Coprecipitation of barium and strontium nitrates in the course of crystallization from nitric acid solutions and simulated high-level PUREX process raffinate

Abstract

The formation of solid solutions of barium and strontium nitrates in the course of precipitation from solutions of HNO3, La(NO3)3, and their mixtures was proved by X-ray diffraction, chemical analysis, and IR spectroscopy. Solid solutions of Ba(NO3)2 and Sr(NO3)2 in the system with water are formed from saturated solutions at 25°С and molar ratio Ba(NO3)2: Sr(NO3)2 < 10. True coprecipitation in a wide composition range in HNO3 solutions is observed when the total nitrate ion concentration (ΣNO 3 - ) reaches approximately 5 M and higher values. In La(NO3)3 solutions, the coprecipitation occurs at ΣNO 3 - ≥ 6.5 M. In the process, the Sr(NO3)2 concentration does not decrease below its solubility level. A solid solution is formed from aqueous solution at ΣNO 3 - < 5 M in the region of Sr(NO3)2 concentrations below its solubility level, which suggests different mechanisms of cocrystallization from neutral and acid solutions. A crystallographic study of the precipitate obtained from a mixture solution containing simultaneously barium and strontium nitrates against the background of 1 M La(NO3)3 and 2 M HNO3 showed that the crystals were covered with a noncrystalline shell, apparently, with a layer of adsorbed HNO3 released in the course of crystallization. The IR spectrum of such precipitate contains a band characteristic of molecular HNO3 in nonaqueous media, which probably suggests the formation of an adduct.