Hydroxyapatite Biosynthesis by aSerratiasp. and Application of Nanoscale Bio-HA in the Recovery of Strontium and Europium

Biotechnology Processes for Scalable, Selective Rare Earth Element Recovery

“…It is important to note that XRD analysis examines bulk sample and reports on only those components that are crystalline (even if in minor amounts), while selected area electron diffraction analysis examines only very small spots within a sample. The broad peaks for bio-HA [74,78,79] suggest the material contains poorly crystalline or amorphous components, as confirmed by the analysis of its crystallinity (below).…”

“…The material deposited in the biofilm within the EPM (Figure 9A) and biofilm between the cells (Figure 9B and D) was confirmed to be hydroxyapatite using selected area X-ray diffraction and X-ray powder diffraction analysis (XRD) [78] and estimation of the bio-HA nanoparticle size by the XRD patterns under various incubation conditions gave an average of 20-25 nm [78,79] as compared to the ~40 nm made by batch-grown cells [75] and ~80 nm of commercial hydroxyapatite ( Table 2) [73].…”

“…In a subsequent study (daily dosing with mixtures of CaCl 2 , G2P and citrate at pH 7.0, 8.6 or 9.2: 8 days; all of the Ca 2+ was removed each day) a known mass of bio-HA was made onto a known mass of bacteria (to give 50% loading as HA); here, the Eu 3+ uptake reached ~42 mg/100 mg bio-HA or 0.84 mg mineral (i.e. 84% of the mineral mass) [78]. The HA-crystallite size was 21 ± 1.6 nm from materials made at pH 7 and 8.6 (pooled data) [79].…”

“…The biofilm component of the continuously pre-grown bacterial culture was retained for use in this study (column tests). The planktonic cells fraction (from the vessel outflow) was used in previous work [78,79]. Cells were from two independent cultures (I and II).…”

“…HA materials are polycrystalline with characteristic grain boundaries containing amorphous calcium phosphate species; the highly amorphous nature of bio-HA together with the high occurrence of organic materials (above) suggests that the occurrence of grain boundaries would be large but it is difficult to see how Eu 3+ was loaded to >80% of the HA mineral weight [78] unless most of the material comprised ultra-small crystallites with a high proportion of surface calcium phosphate groups as compared to buried ones. It would be possible to calculate this in homogeneous material of known crystallite size but the nature of bio-HA and dependence on the exact conditions of synthesis would make this calculation very difficult.…”