Abstract
Cerium has many modern applications such as in renewable energies and the biosynthesis of nanomaterials. In this research, natural struvite was solubilized by Aspergillus niger and the biomass-free struvite leachate was investigated for its ability to recover cerium. It was shown that struvite was completed solubilized following 2 weeks of fungal growth, which released inorganic phosphate (Pi) from the mineral by the production of oxalic acid. Scanning electron microscopy (SEM) showed that crystals with distinctive morphologies were formed in the natural struvite leachate after mixing with Ce3+. Energy-dispersive X-ray analysis (EDXA), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirmed the formation of cerium phosphate hydrate [Ce(PO4)·H2O] at lower Ce concentrations and a mixture of phosphate and cerium oxalate decahydrate [Ce2(C2O4)3·10H2O] at higher Ce concentrations. The formation of these biogenic Ce minerals leads to the removal of > 99% Ce from solution. Thermal decomposition experiments showed that the biogenic Ce phosphates could be transformed into a mixture of CePO4 and CeO2 (cerianite) after heat treatment at 1000 °C. These results provide a new perspective of the fungal biotransformation of soluble REE species using struvite leachate, and also indicate the potential of using the recovered REE as biomaterial precursors with possible applications in the biosynthesis of novel nanomaterials, elemental recycling and biorecovery.Key points• Cerium was recovered using a struvite leachate produced by A. niger.• Oxalic acid played a major role in struvite solubilization and Ce phosphate biorecovery.• Resulting nanoscale mineral products could serve as a precursor for Ce oxide synthesis.
Highlights
Cerium (Ce) is classified as one of the light rare earth elements (REE) in the lanthanide series and bears similar physical and chemical properties to lanthanum (Massari and Ruberti 2013)
After the sixth day of incubation, oxalic acid was detected in all liquid samples at concentrations of 9.18 ± 1.90 mM and 26.77 ± 0.04 mM for the natural struvite leachate and struvite-free culture, respectively (Fig. 2A)
The natural struvite sample contains a rich source of P, which was completely released after incubation with A. niger in liquid MCD medium
Summary
Cerium (Ce) is classified as one of the light rare earth elements (REE) in the lanthanide series and bears similar physical and chemical properties to lanthanum (Massari and Ruberti 2013). Cerium compounds are traditionally used in components of cigarette lighter flints, petroleum cracking catalysts, energy-efficient light sources and solid oxide fuel cells (SOFC) (Li et al 2000; van Krevel et al 2002; Martínez-Arias et al 2005; Haque et al 2014). Applied Microbiology and Biotechnology (2022) 106:821–833 nanoscale cerium compounds have been synthesized and new applications discovered in biomedical sciences such as bioimaging, biosensing and therapeutic nanomaterials (Babu et al 2010; Siposova et al 2019; Singh et al 2020). As more novel applications are emerging, cerium will be one of the most promising rare earth elements that deserves attention
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