Catalytic reduction of pertechnetate (99TcO4-) in simulated alkaline nuclear wastes

Pertechnetate ion ((TcO4-)-Tc-99, 10(-4) M) in alkaline solution is quantitatively reduced to hydrous TcO2 by thermolysis (65 degreesC, 4 days) in the presence of organic complexants and fission-product noble metals (RuCl3, RhCl3, and PdCl2; 0.001 M). Over 99% reduction occurs in the presence of ethylenediaminetetraacetic acid (EDTA), hydroxyethyl(ethylenediaminetriacetic acid) (HEDTA), or glycolic acid (0.050 M). Nitrilotriacetic acid (NTA), oxalic acid, and citric acid provide less than or equal to 2% reduction. Ruthenium, rhodium, and palladium chlorides also catalyze the reduction of TcO4- by hydrogen gas. The results are consistent with a two-step process of complexant degradation to generate H-2, followed by catalytic reduction of pertechnetate to hydrous TcO2 or soluble technetium complexes. Catalytic reduction is a viable, non-radiolytic route to the formation of non-pertechnetate species of Tc-99 in alkaline nuclear wastes, e.g., Hanford tank wastes.