The chemistry of uranium in borosilicate glasses

The effects of Ce(IV), Cr(VI), Mn(III), and Fe(III) as potential oxidising agents on the stability of the redox states of uranium were measured experimentally in a borosilicate melt composition at 1150 deg C and a variety of oxygen fugacities. Cr(VI) and Mn(III) will completely oxidise all U(V) in the melt, while Ce(IV) will oxidise the U(V) to a significant degree. The presence of iron in the borosilicate melt does not appreciably perturb the distribution of the redox states of the uranium from that established in melts containing just uranium as a multivalent element. The redox chemistry of uranium in glass melts containing other multivalent elements further constrains the optimum conditions necessary for the stable incorporation of uranium within the glass matrix for the immobilisation of nuclear waste. (author)