Cerium is a critical element to modern technologies. Nowadays, its increased applications have led to elevated levels in the environment. Cerium recovery by microorganisms has gained a great deal of attention. Here, our research showed that Bacillus licheniformis could be used to recover Ce3+ from aqueous solution. The adsorption capacity of cerium on this bacterial strain achieved 38.93 mg/g (dry weight) biomass. Adsorption kinetics followed a pseudo-second-order rate model, and adsorption isotherm was fitted well with the Freundlich model. Scanning electron microscope (SEM) observations coupled with X-ray energy dispersive spectroscopy (EDS) analysis revealed a spatial association of Ce with C, N, O, S, and P. Fourier transform infrared spectroscopy (FT-IR) analysis further suggested that the phosphate and carboxyl groups on the cell surface might be responsible for the adsorption of cerium. Furthermore, X-ray diffraction (XRD) and transmission electron microscopy (TEM) with electron energy loss spectroscopy (EELS) suggested that cerium initially occurred on the bacterial cell surface as Ce(OH)3, which was mainly converted to monazite (CePO4) and a small amount of CeO2 overtime. Hydrothermal treatment was used to accelerate the mineralization process of cerium by B. licheniformis. The hydrothermal treatment is conducted for comparative analysis of mineralization process in extreme geological condition.
Keywords: Biomineralization; Biosorption; Cerium; Microorganism; Rare earth element (REE).
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