Speaker
Mrs
Nadezhda Mishina
(Russian Federation)
Description
Ba(NO3)2 precipitation is one of the limiting factors in HLW evaporation during NPP spent fuel reprocessing. The model was proposed in our previous work [1] for approximation of the Ba(NO3)2 and Sr(NO3)2 solubility in HNO3 solutions using the law of mass action. As a result the two linear areas where identified according to slope of the solubility on total nitrate ion concentra-tion in logarithmic scale and the existence of the adducts, containing 1-2 molecules HNO3 molecules with Ba(NO3)2 and 2 ones with Sr(NO3)2 were suggested. The Ba(NO3)2 solubility in neutral solutions of Sr(NO3)2 is higher, while in the presence of ammonium and sodium or RE nitrates the curve shape is also characterized by the minimum, indicating in all the cases on the effect of nitrate complexation. In Ba(NO3)2 KNO3 system the formation of the slightly soluble double salt Ba(NO3)2∙2KNO3 is observed.
The chemical analysis using 137Cs or Be(NO3)2 as a reference mark in the case of Ba(NO3)2 or Sr(NO3)2, respectively, was carried out to calculate the volume of mother liquor captured by the precipitate. The amount of excess NO3--ion was compared with the excess of H+-ion in relation to metal amount in the precipitate. Ba(NO3)2 and Sr(NO3)2 precipitates in the range from 0 to 5 mol/dm3 HNO3 contained only small permanent amount of excess, occluded by precipitate. In-creasing of HNO3 concentration in the liquor > 7 mol/dm3 HNO3 led to a sharp increase of acid con-tent in precipitates, indicating on the complex compound formation during crystallization. In the same area co-crystallization of Ba and Sr nitrates took place.
IR spectra [2] including differential ones confirm the presence of excess nitric acid and/or wa-ter in wet precipitates of barium and strontium nitrates and in their solid solutions precipitated at the high acidity or obtained by re-crystallization during their mixing in wet form.
X-ray diffraction patterns and chemical analysis [2] of individual and co-crystallized barium and strontium nitrates also indicated on the formation of (Ba,Sr)(NO3)2 solid solutions of three compositions at 4 mol/dm3 HNO3 and more in mother liquor, the composition depending on Sr to Ba ratio in the liquor at significant Sr(NO3)2 molar excess and typical solubility of the latter. The pattern of double salt Ba(NO3)2∙2KNO3 was indentified as well.
So, the formation of adducts of barium and strontium nitrates with nitric acid was qualitative-ly confirmed by different methods indicating on their metastable nature, resulting in possible dis-placement of nitric acid monohydrate from forming matrix into pores of crystals.
1. Mishina, N.E., Akhmatov, A.A., Zilberman, B.Ya., et al. Radiochemistry, 2010, vol. 52, Iss. 5, pp 523-529.
2. Mishina, N.E., Zilberman, B.Ya., Lumpov, A.A., et al. Radiochemistry, 2013, vol. 55, Iss. 2, pp (in printing).
Primary author
Mrs
Nadezhda Mishina
(Russian Federation)
Co-authors
Mr
Boris Zilberman
(Russian Federation)
Mr
Dmitry Ryabkov
(Russian Federation)
