PNNL

Abstract

Controlling the stability and rheological properties of colloidal slurries has been an important but challenging issue for various applications such as cosmetics, ceramic processing, and nuclear waste treatment. For example, at the Department of Energy (DOE) Hanford and Savannah River sites, operation of the waste treatment facilities with increased solids loading affects waste processing rates but impacts the rheological properties. We investigated various rheological modifiers on a Fe2O3-rich nuclear waste simulant, characterized by high ionic strength and pH, in order to reduce rheological properties of the colloidal slurry. Rheological modifiers change particle interactions in colloidal slurries; they mainly alter the electrostatic and steric interactions between particles, leading to a change in rheological properties. Weak acid type rheological modifiers strengthen electrostatic repulsion whereas nonionic/polymer surfactant type rheological modifiers introduce a steric repulsion. Using rheological analysis, it was found that citric acid and polyacrylic acid are good rheological modifiers for the simulant tested, effectively reducing yield stresses by as much as 70%. Further analysis supports that addition of such rheological modifiers increases the stability of the slurry. Binding cations in bulk solution and adsorption on the surface of the particles are identified as a reasonable working mechanism for citric acid and polyacrylic acid.