Efficient recycling of spent Ni-Cd batteries through photocatalytic assisted leaching using TiO₂ nanopowder

This study introduces an innovative recycling method combining photocatalytic reactions with hydrometallurgy using a TiO₂ photocatalyst for spent Ni-Cd batteries recovery. Compared to traditional methods, a cost-effective process was developed with mild sulfuric acid (1 M H₂SO₄) at a low temperature of 25 °C. The effects of reaction time, TiO₂ photocatalyst dosage, and solid-liquid (S-L) ratio on leaching recovery were investigated and optimized using response surface methodology (RSM), resulting in high recovery percentages of Ni, Co, and Cd at 86, 97, and 96 %, respectively. Optimal conditions included a reaction time of 105 min, a TiO₂ dosage of 3.34 mg mL^-1, and an S-L ratio of 0.03 g mL^-1. By comparing leaching and TiO₂-assisted leaching, results showed that the presence of the TiO₂ photocatalyst under UV radiation improved the recovery percentage for Ni, Co, and Cd by over 27, 16, and 19 %, respectively. Kinetic analysis using the shrinking core model (SCM) indicated that in TiO₂-assisted leaching, the rate-controlling mechanism shifted from chemical control to diffusion control through the ash layer. The photoexcitation of TiO₂ generates reactive oxygen species and H⁺ ions, which synergistically oxidize and recover these metals efficiently. Results show that TiO₂ photocatalysis enhances reactivity, enabling faster and more efficient metal recovery through leaching. Overall, these research findings suggest a novel approach for utilizing photocatalysts in the leaching of secondary sources, resulting in enhanced process kinetics and optimal recovery rates at ambient temperatures and with low concentrations of milder acids like H₂SO₄.