Release and retention of uranium during glass corrosion

In order to investigate the release and retention of uranium during glass corrosion, static leach tests were performed on a simulated waste glass doped with uranium in deionized water for up to 423 days. Observation and analysis of the alteration layer formed on glass surface were carried out by means of optical microscopy, scanning electron microscopy (SEM) and analytical electron microscopy. Elemental concentrations of leachate were determined by ICP atomic emission spectroscopy, atomic absorption spectrometry and kinetic phosphorescence analyzer (KPA) (for uranium). An analytical electron microscopy provided that fibrous phase were developed on the outer surface of the alteration layer, as secondary phase, which should be clay minerals such as nickel–nontronite, or nickel-rich chlorite. Absence of uranium and rare earth elements (REEs) in the fibrous minerals suggests that the release of uranium and REEs can be controlled by precipitation of hydroxides rather than uptake in clay minerals. Experimental results and thermodynamic calculations suggest that the uranium concentration in the leachate is controlled by solubility of uranyl hydroxides such as UO2(OH)2 (s).