Zinc Recovery from Spent Chemical Sorbent by Dry Chlorination and Electrodeposition from Chloride Solutions

Spent catalysts, chemical traps and sorbents are types of solid wastes generated worldwide, which contain potentially valuable or environmentally hazardous materials that need to be recovered before final deposition. Chlorination and electrolysis are unit processes applied in extractive metallurgy for metal extraction from poly-metallic or low-grade ores. The primary aim of this study was to assess the possibility of applying pyrometallurgy (chlorination) and electrometallurgy to spent chemical sorbents used as sulfur traps and to recover zinc. The spent sorbents may include zinc in different phases: ZnO, ZnS and Zn0.65Al 0.35(OH)2(CO3)0.167(H2O)0.5. It was found that 96.8% of the zinc can be separated by dry chlorination at 475ºC with pure chlorine. Before chlorination, addition of CaCO3 (17 wt.%) is necessary to prevent formation of ZnSO4. The zinc chloride obtained is dissolved in water and electrolyzed to generate chlorine which can be recycled to the chlorination reactor, and metallic zinc as a non-adherent layer on the cathode. The electrolyte composition is 65 g.L−1 ZnCl2 with 20 g.L−1 H3BO3 and 200 g.L−1 KCl. It is possible to recover pure zinc (99.9 wt.%) from chemical sorbents with the methodology proposed. These results are important for the development of new and more efficient recovery strategies to prevent environmental damage and obtain valuable elements from wastes.