Experimental results of calcine dissolution studies performed during FY-94,95

Calcine dissolution studies were performed in FY-94,95 in order to extend the knowledge of dissolution and to obtain information necessary for scale-up design and operation. Experiments reported in this document were performed with non-radioactive and actual calcines to generate qualitative data regarding: (a) calcine dissolution rates, (b) undissolved solids settling characteristics, (c) undissolved solids heel formation, and (d) chemical treatments for undissolved solids heel dissolution. The goal of this work was to achieve complete calcine dissolution, or to determine conditions that would result in the maximum calcine dissolution. Small scale laboratory experiments (test-tube dissolutions) and a bench scale dissolver set-up were used in the effort. Results from this work show the bulk of the undissolved solids to settle at a rate of >9 inches per second when the baseline dissolution parameters are used. Baseline dissolution parameters were 100 grams of calcine being dissolved in 1 L of 5 M HNO{sub 3} at > 90 C while the solution is being vigorously and constantly mixed. This work also verified that dissolution is most complete when performed with aggressive mixing. Sequential dissolutions performed with non-radioactive and actual calcine indicate that little undissolved solids heel build-up is expected, and this small heel can be further dissolved by increasing the dissolution time or by adding fresh nitric acid