Bacterially Produced Calcium Phosphate Nanobiominerals: Sorption Capacity, Site Preferences, and Stability of Captured Radionuclides

Abstract

A Serratia sp. bacterium manufactures amorphous calcium phosphate nanominerals (BHAP); this material has shown increased sorption capacity for divalent radionuclide capture. When heat-treated (≥450 °C) the cell biomass is removed and the biominerals are transformed to hydroxyapatite (HAP). Using a multimethod approach, we have elucidated both the site preferences and stability of analogue radionuclide incorporation for Sr, Co, Eu, and U. Strontium incorporates within the bulk amorphous inorganic phase of BHAP; however, once temperature modified to crystalline HAP, bonding was consistent with Sr substitution at the Ca(1) and/or Ca(2) sites. Cobalt incorporation occurs within the bulk inorganic amorphous phase of BHAP and within the amorphous grain boundaries of HAP. Europium (an analogue for trivalent actinides) substituted at the Ca(2) and/or the Ca(3) position of tricalcium phosphate, a known component of HAP grain boundaries. Uranium was surface complexed with no secondary minerals detected. With multiple sites for targeted radionuclide incorporation, high loadings, and good stability against remobilization, BHAP is shown to be a potential material for the remediation of aqueous radionuclide in groundwater.

Bio-Reclamation of Strategic and Energy Critical Metals from Secondary Resources

“…The interactions of REEs with biogenic phosphates and specific transporter uptake are two recently disclosed processes having the potential to recover the REEs from aqueous waste streams. Firstly, the sorption on, or the encapsulation into the biogenic phosphate nano-minerals and the formation of REE-phosphate complexes were demonstrated using biofilms of Serratia strains [37,38]. Using an extremophile, acidophilic methanotrophic Methylacidiphilum fumariolicum, Pol et al [39] observed that the function of methanol dehydrogenase (MDH) in this bacterium strictly depends on the presence of REEs.…”

Recovery of critical metals using biometallurgy

“…Firstly, the sorption on, encapsulation into biogenic phosphate nanominerals and formation of REE-phosphates were demonstrated using biofilms of Serratia strains [63,64]. The formation of biogenic Ce phosphates was also shown to occur on the Mn-oxidizing bacteria Leptothrix and Pseudomonas [65].…”

Uranium Bio-Transformations: Chemical or Biological Processes?

“…The mechanism of bio-mineralization has been well-characterized in the γ-Proteobacteria Serratia sp. [145]. Uranium is trapped on the surface of the cell or in the extracellular matrix on material like EPS, extracellular polymeric substances (Figure 2.1).…”

“…The surface-complexed uranium, phosphate and often calcium react forming immobilized minerals [81] [82] [145]. In Serratia this is seen under fermentative growth and different minerals may be produced under phosphate limited conditions [82].…”