Cast Stone Oxidation Front Evaluation: Preliminary Results For Samples Exposed To Moist Air

Technetium and Iodine Getters to Improve Cast Stone Performance

“…By comparison, only 0.015 and 0.167 meq are needed to reduce the Tc(VII) present in 100 mL for the C1 and C3 tests, respectively. The reduction capacity for BFS1 and BFS2, which was measured using the Ce(IV) methodology of Angus and Glasser (1985), was 0.793 and 0.800 meq/g [Um et al (2012[Um et al ( , 2013], and 0.884 and 0.725 meq/g [Langton et al (2013)], 2 respectively. Because only 1 g of getter material was used in the experiments conducted at a 1:100 getter-to-LAW simulant ratio, there was insufficient reduction capacity to reduce all of the Cr and Tc present in the LAW simulant.…”

“…The obvious implication of Oblath's (1984) and Langton's (1988) studies, and many more recent ones, is that the BFS has reduced the Cr(VI) and Tc(VI) species to their much more insoluble Cr(III) and Tc(IV) species. To quantify the reducing capacity of BFS, as well as the other two ingredients cement and fly ash, Roberts and Kaplan (2009), Kaplan et al (2008), Um et al (2012Um et al ( , 2013, and Langton and Almond (2013) measured the reductive capacity of the dry blend ingredients used in Cast Stone and Saltstone. They found that the BFS has a large reductive capacity (~790 to 820 μeq g -1 ) compared to Portland cement (198 μeq g -1 ) and fly ash (299 μeq g -1 ).…”

Technetium Immobilization Forms Literature Survey

“…In an electrochemical reduction process, liquid wastes are processed through electrochemical cells. In reduction mode, the Tc deposits on the cathode, presumably as Tc metal but perhaps also as TcO 2 (Lawrence et al 1997). The Tc would then be redissolved off the cathode into a dilute caustic or acid solution for storage or immobilization (McCabe et al 2012).…”

“…The electro-reduction process would also reduce other components in the wastes including nitrate, nitrite, and chromium. The electrochemical reduction process has been demonstrated at the laboratory scale on selected Hanford tank wastes (Lawrence et al 1997).…”

“…For smaller-sized reducing grout monoliths (because of their larger ratio of surface area to volume), oxygen diffusion into the waste form and reoxidation of Tc(IV) may be an issue that needs to be considered. Recently Langton and Almond (2013) performed experiments wherein the tops of reducing grout cylinders were exposed to moist air and then the grouts were sectioned into thin slices from top to bottom. The thin sections were leached in water for a short period to determine the depth at which reduced Cr and Tc were reoxidized-only oxidized Cr and Tc are expected to water leach.…”