Kinetic Investigation of Bioleaching Kinetics of Valuable Metals in Boron Waste

This study utilized boron waste containing significant amounts of valuable metals as a secondary resource for metal recovery. Critical metals—lithium (Li), rubidium (Rb), and cesium (Cs)—identified in the boron waste were extracted via bioleaching using the fungus Aspergillus niger (A. niger). Biological methods such as bioleaching are considered low-cost and environmentally friendly, proving particularly effective for metal recovery from secondary resources due to their efficiency in processing low-grade materials. Under the optimal conditions—31 days of incubation in a growth medium using a shaking incubator at 30 °C and 125 rpm—A. niger achieved bioleaching efficiencies of 78.67 % for Li, 37.44 % for Rb, and 30.47 % for Cs.To identify the rate-controlling mechanisms during bioleaching, two kinetic models based on the Shrinking Core Model (SCM) were applied. The kinetic analysis revealed that the leaching of all three metals was primarily governed by surface chemical reactions rather than diffusion through a product layer, as indicated by higher correlation coefficients. The presence of two kinetic stages for Li suggests a transition from a slow initial phase, likely due to surface passivation, to a faster dissolution stage as the reaction progressed. The rate constants (k) for the chemical control model were 0.0019–0.0238 day⁻¹ for Li, 0.0042 day⁻¹ for Rb, and 0.0034 day⁻¹ for Cs, indicating that Li dissolved more rapidly and exhibited the highest reactivity among the studied alkali metals.