Process Development for Extraction and Separation of In and Y from Discarded Flat Panel Displays

Doktorsavhandling, 2015

From the time of their invention in the 1970s, flat panel displays (FPDs) have slowly become the most used type of displays in televisions, computers, and cell phones. A major subgroup of FPDs is lLiquid crystal displays (LCDs). With the continuous growth of FPDs, the need and incentive to recycle the valuable components has also grown larger, as the displays will inevitably enter the waste stream. Among the valuable components, indium from the transparent electrode coating on LCD glass and rare earth elements (REEs) from parts such as fluorescent lamp phosphors are of special interest for recycling from end-of-life products. In this work, hydrometallurgical processes to recycle indium and REEs such as yttrium from different types of FPD waste were developed. The process comprised several steps such as leaching and solvent extraction. Result of the leaching studies showed that concentrations of metals such as iron and copper were much higher indium and yttrium. Furthermore, with respect to leaching efficiency and feasibility of subsequent solvent extraction process, 1 M H2SO4 was determined as the best leaching option for the recovery of indium from LCD glass and 1 M HCl for the recovery of both indium and yttrium from mixed FPD waste. Several choices of aqueous and organic solutions were tested in a solvent extraction screening test to determine feasible choices of extractant and stripping agent. The results showed that extraction from H2SO4 using DEHPA in kerosene followed by back-extraction with HCl was a promising alternative for the recovery of indium. Indium and yttrium can be separated by selective extraction of indium from chloride media using Cyanex 923. In order to further optimize the separation process, the effect of pH and temperature on the extraction of indium was investigated with H2SO4 or HCl as the aqueous phase and DEHPA in kerosene as the organic phase. From the temperature study it was concluded that the since the extraction of indium was an exothermic process, optimal extraction temperature was 20 oC. Furthermore, a process scheme was proposed for the recovery of indium and REEs from 1 M HCl leachate. This process was tested using laboratory mixer-settlers and was found to agree reasonably well with theoretical calculations based on the extraction isotherms of indium and yttrium.