Synchronous extraction of Mn, Pb, Sn, and Se from hazardous electrolytic manganese anode slime (EMAS) via sulfidation transformation and leaching: Rapid separation and sulfidation mechanism

Abstract

Based on the chemical affinity with sulfur, and solubility and volatility differences of the sulfurized transformed phases, sulfidation treatment of refractory hazardous solid waste can effectively recover valuable metals. In this work, a technically reasonable and efficient treatment of hazardous electrolytic manganese anode slime (EMAS) for rapid and synchronous manganese (Mn), lead (Pb), tin (Sn), and selenium (Se) separation via sulfidation transformation and leaching was proposed. After sulfidation, the valuable elements in EMAS were selectively separated in which the Mn and Sn were converted to soluble salts, whereas Pb was transformed to insoluble sulfate and most Se was volatilized. 70% Se was collected from the volatile dust, 98.1% Mn and 80.5% Sn were transferred to the leachate, while 99% Pb was kept in the leaching residual as the EMAS was treated after sulfidation transformation followed by sulfuric acid leaching under the optimized conditions: roasting with a sulfur/EMAS mass ratio of 1:1 at 400℃ for 10 min, followed by leaching under a sulfuric acid concentration of 8%, a liquid/solid ratio of 10:1, and a stirring rate of 100 r/min at 25℃ for 5 min. Sulfidation kinetics indicated that the sulfidation of manganese oxides was controlled by the interfacial chemical reaction with an activation energy of 35.367 kJ/mol. In terms of efficiency, the low-temperature sulfidation roasting within 10 min and dilute sulfuric acid leaching within 5 min for synchronous separation indicated that the proposed process was reasonable and efficient for hazardous EMAS treatment. For environmental protection, the detrimental SO2 byproduct can be returned to the sulfidation roasting process to reduce the tetravalent manganese or used to make sulfuric acid. The sulfidation and leaching mechanisms for Mn, Pb, Sn, and Se separation were also discussed in detail in this work.