This work presents a water-based process for the manufacture of a polymeric waste form for the encapsulation of soluble toxic salts. The process is based on the elaboration of an aqueous emulsion in which polymeric precursors are mixed with the waste. Upon drying and curing, the emulsion inverts to form a waste form with mechanical integrity that stabilizes the toxic salt. The final polymer matrix is a mixture of an epoxy resin and poly(styrene butadiene) (PSB). Sodium nitrate was used as a model salt waste. The microstructure and composition of the samples were examined using scanning electron microscopy, osmium tetroxide staining, and salt extraction. The results show that the epoxy resin is dispersed in a continuous PSB phase, and the encapsulated salt is distributed throughout the matrix. Leaching tests were carried out by exposing sections of the waste forms to large volumes of well-stirred water. The measured time dependence of the leaching process is described quantitatively by a model based on the diffusion of the salt through the waste form. Effective diffusivities of the salt in the polymeric matrix ranged between 10-8 and 10-7 cm2/s. The results suggest that diffusion occurs through limited but significant continuous porosity.

This work explores the use of an aqueous-based emulsion process to create an epoxy/rubber matrix for separating and encapsulating waste components from salt-laden, arseniccontaminated, amorphous iron hydrate sludges. Such sludges are generated from conventional water purification precipitation/adsorption processes, used to convert aqueous brine streams to semi-solid waste streams, such as ion exchange/membrane separations, and from other precipitative heavy metal removal operations. In this study, epoxy resin and polystyrene butadiene (PSB) rubber emulsions are mixed together, combined with residual sludge, and cured and dried at 80°C to remove water. The microstructure of the resulting waste form is characterized by scanning electron microscopy (SEM), which confirms that the epoxy/PSB matrix surrounds and encapsulates the arsenic-laden amorphous iron hydrate phase, while allowing the salt to migrate to internal and external surfaces of the sample. Soluble salts leach from the sample at a rate given by diffusion coefficients of the order of 10 -8 cm 2 /s. Long-term leaching studies reveal no evidence of iron migration and, by inference, arsenic migration, and demonstrate that diffusivities of the unextracted salt yield leachability indices within regulations for non-hazardous landfill disposal.