Chromium leaching from a silicone foam-encapsulated mixed waste surrogate

This study assessed chromium leaching from silicone foam-encapsulated salt waste, using a surrogate formulated after Department of Energy complex mixed waste. Two commercial formulations of silicone foam (Wacker ELEKTROGUARD 2100 and General Electric RTV-664) were evaluated as a function of waste load (28-48 wt %). Chromium leaching was formulation specific and increased with increasing waste load as measured by the Toxicity Characteristic Leaching Procedure (TCLP). Chromium release followed transport controlled dissolution at all waste loads under TCLP (cut samples) and Accelerated Leach Test (ALT)(molded samples) conditions. Aqueous and surface complexation modeling was also used to describe reduced chromium effective diffusivity due to iron oxide addition. Comparison of modeling and measured diffusivities as a function of waste load demonstrated that the total available iron surface site concentration increased with increasing waste load, consistent with pore differences measured by image analysis. These results provide a basis for further work on modeling and engineering waste encapsulation using silicone foam.