Subcritical water delamination: A promising path to efficient recycling of critical minerals

The objective of this study is to degrade the polymer layers within crystalline silicon (c-Si) photovoltaic modules and delaminate the essential valuable minerals for recycling, employing solely the thermodynamic attributes of water under subcritical conditions and abstaining from the utilization of chemical solvents. The c-Si wafer was successfully delaminated from the polymer structures at 200 degrees C, 100 bar for 30 min in a high-pressure reactor and ground in a planetary ball mill, where the experimental conditions were optimized for energy consumption using a Box-Behnken design. Hydrothermal subcritical delamination process provides structural changes in the polymer layers due to swelling of the ethylene vinyl acetate (EVA) and hardening of the backsheet. The energy consumption measured at the laboratory scale corresponds to the optimum response value of 0.132 kWh, demonstrating the effectiveness of the study under short-term and stable conditions. The c-Si wafer analyzed using techniques such as EDXRF, XRD, TGA, FTIR, and SEM/EDS. 87.5% Si, 1.95% aluminum, 1.12% silver, and 1.23% other metals were recovered from the solar cell. However, an oxidation rate of 6.71% by mass was detected in the c-Si wafer. The recovery rate of valuable minerals by ignoring oxidation is 98.4% of the total mass.