Leaching behavior of indium from waste liquid crystal display: Further study on the coupling effect of multi-factors for optimum leaching process

Abstract

Recovering indium is vital for alleviating the indium resources shortage and eliminating environmental pollution while treating the hazardous liquid crystal display. However, effective recovery of indium has been affected by the multi-factors, which have a coupling effect. Therefore, an environmentally sound process focused on resource recovery was proposed to remove or separate toxic substances and efficiently recover the indium by acid leaching. The leaching kinetics and mechanism of indium were investigated, and the leaching process with the coupling effect of multi-factors was optimized by utilizing the Box-Behnken design (BBD) model. The experiment results suggested that the leaching kinetics were dominant by the chemical reaction control in the initial reaction stage, and the internal diffusion control was dominant in the later stage. The indium leaching process was conformed to the shrinking core model and a macroscopic kinetic equation was established. The BBD model expounded that the ITO glass particle size and leaching temperature had the most significant effect than other variables during the leaching process. However, the leaching efficiency decreases at a particle size less than 35 µm. The optimum leaching processing conditions were as follows: leaching time of 109 min, leaching temperature of 87 °C, the mean particle size of 35 µm, and sulfuric acid concentration of 5.3 mol L−1, obtaining an indium leaching efficiency of close to 99%. Furthermore, it was verified that the experimental result under the optimal condition was conformed to the predicted result of the BBD model.