Selective separation of zinc from germanium-bearing iron cake via a roasting–leaching process

Abstract

Germanium-bearing iron cake (GBIC) produced through the germanium removal process in a zinc smelter is a valuable source of zinc and germanium. However, achieving selective separation of zinc and germanium using pyrometallurgy treatment and sulfuric acid leaching methods is challenging. To address these challenges, this study introduced a novel roasting–leaching process. During roasting, willemite transformed into ammonia-soluble hemimorphite, promoting zinc leaching. This transformation was mainly attributed to the reaction between in situ water in GBIC and willemite within 200–500 °C. Optimal roasting conditions included a particle size range of 49–74 µm, a roasting temperature of 490 °C, and a duration of 4 h. Under optimized leaching conditions—[NH4++NH3] (7 mol/L), NH4+/NH3 molar ratio (2.5), temperature (50 °C), liquid-to-solid ratio (20 mL/g), agitation speed (600 rpm), and time (180 min)—zinc and germanium exhibited leaching yields of 84.92 % and 0.59 %, respectively, in an ammonia–ammonium carbonate system. After three cycles of leaching, the Zn concentration in leachate increased to 20 g/L, facilitating the subsequent recovery of zinc. Moreover, the Ge concentration in the germanium-bearing leaching residue increased by 1.5 times compared with the initial GBIC, making the residue a valuable source of germanium.