Washington River Protection Solutions is considering the design and construction of a Solidification Treatment Unit (STU) for the Effluent Treatment Facility (ETF) at the Hanford Site. The ETF is a Resource Conservation and Recovery Act-permitted, multi-waste, treatment and storage unit that can accept dangerous, low-level, and mixed wastewaters for treatment. The STU needs to be operational by 2018 to receive secondary liquid wastes generated during operation of the Hanford Tank Waste Treatment and Immobilization Plant (WTP). The STU will provide the additional capacity needed for ETF to process the increased volume of secondary wastes expected to be produced by the WTP. Pacific Northwest National Laboratory is conducting a secondary waste form screening program to support the evaluation and selection of waste forms to stabilize and solidify the liquid secondary waste stream from the WTP. The following monolith waste forms are being evaluated for immobilizing the secondary wastes: 1) Cast Stone; 2) DuraLith alkali aluminosilicate geopolymer; 3) Ceramicrete phosphate-bonded ceramic; and 4) THOR ® fluidized bed steam reforming waste product encapsulated in geopolymer. This report documents work to further develop and characterize the Cast Stone waste form. Other reports will cover the development and characterization of the other three waste forms. Follow-on activities will address the mechanisms of radionuclide retention to support disposal-system performance assessments, and regulatory and waste acceptance testing to demonstrate the waste forms will meet requirements for disposal at the Hanford Integrated Disposal Facility. Cast Stone (also called-Containerized Cast Stone‖) is a cementitious waste form that is essentially a mixture of Class F fly ash, Grade 100 or 120 blast furnace slag, and Type I/II Portland cement. CH2M Hill Hanford Group Inc. developed this waste form to solidify numerous waste streams, including secondary waste generated at the Hanford Site. The Cast Stone cementitious waste form is the current baseline for solidifying the liquid secondary wastes from the WTP. Pierce et al. (2010) demonstrated that the Cast Stone is a viable waste form for immobilizing WTP secondary wastes. This statement is based on the leachability of technetium-99 (99 Tc) as determined using draft U.S. Environmental Protection Agency (EPA) test methods examining contaminant diffusivity (Method 1315) and the impacts of solution pH (Method 1313) and liquid-to-solids ratio (Method 1316). 1 The Cast Stone testing reported here focused on optimizing waste loading and evaluating the robustness of the waste form to waste stream variability. Because of the extensive work on the Cast Stone formulation and the similar Saltstone formulation used at the Savannah River Site for low-level tank waste immobilization, testing conducted as part of this current test plan relied on those previous testing studies and did not aim to optimize the dry-blend material components or mix ratios beyond what has already been accomplished.

No abstract

v compared to the uncarbonated Cast Stone. Slightly increased porosity, ranging from 8.6% to 10.7% after carbonation using gas absorption analysis, also was measured in the weathered Cast Stone. A similar increased porosity was found in Cast Stone after carbonation (14 days) using the XMT analysis. However, smaller values of porosity were measured by XMT in Cast Stone before and after carbonation (14 days) because of the limited capability of the XMT technique to separate water-filled pore areas from cement solid materials-that is, the XMT was delineating mostly the small volume of air-filled pores and not the total porosity. The EPA 1314 method (up-flow percolation column leaching test) was used for the Cast Stone and DuraLith geopolymer (Batch #2) waste forms available from Phase I and for the Geo-7 encapsulated FBSR product recently available from Savannah River National Laboratory. The Tc concentrations leached from the DuraLith geopolymer packed column were slightly higher than the Tc concentrations leached from the Cast Stone packed column. Significantly higher Re concentrations were found in the leachates from the FBSR packed column. The stop-flow technique was also applied to the Cast Stone and DuraLith geopolymer packed columns. When the first effluents were obtained after flow was resumed, the Tc concentrations were significantly higher, which confirms that Tc releases from both Cast Stone and DuraLith were controlled by diffusion processes. Leachate concentrations for RCRA-listed metals from the packed columns were very low, a result that was similar for the Cast Stone and DuraLith waste forms. That is, none of the RCRA-listed metals present in the secondary waste simulants leached out of the Cast Stone or DuraLith in significant concentrations. Concentrations of RCRA-listed metals and major cations (including Re), electrical conductivity, and alkalinity were higher in the effluents from the packed column with FBSR encapsulated with Geo-7 monolith chunks using the EPA 1314 method. These high concentrations may be attributable to the higher concentrations of RCRA metals in the FBSR product that, after encapsulation in Geo-7, was used for the packed column test. EPA 1315 leach tests for Cast Stone and DuraLith monoliths from the Phase-I project were extended beyond 63 days to 90 days. The leach test results showed that the Tc diffusivity for the DuraLith Batch #1 and Batch #2 waste forms at 90 days were a bit higher than that observed for the Cast Stone. There also was a minor decreasing Tc diffusivity trend for the Cast Stone over the entire 90-day leaching period. The decreasing Tc diffusivity trend might be caused by ongoing carbonation reactions-that is, formation of calcium carbonate on the surface and within near-surface micro cracks that might be reducing the porosity of the monolith during the leach testing. The slightly increased Tc diffusivity in the DuraLith waste form near the 90-day leach interval might result from more dissolution of the DuraLith matrix with extended contact with the soluti...

No abstract

No abstract