Effects of Temperature and CSSX Organics on Saltstone Processing Properties

This task was performed to determine whether the two variables, ''mix temperature'' and ''quantity of organics'' introduced into the decontaminated salt solution by the caustic side solvent extraction (CSSX) process, need to be included in the upcoming Saltstone Variability Study. Because the amount and types of organics introduced through the CSSX process do not significantly impact the fresh properties of Saltstone, the ''quantity of organics'' variable will not be included in the Saltstone Variability Study. The Saltstone Variability Study should include the variable of ''mix temperature'' in the experimental design. Examples are presented in this report that clearly demonstrate a pronounced dependence of the fresh grout properties on ''mix temperature''. One example, using mixes made with the Deliquification, Dissolution and Adjustment (DDA) simulant, shows that the properties of gel time and bleed water are highly mix temperature dependent. The gel time increased from 15 minutes at 10 C to 90 minutes at 35 C with most of the change occurring between 20 and 30 C. That is, gel time is highly sensitive to mix temperature, especially in the temperature range over which processing is most likely. The volume percent bleed water for these mixes increased from ∼1 % at 10 C to 13 % at 35 C. The gel times and volume percent bleed water are correlated such that the longer the gel time, the greater the amount of bleed water. In another example, and in contrast to the DDA results, gel times decreased with increasing temperatures for mixes made using the Modular CSSX Unit (MCU) simulants. In this case the gel time decreased from 150 minutes at 10 C to 20 minutes at 38 C. The rheological properties of these mixes were shown to be dependent on temperature over the range of 10 to 40 C. The plastic viscosity increased from 35 cP at 40 C to values between 60 to 70 cP at 10 C for these mixes. Yield stress values for these mixes increased slightly with increasing temperature. The properties of yield stress and plastic viscosity are important parameters because they are related to pumping of these slurries through the pipeline to the vault and the flow of the grout in the vaults