Secondary Waste Form Screening Test Results—THOR® Fluidized Bed Steam Reforming Product in a Geopolymer Matrix

Abstract

Executive SummaryScreening tests are being conducted to evaluate waste forms for immobilizing secondary liquid wastes from the Hanford Tank Waste Treatment and Immobilization Plant (WTP). Plans are underway to add a stabilization treatment unit to the Effluent Treatment Facility to provide the needed capacity for treating these wastes from WTP. The current baseline is to use a Cast Stone cementitious waste form to solidify the wastes. Through a literature survey, DuraLith alkali-aluminosilicate geopolymer, fluidized-bed steam reformation (FBSR) granular product encapsulated in a geopolymer matrix, and a Ceramicrete phosphatebonded ceramic were identified both as candidate waste forms and alternatives to the baseline. These waste forms have been shown to meet waste disposal acceptance criteria, including compressive strength and universal treatment standards for Resource Conservation and Recovery Act (RCRA) metals (as measured by the toxicity characteristic leaching procedure [TCLP]). Thus, these non-cementitious waste forms should also be acceptable for land disposal. Information is needed on all four waste forms with respect to their capability to minimize the release of technetium. Technetium is a radionuclide predicted to be in the secondary liquid wastes in small quantities, but the Integrated Disposal Facility (IDF) risk assessment analyses show that technetium, even at low mass, produces the largest contribution to the estimated IDF disposal impacts to groundwater.To support a final waste form down-selection, Pacific Northwest National Laboratory (PNNL) is conducting screening tests on the candidate waste forms to provide a basis for comparison. This report documents the screening test results on the FBSR granular product encapsulated in a geopolymer (GEO-7) matrix. Ultimately, either one or a few waste forms will be chosen in a down-selection process. The down-selected waste form(s) will be compliant with regulations and performance criteria and will lead to cost-effective disposal of the WTP secondary wastes. Later, more comprehensive and longer term performance testing will be conducted, following the guidance provided by the secondary waste form selection, development, and performance evaluation roadmap.Three draft test protocols (e.g., 1313, 1315, and 1316) being developed for the U.S. Environmental Protection Agency (EPA) were used to screen the encapsulated FBSR stabilization technologies. These EPA draft methods are a combination of static and semi-dynamic leach experiments that can be used to provide more detailed mechanistic information on material performance in comparison to the current standard leach methods, such as ANSI/ANS 16.1 and TCLP. The EPA draft Method 1313 is a static-leach test method where extraction experiments are conducted in dilute acid or base with deionized water (DIW) over a range of pHs at a fixed liquid-to-solid ratio. Instead of a dilute acid or base at a fixed liquid-to-solid ratio, draft Method 1316 uses DIW as the leachant for a range of liquid-to-solid ratios. The EPA...

Radionuclide Retention Mechanisms in Secondary Waste-Form Testing: Phase II

“…The slightly larger amount of Tc leached from the DuraLith in comparison to Cast Stone is consistent with the higher Tc diffusivity found in EPA 1315 tests conducted in Phase I (Pierce et al 2010). The observed larger cumulative concentrations of Re leached from the Geo-7 encapsulated FBSR chunks using the EPA 1314 method also agreed well with the Re diffusivity results found in the independent FBSR testing (Pires et al 2011). The stop-flow technique applied to both the Cast Stone and DuraLith EPA 1314 column tests suggests that Tc release from both Cast Stone and DuraLith is controlled by slow diffusion processes because there were larger Tc concentrations in effluents collected right after restarting the flow.…”

“…The observed high cumulative concentration values as functions of cumulative LS ratio value (time) agree well with the high EC and alkalinity concentrations found in the leachates. Higher Re leachate concentration could also be due to high initial Re concentration used in preparation of FBSR (258 µg/g) (Pires et al 2011) compared to initial Tc concentrations used in both Cast Stone (0.16 µg/g) and DuraLith waste forms (0.30 µg/g for Batch #1 and 0.23 µg/g for Batch #2) (Pierce et al 2010).…”

“…This binder formulation used fly ash instead of the heat-treated metakaolin clay, and test monoliths were prepared with an FBSR product waste loading of 65.2%. More details regarding those two samples can be found in Pires et al (2011). One of the FBSR monolith samples was crushed and used for this radionuclide retention task.…”

Secondary Waste Form Down-Selection Data Package—Fluidized Bed Steam Reforming Waste Form

“…The filtrate was collected in vials with minimal head space and submitted for chemical analyses. The results of the EPA 1316 test are listed in Table 6.6 for the major cations and Table 6.7 for the RCRA metals, iodine, and rhenium from the crushed FBSR granular product in GEO-7 binder (Pires et al 2011). The pH of the leachate solutions was between 12.5 and 12.8 for all three liquid-to-solid (L/S) ratios.…”

“…The measured concentrations of the major cations in the crushed FBSR monolith material (FBSR granular product in GEO-7 binder) leached at various pH solutions are shown in Table 6.4 (Pires et al 2011). The concentrations increased as the leach solution pH decreased (became more acidic).…”