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.
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