The Bureau of Mines is investigating a method to dewater fine- particle clay waste. In order to more fully understand the effect of ion exchange on clay dewatering, an investigation of the rheological properties of ion-exchanged montmorillonite was undertaken. Viscosity measurements were made on ion-exchanged montmorillonite slurries of the following cations: na+, li+, nh4+, ca2+, mg2+, and la3+. The univalent ion-exchanged clays were found to have significantly higher viscosities than the multivalent exchanged clays. The measured viscosities were separated into Newtonian and non-Newtonian components using the ree-eyring equation. The magnitude of the Newtonian and non-Newtonian viscosity components was found to be dependent upon the floc volume, a parameter controlled by the degree of particle interaction, and the thickness of the individual montmorillonite platelets (tactoids). Both the tactoid thickness and the degree of particle interaction are determined by the hydrated-radius-to-charge ratio of the exchange ion. Research at the Tuscaloosa Research Center is carried out under a memorandum of agreement between the Bureau of Mines, U.S. Department of the Interior, and University of Alabama.