as additives, in addition to the optimal parameters of the first stage, were investigated by experimental design, and the leaching efficiency of silver increased to 71.34%. The optimal concentrations of sodium thiosulfate, copper sulfate, and trisodium citrate were determined to be 0.0375M, 0.00125, and 0.0375 M, respectively, and the amount of hydrogen peroxide was 7.5 mL. The activation energy of the reaction in the second stage was calculated to be 18.81 kJ/mol. The results of this study showed that the use of the mentioned additives along with the oxidative leaching system not only increases the leaching efficiency but also reduces the activation energy of the reaction.
