Zinc Leach Residue Treated By Carbothermal Reduction And High Value Utilization Of ZnO Smoke

During the hot acid leaching stage of the Zinc hydrometallurgy,a large amount of leaching residues with complex composition and high-content value metals will be generated.The zinc leaching residue contains a large number of non-ferrous metals and rare elements,such as Zn,Pb,Fe,In,Ga,etc.It causes many environmental problems that cannot be ignored,including high toxicity and serious pollution.In this study,the zinc leaching slag has been disposed via the carbothermal reduction method.The main research contents and conclusions are given as follows:（1）The physical and chemical properties of zinc leaching residue have been investigated.The phases of the residue are mainly composed of ZnS,SiO₂,Fe₂O₃,KFe₃（SO₄）₂（OH）_6,and ZnFe₂O₄.The standard Gibbs free energy of all carbothermal reduction reactions that may occur have been calculated by FactSage the rmodynamics software.The results show that the Zn element in ZnFe₂O₄,ZnO,ZnS,Zn₂SiO₄ and ZnSO₄ can be reduced to zero-valent Zn.The zero-valent Zn volatilizes at high temperature due to its high saturated vapor pressure and then reacts with air to for m ZnO,implying that the element Zn enriches finally in the dust as ZnO.（2）The effects of reduction temperature,holding time,carbon ratio,and CaO addition on the volatility of Zn during the carbothermal reduction process have been studied.The results show that the Zn volatility reaches up to 97.31%under the optimal conditions―1250℃of reduction temperature,60 min of holding time,50%of carbon ratio and 10%of CaO addition.（3）The morphology and microwave absorbing properties of the as-obtained ZnO particles at different reduction temperatures（1200℃,1250℃and 1300℃）have been investigated.The results show that the ZnO particles obtained at 1200℃and 1300℃show the lamellar and island-like structure,and few clear-cut particles can be observed.The corresponding minimum reflection losses of these two samples are-5.23 dB at 8 GHz and-2.46 dB at 15.12 GHz,respectively.While ZnO particles obtained at 1250°C with rod and spherical shapes exhibit-25.56 dB of the minimum reflection loss at 15.84 GHz with 5 mm of thickness.（4）The nitrogen-doped graphene（NG）/ZnO composite has been designed to study its electrochemical performance.The results show that NG/ZnO can be used as an anode,and its current discharge capacity reaches up to 594.5 mAh g^-1 at a current density of 500 mA g^-1,which is much higher than that of the traditional graphite anode(theoretical capacity 372 mAh g^-1).Its reversible specific capacity can maintain221.7 mAh g^-1 after 210 cycles.This provides a new exploration way for the reuse of components in nonferrous metal waste residue.