Unraveling synergistic control in green Leaching: A double exponential kinetic model for efficient and sustainable indium recovery from E-waste using deep eutectic solvents.

The rapid development of the electronics industry caused an exponential increase in waste liquid crystal displays (LCDs). Waste LCDs release indium tin oxide (ITO, In2O3·SnO2), which is cytotoxic and poses a significant burden on the environment. Deep eutectic solvents, characterized by their high saturated vapor pressure and tunable composition, were regarded as sustainable green solvents and could serve as efficient and environmentally friendly leaching agents for ITO. This study systematically investigated the leaching mechanism of indium tin oxide in a specific DES (oxalic acid dihydrate: choline chloride = 1:2.6). Characterization results revealed a multi-step pathway with multiple rate-controlling stages. The proposed double exponential model demonstrated exceptional performance (R2 > 0.995) and stability across all conditions, effectively describing this multi-controlled process. Using this model, the effects of temperature, stirring rate, and indium tin oxide particle size were quantified. Dynamic analysis confirmed the dual control mechanism. Significantly, reducing particle size drastically lowered apparent activation energy (265 μm: 53.24 kJ·mol-1 → 45 μm: 18.02 kJ·mol-1), highlighting its key role in efficiency, while stirring rate had minimal impact. The model's broad applicability was validated across diverse deep eutectic solvent leaching systems (R2 > 0.98). This work pioneers the application of the double exponential kinetic model to deep eutectic solvent leaching, establishing it as a powerful tool for understanding mechanisms and optimizing processes.