The rheology of colloidal suspensions can vary enormously depending on the contents of the suspensions and the details of how they were produced. Certain interactions between particles within colloidal suspensions can greatly affect their rheology which can be a serious impediment to their processing. For example, at DOE's Hanford site, the radioactive tank wastes are very concentrated and have formed a sludge that is too viscous to process. We are interested in understanding the rheology of this system in order to develop an efficient method for processing the waste. Towards this end we have developed a model silica system for the tank wastes whose particles can interact through chemical bonding, Keesom interactions, and Coulombic interactions. Through systematic variation of the solvent and the particle concentration we can alter the rheological behavior from shear thickening to shear thinning to Newtonian. We present preliminary results for this system as it applies to the processing of the tank waste at Hanford.