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 mixe d waste. Two commercial formulations of silicone foam (Wacker ELEKTROGUARD 2100 and General Electric RTV-664) were evaluated as a function of waste lo ad (28-48 wt %). Chromium leaching was formulation specific and increased w ith increasing waste load as measured by the Toxicity Characteristic Leachi ng Procedure (TCLP). Chromium release followed transport controlled dissolu tion at all waste loads under TCLP (cut samples) and Accelerated Leach Test (ALT) (molded samples) conditions. Aqueous and surface complexation modeli ng 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 po re differences measured by image analysis. These results provide a basis fo r further work on modeling and engineering waste encapsulation using silico ne foam.