Recovery of Se, Zr, Pd, and Cs from simulated high-level radioactive waste glass through phase separation

Abstract

In this study, elemental recovery was performed using phase separation from simulated high-level radioactive waste (HLW) glass. To cause phase separation, SiO₂ and B₂O₃ were added to the simulated HLW glass and adjusted the ratio of SiO₂: B₂O₃: other oxides to 40:50:10. The phase separated glass was immersed in aqueous solutions of 0–3 mol/L of HNO₃, H₂SO₄, and a 1:1 mixture of HCl–HNO₃ at 363 K for 20 h, and the dissolution behavior of 17 elements was examined. The relationship between the dissolved mass fraction of each element and the acid concentration in the immersion liquid could be approximated by the modified sigmoid function. The recovery of stable nuclei Se, Zr, Pd, and Cs instead of long-lived radioactive nuclei was tested using a four-stage leaching process in which the sample was immersed sequentially in four aqueous solutions at 363 K of distilled water, HNO₃, H₂SO₄, and a 1:1 mixture of HCl–HNO₃ for 20 h. It was confirmed that Se, Zr, Pd, and Cs could be recovered selectively. Furthermore, the recovery result could be predicted based on the individual dissolution results described above.