Leaching behavior and process optimization of tin recovery from waste liquid crystal display under mechanical activation

Abstract

Recycling Sn from waste liquid crystal display (LCD) is crucial to alleviate resource shortage and prevent environmental pollution. However, the disposal of waste LCD is a complex coupling process affected by multi-factors. The lack of mature harmless and resource-based treatment process restricts the development of industrialization. Therefore, an environmentally sound process focusing on resource recovery was proposed to recover Sn efficiently and remove toxic substances from waste LCD in this study. The reaction mechanism and leaching kinetics were discussed assisted by mechanical activation, and the statistical and mathematical method (Box-Behnken Design (BBD) model) was adopted to optimize the leaching process. The results showed that the mechanical activation could improve the physical and chemical properties of ITO glass. The essence of the leaching reaction mechanism was that the H+ in H2SO4 combined with O2− in the lattice of In2O3 to form OH−, resulting in Sn–O bond broking and Sn4+ entering the aqueous solution. Furthermore, the Zeta potential results showed that the Zeta potential of SiO2 particles less than 0.035 mm was close to zero near pH 2, resulting in agglomeration between SiO2 particles under the action of Coulomb force. The leaching kinetics was well expressed by the shrinking core model. The BBD model showed satisfactory correlation between the predicted and actual results, and the particle size was the most critical factor affecting the leaching efficiency. The maximum leaching efficiency was 87.6% which was obtained under the following optimal condition: 6 mol/L H2SO4, 108 min, 88 °C, and 0.035 mm ITO glass powder. Our findings demonstrated that the developed recovery process was both efficient and environmentally sound, which had the potential in the industrialization of waste LCD recycling system.