Detecting and minimizing interferences in uranium oxidation states during dissolution of solid phases

Interferences in uranium oxidation states due to iron during acid dissolution of solid samples were studied. Hydrazine and different carboxylic acids were investigated for their suitability to minimize these interferences. Polyacrylic acid (PAA) was selected for further testing with common iron-containing minerals, pyrite and biotite. The interfering effect of iron decreased with increasing PAA concentration; 2.5% acid concentration was observed to be a suitable level to minimize interferences due to the iron-containing minerals. PAA and polyacrylic-co-maleic acid (PAMA) were tested for their effect on goethite. The oxidation of uranium by goethite was not supressed with the acids but further a slight oxidation was observed. Further experiments are required to find a suitable redox buffer for goethite and iron minerals. However, the promising results for pyrite and biotite widen the range of solid materials that can be considered suitable for the determination of uranium oxidation states. (author)