Poly(acrylic acid) as a rheology modifier for dense alumina dispersions in high ionic strength environments

Rheological modifiers are currently being investigated for effective transport of dense radioactive nuclear waste slurries in the vitrification process developed for more permanent radioactive waste disposal. Recently, poly(acrylic acid) (PAA) was found to be a promising candidate for reducing the yield stress and viscosity of these waste slurries, of which aluminum hydroxides are a major component. This work focuses on dense alumina dispersions stored in an environment similar to that of the nuclear waste slurries, viz., strong basic conditions (0.5N NaOH) with high salt concentrations (0.1N–1N KNO3). It was found that the correct choice of molecular weight of the PAA was especially important to its effectiveness as a rheology modifier: too low a value provides insufficient steric stabilization, while too high a value induces bridging. Experiments are conducted to determine the effective molecular weight range for minimization of yield stress and viscosity and its dependence on ionic strength. An observed shift in the effective molecular weight range with salt concentration was attributed to changes in PAA conformation with ionic strength.