Wet chemical processing for nuclear waste glass to retrieve radionuclides

Here, we show unexpected and significant elution behavior of various elements from simulated nuclear waste glass (NWG) in ∼10° mol dm^-3 acidic solutions below 100 °C, where a borosilicate-based glass matrix has been believed to be chemically durable. Most elements like glass main components (Li, B, Na, Ca, Al, and Zn, but except for Si) and simulated radionuclides (Rb, Cs, Sr, Ba, Se, Te, Mn, Pd, Mo, rare earths, Cr, Fe, and Ni) were remarkably eluted from the simulated NWG in ∼10° M HNO₃ aq with Cl^- at 90 °C. Especially, the elution of Pd is governed by its coordination chemistry including a redox reaction, because Pd(0) present in the simulated NWG has to be oxidized to Pd²⁺ which forms [PdCl₄]^2- for its dissolution. While Zr in simulated NWG is sparingly eluted even in this treatment, its elution actually proceeds in 1-3 M H₂SO₄ aq at 90 °C thanks to strong coordination of Zr(IV) with SO₄^2-. Through design and optimization of the leaching conditions, a protocol of the wet chemical process to retrieve the radionuclides from simulated NWG has been proposed and demonstrated.