Pb-based aggregate, Ge-galena coexistence, and Ge-anglesite coprecipitate-Limitations and an improvement of germanium recovery from secondary zinc oxide via H2SO4 leaching

Germanium is a strategic resource for its unique physical and chemical properties; however, the unsatisfactory recovery efficiency of germanium from secondary zinc oxide is a problem for pertinent smelters, as well as an obstruction for circular economy of germanium. Certain limitations related to germanium recovery from secondary zinc oxide were recently discovered using a variety of techniques, including scanning electron micro-scopy, sulfuric acid and sodium acetate selective dissolution, transmission electron microscope and selected area electron diffraction, electron probe microanalysis, and essential experimental analysis. A manganese dioxide-based (one-step or stepwise) leaching process (ML) is proposed, evaluated, and compared with oxygen pressure leaching and nitrate leaching. Results indicated that wurtzite was the limiting factor for zinc leaching, and that the lost germanium was trapped in Pb-based spherical aggregate, galena, and anglesite. In an ML process conducted with manganese dioxide dosages of 7.5-10 wt% at 90 degrees C for 60 min, the leaching % of germanium and zinc reached 96-98%. This ML process was found to be compatible with zinc hydrometallurgy and conducive to a complete utilization of resources that enable a further reduction of the solid waste produced by zinc metallurgy.