Boehmite Dissolution Model Based on Simulant Data

Several of the Hanford waste tanks contain significant quantities of boehmite. This boehmite will be dissolved through caustic leaching as part of the Hanford Tank Waste Treatment and Immobilization Plant (WTP) currently under construction. Therefore, it is important to fully understand the nature of this dissolution process so that caustic leaching can be effectively deployed on the Hanford tank wastes. This research determined the impact of aluminate ion on the dissolution kinetics of boehmite. In addition, other parameters that impact boehmite dissolution, such reaction temperature, were also assessed and used to develop a semiempirical model of the boehmite dissolution process. A shrinking core model was used to fit data from a series of boehmite dissolution tests with an additional term added to account for the approach to saturation. This revised model provided an adequate fit to the experimental data; however, a superior fit to the experimental data was obtained when a term was added to represent the number of dissolution sites available at the start of the reaction. These results suggest that boehmite will dissolve significantly slower as gibbsite dissolves and adds aluminate to the solution. Practically, these results indicate that the blending of wastes with gibbsite and boehmite will ultimately result in either more caustic or more time required to achieve the same fraction of boehmite dissolution.