Stabilization of arsenic-bearing iron hydroxide solid wastes in polymeric matrices

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, arsenic-contaminated, 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 teachability indices within regulations for non-hazardous landfill disposal.