The Vacuum Carbothermal Reduction Method Recovers Metal Indium From The ITO Waste Target

With the rapid development of electronic information technology,liquid crystal displays?LCD?are widely used,and the consumption of ITO targets,which are raw materials for the production of ITO thin films in liquid crystal displays,has also increased significantly.During the production of ITO thin film,the utilization rate of ITO target is only 30%,and more than 70%of ITO target becomes waste and needs to be recycled.The composition of the ITO target is generally indium oxide and tin oxide with a mass ratio of 9:1,and the metal indium content in the waste target exceeds 80%.The realization of green and efficient recovery of metal indium tin in waste targets is a major technical requirement for the development of the ITO industry.The current recovery of indium tin from ITO waste targets is mainly a hydrometallurgical process,which has the problems of long recovery cycle and large amount of acid consumption liquid in the process.According to the composition characteristics of ITO waste targets,vacuum carbothermal reduction is a green and efficient method for recovering indium tin with great application prospects.In this paper,according to the"vacuum carbothermal reduction-vacuum distillation"recovery and separation technology proposed by the research group,the vacuum carbothermal reduction method was systematically studied to recover metal indium tin from ITO waste targets.Firstly,the thermodynamic equilibrium between In₂O₃,Sn O₂ and C and the kinetics of carbothermal reduction of indium oxide were analyzed,and the temperature range of carbothermal reduction and the reaction control steps were obtained.Using pure indium oxide and tin oxide powder as raw materials,a carbothermal reduction experiment was conducted to find out the influence of various factors on the recovery rate of indium.Then,using the waste ITO target as the raw material,the influence of reducing temperature,time,ratio and other factors on the composition and properties of the reduced product was investigated.Finally,the optimized process conditions for the reduction of indium and tin by vacuum distillation of the reduced product were studied.The kinetic analysis of carbothermal reduction of indium oxide shows that the reduction mechanism of carbothermal reduction of indium oxide is the control model of nucleation and growth of crystals.Vacuum carbon thermal reduction experimental study of ITO waste target indicates the reduced indium tin alloy the content of metal indium in is 90.8%,and the content of metal tin is 8.9%at 900?,the amount of carbon added is 16wt%,10Pa?20Pa,60min holding-time,the particle size of ITO powder is more than 200 mesh.Consequently,the content of tin in the residue is higher than 99%and the content of indium is below 1%.The indium oxide and tin oxide in the waste target of carbothermal reduction ITO can be completely reduced to metal indium tin alloy.Vacuum distillation experiments indicates the recovery rate of indium is 96%and its purity reach 99.8%after distillation separation of indium tin alloy at 1250?,10Pa?20Pa,60min holding-time.Consequently,the content of tin in the residue is higher than99%and the content of indium is below 1%.This paper analyzes and establishes the kinetic model of carbothermal reduction of indium oxide,and obtains its reduction law.The research results show that the"vacuum carbothermal reduction-vacuum distillation"technology can achieve green and efficient recovery and separation of indium and tin from ITO waste targets,Provides a theoretical and practical reference for the recycling of ITO waste targets.