Evidence of technetium and iodine release from a sodalite-bearing ceramic waste form

Abstract

Sodalites have been proposed as a possible host of certain radioactive species, specifically 99 Tc and 129 I, which may be encapsulated into the cage structure of the mineral. To demonstrate the ability of this framework silicate mineral to encapsulate and immobilize 99 Tc and 129 I, single-pass flow-through (SPFT) tests were conducted on a sodalite-bearing multi-phase ceramic waste form produced through a steam reforming process. Two samples made using a steam reformer samples were produced using non-radioactive I and Re (as a surrogate for Tc), while a third sample was produced using actual radioactive tank waste containing Tc and added Re. One of the nonradioactive samples was produced with an engineering-scale steam reformer while the other nonradioactive sample and the radioactive sample were produced using a bench-scale steam reformer. For all three steam reformer products, the similar steady-state dilute-solution release rates for Re, I, and Tc at pH (25 °C) = 9 and 40 °C were measured. However, it was found that the Re, I, and Tc releases were equal or up to 4.5x higher compared to the release rates of the network-forming elements, Na, Al, and Si. The similar releases of Re and Tc in the SPFT test, and the similar time-dependent shapes of the release curves for samples containing I, suggest that Re, Tc, and I partition to the sodalite minerals during the steam reforming process.

Mineral assemblage transformation of a metakaolin-based waste form after geopolymer encapsulation

“…During this period of increased pH, Al is not released into solution to the same extent as Na and Si. This trend is not observed with the granular material, P1BG, where Na, Al, and Si are released concomitantly due to the absence of a spike in pHresulting from the excess NaOH release at short time periods[48]. Similar results were observed when comparing the BSRG and BSRM materials; however the results are not shown here.…”

“…Releases of Cs, Re, and I from the BSRM mineral products show a similar behavior, thus are not given here. The steady-state release rate of the P1BM material based on Si release is 3.4 ± 1.1 × 10 -4 g/m 2 d while for the BSRM material the value is 4.4 ± 1.6 × 10 -4 g/m 2 d. These results are slightly lower than the values calculated for the B1BG and BSRG materials [48].…”

“…Zn ---4.3 1.7 ± 0.2 × 10 -1 3.0 ± 0.4 × 10 -1 6.9 ± 6.3 × 10 -2 8.9 ± 1.3 × 10 -2 3.5.3 Single-Pass Flow-Through (SPFT) Test Figure 8 shows the results of the measured SPFT effluent pH for the P1BG and P1BM samples. The dissolution kinetics of the granular P1B sample has been the subject of another publication [48]. When comparing effluent pH values from the P1BG and P1BM samples, we note a marked increase in the pH for the early samples from the monolithic material where the P1BM maximum pH was 10.5 at a 10 mL/d flow rate.…”

“…A similar trend is observed when comparing results of the BSRG and BSRM materials. For the results given in this section, we focus on the results of the P1B samples because it has been shown that the dissolution kinetics of the P1B and BSR samples behave similarly [48,63]. [64].…”

“…Results from the granular materials, P1B and BSR, are given elsewhere [48]. A schematic apparatus of the SPFT system is presented in Figure 1.…”