Enrichment of Terbium(III) under synergistic effect of biosorption and biomineralization by Bacillus sp. DW015 and Sporosarcina pasteurii

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Abstract
Biosorption and biomineralization are commonly used for the immobilization of metal ions. Biosorption is commonly used as a green method to enrich rare earth ions from wastewater. However, little attention has been paid to the facilitating role of biomineralization in the enrichment of rare earth ions. In this study, a strain of Bacillus sp. DW015, isolated from ion adsorption type rare earth ores and a urease-producing strain Sporosarcina pasteurii were used to enrich rare earth elements (REEs) from an aqueous solution. The results indicate that biomineralization accelerates the enrichment of Terbium(III) compared to biosorption alone. Kinetic analysis suggests that the main mode of action of DW015 was biosorption, following pseudo-second-order kinetics ( R 2 = 0.998). The biomineralization of DW015 did not significantly contribute to the enrichment of Tb(III), whereas excessive biomineralization of S. pasteurii led to a decrease in the enrichment of Tb(III). A synergistic system of biosorption and biomineralization was established by combining the two bacteria, with the optimal mixed bacteria ( S. pasteurii :DW015) ratio being 1:19. This study provides fundamental support for the synergistic effect of biosorption and biomineralization and offers a new reference for future microbial-based enrichment methods. IMPORTANCE: A weak microbially induced calcium carbonate precipitation (MICP) promotes the enrichment of Tb(III) by bacteria, while a strong MICP leads to the release of Tb(III). However, existing explanations cannot elucidate these mechanisms. In this study, the morphology of the bioprecipitation and the degree of Tb(III) enrichment were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The data revealed that MICP could drive stable attachment of Tb(III) onto the cell surface, forming a Tb-CaCO 3 mixed solid phase. Excessive rapid rate of calcite generation could disrupt the Tb(III) adsorption equilibrium, leading to the release of Tb(III). Therefore, in order for Tb(III) to be stably embedded in calcite, it is necessary to have a sufficient number of adsorption sites on the bacteria and to regulate the rate of MICP. This study provides theoretical support for the process design of MICP for the enrichment of rare earth ions.

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