Kinetic regularities of hydrometallurgical recycling of spent displays: behavior of indium

This article discusses the physicochemical regularities of indium leaching from the surface of glass plates of used displays in various acids. The glass of used displays was pre-cleaned from polarizers and crushed. Their base is comprised of silicon and aluminum oxides. Indium is presented in the form of In₂O₃·SnO₂. Indium content in the material obtained is 174.8 mg/kg. Individual solutions of sulfuric, hydrochloric and methanesulfonic acids were used as leaching agents. The influence of concentrations of the mentioned acids (0.1–1.0 N), leaching duration (10–60 min), temperature (298–353 K) and liquid-to-solid ratio (L : S = (7.5÷15.0): 1 cm³/g) on the degree of indium extraction into solution has been determined. Partial orders of reaction in terms of CH₃SO₃H, H₂SO₄, HCl are 0.69, 0.67 and 1.10, respectively. In the course of experiments an intensive increase in indium concentration was observed in the first 20–40 min f leaching in H₂SO₄ and HCl solutions. The process rate then decreased and indium extraction actually did not increase, due to a fall in the amount of non-reacted indium. During leaching in 0.1–0.4 N in CH₃SO₃H solutions, the rate of indium dissolution did not change throughout the experiment, since the amount of non-reacted indium gas decreased insignificantly. The acids considered here can be ranked in the following ascending order of their efficiency for indium dissolution: CH₃SO₃H, H₂SO₄, HCl, which corresponds to the growth of strengths of these acids. An increase in the temperature led to a significant increase in indium extraction. The apparent activation energies of In₂O₃ dissolution in CH₃SO₃H, H₂SO₄, HCl solutions have were calculated as equal to 51.4, 51.2, 43.4 kJ/mole, respectively. It was established that with the use of HCl as leaching agent, the increase in the fraction of liquid phase in the slurry from 7.5 : 1 to 15 : 1 cm³/g lead to fall in indium extraction by 2.4 times and the initial leaching rate by 3.2 times. It was demonstrated that an increase in L : S during indium dissolution in CH₃SO₃H (from 7.5 : 1 to 15 : 1 cm³/g) and H₂SO₄ (from 10 : 1 to 15 : 1 cm³/g) is accompanied by insignificant changes in extraction and initial leaching rate. Therefore, the studies performed demonstrated that indium leaching from glasses of spent displays flows in mixed mode upon the use of HCl and in kinetic mode in H₂SO₄ and CH₃SO₃H solutions.

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