Bacterial acidic agents-assisted multi-elemental (Ni, Co, and Li) leaching of used lithium-ion batteries at high pulp densities

Accumulating used lithium-ion battery cathodes and associated environmental concerns necessitate efficient recycling strategies. This study introduces a breakthrough spent-medium bioleaching approach optimized for high-pulp-density conditions to address key challenges related to bacterial inhibition and sulfur availability for bacterial acidic agent production. Using response surface methodology, we optimized key variables including sulfur dosage, inoculum size, and initial pH, resulting in an optimized sulfate concentration of 40.3 g/l and a ΔpH of 1.87. We evaluated metal removal efficiency at pulp densities of 10–50 g/l, achieving significant extraction rates of lithium (92%), nickel (88%), and cobalt (78%) at the highest density of 50 g/l after 7 days of processing. A comparative analysis with traditional chemical leaching methods confirmed the effectiveness and sustainability of our green bioleaching strategy. Furthermore, a kinetic study utilizing the Avrami equation and the shrinking core model established that diffusion through the product layer was the controlling factor for the leaching rate. This research presents a comprehensive and sustainable strategy for the recycling of used lithium-ion batteries at high pulp densities by integrating process optimization, spent-medium bioleaching, and kinetic modeling for critical metal extraction.