SYNTHESIS OF VARIOUS APATITE AND APPLICATION FOR URANIUM REMOVAL

High-efficiency technology for the treatment and removal of radionuclides is required for radioactive remediation after nuclear accidents. In this study, different types of hydroxyl apatite (HA) using organic or inorganic phosphorus source were synthesized and used for uranium (U) removal under various conditions.

General HA, Ca₁₀(PO₄)₆(OH)₂ was synthesized by a solution-precipitation method. Tin-apatite was developed by substituting Ca²⁺ in the synthesized HA with Sn²⁺. Tributyl phosphate (TBP)-coated apatite (TBP-HA) was synthesized using TBP as organic phosphorus source. Because of the high stability constants of the actinide-organic phosphorus complexes, TBP has been widely used as one of the most favorable extractants for U in the nuclear engineering. TBP-HA was prepared at different pHs (pH=4, 7, 10), but synthesis was the most successful at neutral pH condition. In addition, organo HA was synthesized using the organic phosphate source from TBP or Trimethyl phosphate (TMP). Solid characterizations of various types of synthesized apatites were conducted by X-Ray Diffraction (XRD), ³¹P Nuclear Magnetic resonance (³¹P NMR), and Fourier transform infrared spectroscopy (FTIR). Using the various apatites, U removal was evaluated under different reaction times (1min, 1 hour, 1day, and 1week), aqueous solution (deionized water(DIW), 0.001 M NaHCO₃ and 0.1 M NaHCO₃), and U concentration (10 ppb, 100 ppb and 1000 ppb). After the reaction, the remaining U concentration was measured by Inductively Coupled Plasma Mass Spectrometer (ICP-MS).

Through various solid analyses, HA was successfully synthesized with different phosphorus sources. Uranium removal was almost 100% within 1 day of reaction by most of the HA materials when low carbonate background solutions (DIW and 0.001 M NaHCO₃) were used. However, uranium removal (%) decreased as NaHCO₃ concentration increased from 0.001 M to 0.1 M, because of U-carbonate aqueous complex formation. General HA showed better U removal than Sn-HA in DI and 0.001 M NaHCO₃ solution. Organo apatites prepared with TBP or TMP also showed high efficiency for U removal. The results provide insight into the potential for U removal using various types of apatites.