Chemistry Seminar - Andrew Ansah, PhD Student

Title:

SYNTHESIS OF SYNTHETIC ROCK (SYNROC) IN ONE-STEP USING DIFFERENT METHODS.

Abstract:

The constituents in high-level waste generated from used nuclear fuel can be sequestered into synthetic rock (SYNROC). One major purpose of SYNROC is to prevent leaching of fission products and actinide elements into the environment. SYNROC is a multi-phase ceramic material and contains phases adopting the crystal structures of CaZrTi2O7 (zirconolite), CaTiO3 (perovskite), Ba1.2Al2.4Ti5.6O16 (hollandite) and TiO2 (rutile). SYNROC is considered to be a strong candidate for long-term immobilization of used nuclear fuel and it is one of the most effective alternatives to borosilicate glass waste forms for sequestering nuclear waste.

This presentation will discuss our efforts to synthesize SYNROC using one-step methods. ANSTO (Australian Nuclear Science and Technology Organisation) forms ANSTO SYNROC by mixing nuclear waste with the reactants required to form SYNROC in a single step to produce a granular powder for sintering using hot isostatic pressing and spark plasma sintering to fuse the waste form together. It has been confirmed based on previous studies that SYNROC can be formed in multiple steps and it would be beneficial to investigate if SYNROC can be successfully synthesized in one-step. The synthesis of SYNROC using a one-step method via the co-precipitation, sol-gel, and ceramic methods has not been studied in detail. The hypothesis is that SYNROC can be produced in one-step using the co-precipitation, sol-gel and ceramic methods. Another focus of this study was to reduce the reaction temperature when synthesizing SYNROC.

The SYNROC materials have been investigated by X-ray absorption near edge spectroscopy (XANES) and X-ray diffraction (XRD). XRD was employed to confirm the phase purity of the SYNROC materials. The wt% of the individual phases in the SYNROC materials were determined and compared to the expected values. Ti K-edge XANES spectra were collected from the SYNROC materials and the spectra were simulated based on the XRD results. The compositional values of CaZrTi2O7, Ba1.2Al2.4Ti5.6O16, CaTiO3 and TiO2 were fixed to simulate the Ti K-edge spectra from the SYNROC samples. Zr K-edge XANES spectra were collected to confirm that the only Zr-containing species in the synthesized SYNROC samples was zirconolite. The scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDX) maps and spectra of the SYNROC material revealed the distribution of elements throughout the material and confirmed the presence of all four expected phases. This study has demonstrated that SYNROC can be synthesized in one-step using the ceramic method, the co-precipitation method and the sol-gel method.

Date: Wednesday, July 17

Time: 1.30PM

Place: Thorvaldson 159