Microwave absorption and roasting characteristics of zinc sulfide concentrate

Abstract

A novel microwave roasting technology for formation of ZnO from zinc sulfide concentrate is presented. The dielectric properties and thermal behaviors of zinc sulfide concentrate and ZnS, CaO, MgO, ZnO, FeS, and ZnFe2O4, covering a temperature range of 25 to 1000°C at 2.45 GHz, are systematically investigated. The main microwave absorbing compounds are FeS and ZnS, while compounds like CaO, MgO, and SiO2 and other gangue exhibit poor absorbing properties. The sulfide concentrate temperature increase was divided into four stages, consistent with the dielectric properties. The morphology, phase and element contents of roasted were assessed covering the effect of roasting temperature, holding time, and particle size by SEM, XRD, and XRF. The optimal process conditions are roasting temperature 700°C, holding time 120 min, and the particle size less than 200 mesh. Microwave roasting mechanism shows microwave heat minerals (ZnS and FeS) selectively without heating gangue minerals (CaO, MgO, and SiO2), a significant temperature gradient develops between minerals. Thermal stress cause cracks effectively promote the dissociation of the monomers of useful minerals, increasing the interfacial area with O2, promoting the rate of desulfurization reaction. The work highlights harnessing microwave roasting as an effective and environmentally benign technology compared to conventional furnace technologies.