Biomass as a clean reductant for recovery of zinc from zinc leaching residue

Abstract

Detoxification and utilization of zinc leaching residue (ZLR) is a critical urgent problem for the zinc metallurgical industry. Traditional roasting methods relying on fossil fuels as reducing agents not only increase the operating cost but also contribute to environmental pollution. This work investigates the effectiveness of using biomass as the reducing agent for decomposing zinc ferrite in the process of ZLR roasting. Analysis methods including XRD, TG-DTG-DSC, and SEM-EDS are used to analyze the pyrolysis of biomass and the phase transformation and microstructural evolution of ZLR. The mechanism that biomass pyrolysis gas promotes the reduction of zinc ferrite in ZLR also is elucidated. The reduction rate of zinc ferrite can reach 43.87% under optimal reduction conditions when pine powder is used as the reducing agent. These optimal conditions include a reduction temperature of 750 °C, a biomass addition ratio of 0.75, and a reduction time of 90 min. It's believed that the reduction process mainly proceeds in the path of ZnFe2O4→Fe3O4→FeO→Fe. By using acid leaching, the extraction of zinc and iron from the reduction roast achieved 89.62% and 58.90%, respectively. During the biomass reduction process, loosely structured with abundant microcracks are obtained probably due to the reaction between the reducing gas and zinc ferrite particles. This study offers precious insights into the utilization of biomass for reductive roasting of ZLR with potential energy conservation and emission reduction.