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

Abstract

Pertechnetate ion (99TcO4 -, 10-4 M) in alkaline solution is quantitatively reduced to hydrous TcO2 by thermolysis (65 °C, 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 valunit{0.050}{M}). Nitrilotriacetic acid (NTA), oxalic acid, and citric acid provide ≤ 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 H2, 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 99Tc in alkaline nuclear wastes, e.g., Hanford tank wastes.