Study On The Indium Recovery Process From Waste Liquid Crystal Displays And Related Key Technologies

With the discard of liquid crystal displays (LCD), the treatment technologies on thewaste LCDs are in urgent need. Current disposal methods mainly include landfill andincineration, which not only generate serious environmental impacts, but also cause thewaste of resources. In this thesis, a new process combined pyrolysis and acid immersionwas proposed to focus on the comprehensive treatment of the ITO glass module in orderto achieve maximal reduction and recovery of the waste LCDs.In this thesis, pyrolysis was used to dispose the organic component of waste ITO glassmodules. By studying the pyrolytic characteristics and product properties, it can be foundthat the highest yields of liquid products of ITO glass module and polarizing film wereboth obtained at the final pyrolysis temperature of450°C, which were7.20%and50.45%respectively. And at this final pyrolysis temperature, the gaseous products of them weremainly composed of H2, CO, CO2, CH4and a small amount of C2H6, C2H2. The liquidproducts mainly contained acids, esters and aromatics were necessary to be upgradedsuch as hydrotreating process before used as fuel source or industrial feedstock due to thehigh O/C and low HHV. The apparent kinetic study showed that the pyrolysis processesof both were mainly controlled by the chemical reaction mechanism.Aiming at the acid immersion process of indium from ITO glass, the influence of thesingle factors, such as temperature, time, acid concentration and liquid/solid ratio, wereexplored and the thermodynamics and kinetics were also studied in this thesis. Theoptimization of indium recovery by acid immersion was investigated using responsesurface methodology. A second order polynomial equation was obtained to predict theindium recovery (R2=0.9985). Meanwhile, the response surface plots revealed that thetemperature played a more dominant role on the effect of indium recovery compared withthe time and acid concentration variables. By using desirability function, the optimumprocessing condition was obtained with time42.2min, temperature65.6°C and acidconcentration0.6mol/L, which gave the indium recovery closed to100%. In this thesis,the multistage and countercurrent acid immersion processes were also studied and theresults showed that two-stage countercurrent acid immersion process can recover indium from ITO glass efficiently while reducing the temperature and acid concentration therebysaving the energy consumption and cost.By comparing the purification and concentration methods of NaOH precipitation,Na5P3O10precipitation and extraction, it was showed that the methods of NaOH andNa5P3O10precipitation were difficult to obtain the effective separation of metal ions inthe leaching solution. In contrast, P204and P507extraction can achieve the purificationand concentration of indium.In this thesis, the underpotential deposition (upd) of indium on Pt electrode was studied.The results showed that the upd-In deposited on the Pt disk electrode surface can promotethe methanol oxidation, which provide a new idea on the indium utilization.