The application of selective leaching and complex anion exchange in a novel aqueous process to produce pure indium from waste liquid crystal display panels

By studying the leaching kinetics of indium from waste liquid crystal displays (LCD), it was pointed out, that recoveries of > 90 % are possible with 0.5 M HCl at 80 °C or 2 M HCl at 55 °C. The anion-exchange sorption of indium was found practically negligible from sulphate solutions, however, in chloride solutions of 2 mol/dm3 HCl (or NaCl) indium was moderately sorbed (log D = 0.83), and a further increase of the distribution coefficient (log D = 1.1) was found until 6 mol/dm3 Cl- ion concentration. Based on the determined activation energies, at low (< 1 M) HCl concentrations, the process is controlled by the formation of the complex species, while above, diffusion and transport processes are more important. The devised chromatographic separation in an anion-exchange column was able to eliminate virtually all the practical impurities. After loading the leachate of 5 mol/dm3 chloride ion concentration, the non-sorbed alkali, alkaline earth and some transition metals can be removed by rinsing the resin bed with a solution of 2 mol/dm3 chloride ion concentration. Indium can be eluted by reducing the chloride ion concentration in the influent to 0.25 mol/dm3. The still retained elements (Zn, Sn, Bi) can be removed with 1 M NaOH solution. The pure solution was used to electrowon indium metal, which was analysed by SEM-EDS and - after dissolution – with ICP – OES. The purity of the metallic indium product was found to be 99.9997 %.