Enrichment And Separation Of Indium From ITO Film Etching Waste Liquid By Solvent Extraction

Indium tin oxide(ITO)is widely used in solar cells and liquid crystal panels due to its high electrical conductivity and visible light transmittance.In the process of ITO film etching,a large amount of etching waste liquid is produced.The waste liquid contains a variety of rare earths,such as indium,tin,molybdenum,etc.,It will cause environmental pollution if discharged directly.There is little indium in nature,and with the rapid development of the electronics industry,the demand for indium has increased sharply,so the recovery of indium from etching waste liquid is particularly important.In this paper,recovery of indium from ITO etching waste solution by solvent extraction was systematically studied.After comparing the advantages and disadvantages of various rare earth metal extractants,P204 was selected as extractant and sulfonated kerosene as diluent.Firstly,the single factor experiment of extraction was carried out to obtain the optimal extraction conditions as follows:temperature 25℃,stirring speed 864 r/min,mixing time 5 min,volume concentration of P20420%,initial acidity of the aqueous phase pH=0.5,and phase ratio O/A=1:60.Under the optimal extraction conditions,the extraction rate of indium was 92.76%after single extraction,and the concentration of indium in the organic phase was 5.727 g/L.Compared with the concentration of 0.109 g/L in the waste solution before extraction,the concentration of indium increased by 56 times.Then the single factor experiment of stripping was carried out to obtain the optimal stripping conditions as follows:concentration of hydrochloric acid 4 mol/L,mixing time 8 minutes,and phase ratio A/O=1:8,Under the optimal stripping conditions,the stripping rate of indium was 98.83%,and that of tin was 0.After stripping,the concentration of indium was 45.28 g/L,which was 415 times higher than that in the waste solution.The total recovery of indium was 91.68%,and realized the separation of indium and tin.The experiments on recovery of indium was carried out on high concentration and more complex composition of etching waste liquid.The results showed that the phase ratio of extraction O/A=1:7 and phase ratio of stripping A/O=1:6 were the best conditions.After single extraction and stripping,the concentration of indium was 44.06 g/L,which was 34 times higher than the initial concentration of indium in the waste solution,and the total recovery rate of indium was 97.23%.It was proved that the method is suitable for different etching waste liquid.In addition,the selectivity of P204 to indium,tin,molybdenum and aluminum was studied.The results showed that the smaller the phase ratio of extraction was,the more favorable the separation of indium from Sn and Al was,and the separation of indium from other metals can be achieved by controlling the concentration of stripping agent.The equilibrium isotherm of extraction and stripping was obtained.When phase ratio O/A=1:6 and the concentration of indium in the etching waste solution is 1.932 g/L,the theoretical stage of countercurrent extraction is 2 determined by the extraction equilibrium isotherm.According to the theoretical stage,the actual extraction stage was estimated to be three stages,and a cascade experiment with 9 rows and 27 extractions was designed to simulate the three-stage countercurrent extraction process.The results showed that the indium can be completely enriched in P204+sulfonated kerosene extraction system after two-stage countercurrent extraction.The extraction rate was about 83.8%at stage 1 and nearly 100%at stage 2.After extraction,the concentration of indium in the organic phase was more than 11.5 g/L.Compared with single extraction,the concentration of indium in the organic phase was greatly increased,and the extraction stage and concentration distribution of indium at all stage were obtained.