Characterization and Correlation of Particle-Level Interactions to the Macroscopic Rheology of Powders, Granular Slurries, and Colloidal Suspensions

Abstract

Executive SummaryHanford TRU tank sludges are complex mixtures of undissolved minerals and salt solids in an aqueous phase of high ionic strength. They show complex rheological behavior resulting from interactions at the macroscopic level, such as interparticle friction between grains in the coarse fraction, as well as from interactions at the nano-scale level, such as the agglomeration of colloidal particles. An understanding of phenomena such as interparticle friction and aggregate stability under shear will allow better control of Hanford TRU tank sludges being processed for disposal.The project described in this report had two objectives. The first was to understand the physical properties and behavior of the Hanford transuranic (TRU) tank sludges under conditions that might exist during retrieval, treatment, packaging, and transportation for disposal at the Waste Isolation Pilot Plant (WIPP). The second objective was to develop a fundamental understanding of sludge physical properties by correlating the macroscopic behavior with interactions occurring at the particle/colloidal scale. These objectives were accomplished by: 1) measuring the physical and rheology properties of actual Hanford tank samples, 2) developing continuum models for coarse granular slurries, and 3) studying the behavior of colloidal agglomerates under shear and under ion irradiation.The shear strength of coarse granular powders and slurries was studied to determine ways of characterizing (quantifying) the effect of interparticle friction and cohesion on incipient motion. Additional studies were performed to develop and validate a continuum model for cohesionless granular powders and slurries undergoing three-dimensional shear. With regard to incipient motion in dense slurries, the immersion depth and containing vessel diameter significantly impact shear strength . A model accounting for the effects of interparticle friction, slurry cohesion, vane size and immersion depth, and container geometry was derived using a saturating vertical stress profile. This model was able to adequately explain experimental observations with regards to variations in container size and vane immersion depth. The functional form of the Janssen formula provides a potential scaling relationship to apply small-scale shear vane results to engineering-scale applications dealing with coarse-grained slurry systems.For granular systems undergoing three-dimensional flow, a constitutive model was developed to describe flows of cohesionless granular solids. The model is based on the postulate that the friction coefficient and the solids fraction in a moving granular material are exclusive functions of an inertial number, which represents the ratio of inertial to normal stress forces. The constitutive equation obtained has the same form as a multidimensional Bingham fluid model, albeit with an apparent viscosity and yield stress that depend on the vertical normal stress distribution. The model was applied to previously published experimental results dealing with three-dim...