Ureolytic Nocardia tenerifensis-driven carbonate precipitation for enhanced La3+ adsorption and immobilization

Rare earth elements (REEs) are essential in numerous modern industries, yet their extraction presents significant environmental challenges. Sustainable recycling technologies for REEs are therefore crucial for both environment protection and resource conservation. Microbially induced calcite precipitation (MICP) offers a promising solution. This study focused on a high urease activity (216.5 U/mL), lanthanum-tolerant (400 mg/L) strain, Nocardia tenerifensis KLBMP 9777. Ca²⁺ addition during the MICP process significantly alleviated the La³⁺ toxicity and enhanced mineralization. The maximum removal rate of La³⁺ increased from 66.2% to 89.1%, while the urease activity also increased from 80.7 U/mL to 101.7 U/mL. Scanning electron microscope (SEM) and X-ray energy dispersive spectroscopy (EDS) revealed the formation of needle-like and rhombic crystal structures after mineralization. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) identified carboxyl, amino, carbonyl, and carbonate groups as key players in the MICP-mediated La³⁺ adsorption. Further analysis by X-ray diffraction (XRD), Transmission electron microscopy (TEM), and Thermogravimetry-derivative thermogravimetry analyses (TG/DTG) confirmed that the mineral deposits on the cell surface were calkinsite (La₂(CO₃)₃·4H₂O) and calcite (CaCO₃). The findings advance our understanding of the MICP mechanism and provide a theoretical foundation for its application in REEs recovery and environmental remediation.