Dissolution studies with pilot plant and actual INTEC calcines

Abstract

The dissolution of INTEC (previously the Idaho Chemical Processing Plant) pilot plant calcines was examined to determine solubility of calcine matrix components in acidic media. Two representative pilot plant calcine types were studied: Run 74 Zirconia calcine and Run 64 Zirconia/Sodium calcine. Dissolution of the calcines were evaluated using lower initial concentrations of nitric acid than used in previous tests to decrease the [H + ] concentration in the final solutions. Lower [H + ] concentrations contribute to more favorable TRUEX/SREX solvent extraction flowsheet performance. Experimental results indicated the following conditions define the baseline dissolution process for Zr calcine types:Under the above conditions, the final dissolved solutions contained an H + concentration of ~1.2 M while dissolving >95 wt. % of initial calcine mass. The solution stability adequately met previous calcine dissolution criteria.Dissolution and analytical results were also obtained for radioactive calcines produced in 1998 during NWCF campaign H-4. This calcine was produced using high sodium feeds from tanks WM-185 and WM-188 blended with non-radioactive Al(NO 3 ) 3 solutions to dilute the sodium concentration and prevent bed agglomeration during the calcination process. Due to the addition of Al(NO 3 ) 3 , the H-4 calcines composition resemble that of Al types. Dissolution tests indicated >95 wt. % of the initial calcine mass can be dissolved using the above baseline dissolution procedure, with the exception that higher (5.1 to 5.9 M HNO 3 ) initial nitric acid concentrations are required. The higher initial acid concentration is required for stoichiometric dissolution of the oxides, primarily aluminum oxide, Al 2 O 3 .Statistically designed experiments using Run 74 pilot plant calcine were performed to determine the effect of mixing rate on dissolution efficiency. Three variables were ranked using an interaction analysis to determine the effects of three process variables on the measured response (wt. % dissolution.) The variables were ranked in order of decreasing effect:Temperature > Acid/Calcine Ratio > Mixing Rate Mixing rate was determined to provide minimal effects on wt. % dissolution. The acid/calcine ratio and temperature were the predominate variables affecting the wt. % dissolution, a result consistent with previous studies using other similar types of pilot plant calcines.iv ACKNOWLEDGEMENTS