Green and Efficient TBLS Process for Rare-Earth Element Recovery from Alkaline Rock-Carbonatite-Related Deposits

Rare-earth elements (REEs) play a critical role in modern life and industry; however, conventional extraction methods for REEs from alkaline rock-carbonatite deposits are often environmentally challenging and inefficient. In this study, we proposed a newly green and efficient process termed low-temperature thermal activation-noncontact bioleaching-biosorption (TBLS) for the recovery of REEs. The bioleaching procedure involves a two-step pretreatment of the ore with low-temperature thermal activation, followed by noncontact bioleaching using the metabolites secreted by Aspergillus niger (A. niger). Under optimized conditions, the TBLS process achieved an impressive REEs leaching efficiency of 84.51%, which is over 40 times more efficient than traditional bioleaching methods. Additionally, the separated cells of A. niger demonstrated exceptional adsorptive capability, effectively capturing more than 800 mg/L REEs. Moreover, the REEs extracted in the leachate were selectively recovered by A. niger, enabling the regeneration and recycling of the biolixiviant, thereby minimizing the environmental impact. The leaching residue was found to be nontoxic, and the cells could be reused for recovery of REEs from the leachate, further reducing environmental harm. Characterization results revealed that mineral structure activation (thermal decomposition) and metabolite effects (adsorption, dissolution, and complexation) were mainly involved in the TBLS process. This eco-friendly and high-efficiency approach presents a sustainable alternative to conventional REEs extraction methods.