Highly selective extraction of Pd from nuclear glass waste through the combination of ultrasound-assisted acid leaching and solid phase adsorption

Abstract

The extraction of long-lived radionuclides from nuclear glass waste (NGW) is a prerequisite for nuclear transmutation and resource recovery. However, this remains a great challenge due to the recognized extreme chemical stability of NGW. Here, we demonstrate an ultrasound-assisted wet chemical dissolution method for the efficient elution of radionuclides from NGW. Most elements, including glass major constituents and radionuclides, were significantly leached out from NGW in 1 mL H2O2/2 M HCl solution within 1 h at 35 °C and 270 W ultrasound, which is much milder than conventional glass dissolution methods such as corrosive HF digestion and molten alkali fusion. In particular, the leaching of insoluble palladium is controlled by its redox reactions and coordinating chemistry, where Pd0 in the NGW is oxidized to Pd2+ by H2O2, which in turn coordinates with Cl- to form soluble PdCl42-. Moreover, insoluble Zr species can be efficiently eluted in ultrasound-assisted low concentration H2SO4 solution by strong coordination with SO42-. As a bonus, the NGW is converted into high-value-added microporous silica after elution, and PdCl42- can be selectively extracted from the complex eluent by an imidazole-modified mesoporous silica, which was further calcined to obtain the PdO-loaded silica nanomaterials for the efficient catalysts of the reductive conversion of 4-nitrophenol to 4-aminophenol. Therefore, our results provide new avenues for the highly selective extraction of key radionuclides from NGW and offer the possibility of their nuclear transmutation and reuse in the future.