Solution interaction of nuclear waste anions with selected geological materials

Experiments with a wide variety of minerals have shown that a number of minerals will retard the movement of the radioactive waste anions SeO4/sup =/, TcO4- and I-. The SeO4/sup =/ anion is retarded by the greatest variety of materials which includes a number of silicates, sulfides and oxides. This retardation and the presence of 79Se in the waste in relatively low quantity implies that it does not represent a hazard, as similar or greater retardation is expected for the more reduced selenium species. The TcO4- and I- anions are more difficult to retard. However, studies have shown that a number of geological materials will retard TcO4- under oxidizing conditions. Research is in progress on the geochemical behavior of TcO4- and I- in reducing systems, and preliminary indications show that TcO4- will precipitate as an oxide. The retardation of I- is the more difficult, but investigations have shown that a number of minerals will retard its movement. Two lead minerals and Cu-metal have been shown to retard I- or at least minimize its solubility. The PbO-system sorbs I- from very dilute solutions. However, it remains to be shown that this material would be stable under repository conditions