Recovery of heavy metals from waste Ni-Cd batteries in subcritical water using waste CPVC

Proper disposal and efficient recovery of used Ni-Cd batteries are paramount to ensuring a greener and more sustainable future. Although waste battery recycling has been widely studied, the environmentally friendly and cost-effective recovery of heavy metals from spent Ni-Cd batteries remains a challenge. In this study, waste chlorinated polyvinyl chloride (CPVC) was applied for the first time as a source of HCl in a subcritical water extraction (SWE) process to accelerate leaching and improve recovery efficiency. Under optimised conditions of 300 °C, 90 min, 15 mL/g L/S ratio, and a 1:3 Ni-Cd battery powder/CPVC mass ratio, recovery rates exceeded 98.23 % for Ni, 95.61 % for Cd, and 99.98 % for Co. Kinetic analysis indicated that the dissolution followed a surface chemical reaction control model with high correlation (R² = 0.93-0.98), while activation energies of 47.34, 58.77, and 62.99 kJ/mol for Ni, Cd, and Co demonstrated that CPVC-assisted SWE is less energy-intensive than conventional acid leaching. This approach provides two key benefits: CPVC valorizes plastic waste while replacing hazardous mineral acids, and SWE improves heat and mass transfer, enabling faster kinetics and environmentally safe recycling. The overall findings highlight an effective, economical, environmentally benign, and green technique for recycling spent Ni-Cd batteries.