Simultaneous Separation of Pd, Rh, and Ru from Simulated Radwaste Using Tin as the Solvent Metal prior to Final Vitrification into Borosilicate Glass: An Attempt to Recover Wealth from Waste

Abstract

Platinum group metals (PGMs), namely, Ru, Rh, and Pd, were removed simultaneously from molten borosilicate glass containing simulated high-level waste (HLW), using Sn as the solvent metal. The metal and glass phases were separated from each other after the melting was completed. The metal and glass phases were examined using X-ray diffraction and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis; the composition of alloy phase was analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). The percentage of recovery of the metal phase was 80%–87%. The metallic tin phase was found to contain PdSn4, Ru2Sn3, Ru3Sn7, and Pd0.15Rh0.15Ru0.70 intermetallic compounds, which crystallize in orthorhombic, tetragonal, cubic, and hexagonal structures, respectively. On dissolving the alloy in aqua regia, Ru3Sn7 and Pd0.15Rh0.15Ru0.70 were found to remain as an insoluble residue. The insoluble character of Ru3Sn7 and Pd0.15Rh0.15Ru0.70 affects the material balance of each element in the glass and metal alloy phases. The PGMs were separated to the metal alloy phase along with significant quantities of Fe, Te, Ni, and Mo, leaving behind Cs, Sr, and Zr in the glass phase. The recovery of PGMs has dual benefits; the removal of PGMs facilitates smooth vitrification of the waste by Joule heating. The other benefit is that of recycling PGMs (which are rare precious metals) from the waste.