Microstructure and leaching behavior of polymer composites for encapsulating toxic solid wastes

Abstract

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.