New Kinetical Aspects of Silver Recovery from Zinc Filter Cake Leaching in Hydrochloride Acid

Silver can be found in many minerals including zinc oxide minerals, but there is no report about its recovery from cold purification cake of zinc. Silver is reported as 80 ppm in this cake in addition of nickel, cadmium, and zinc. The purpose of this research is to determine the unknown kinetical aspects of silver recovery from leaching solution of this filter cake. After investigations of different dissolution systems, the oxidation leaching system using hydrogen peroxide as an oxidizing agent along with hydrochloric acid was selected for the silver leaching process, and the effective parameters were investigated. Utilizing the response surface method, the experiment’s design was carried out to identify the influencing factors, how they affect and optimize the leaching process, and the reaction’s kinetics. After conducting tests and optimizing the process, the feed was leached in a solution containing 1.5 M hydrochloric acid and 0.3 M hydrogen peroxide with a solid-to-liquid ratio of 0.075 g/cm³ at 38 °C in 25 min, and the silver leaching efficiency was determined to be 57.51%. The activation energy of the silver leaching process was 21.43 kJ/mol, and the chemical reaction mechanism was controlled leaching kinetics. The silver leaching rate can be increase up to 76.47% by using optimal reaction conditions and using sodium thiosulfate, copper sulfate, and sodium tricitrate as additives.