Precipitation of metal hydroxides from aqueous solutions as a result of spontaneous condensation of polynuclear hydroxocomplexes
Вантажиться...
Дата
2021
Автори
Науковий керівник
Назва журналу
Номер ISSN
Назва тому
Видавець
КПІ ім. Ігоря Сікорського
Анотація
Background. Generally, it is assumed that the formation of a solid phase (precipitate) happens when the activities of the involved ions would exceed those defined by the thermodynamic solubility product. However, in case of precipitation of metal hydroxides, this is a simplification, and the real pattern is more complicated, since metal ions form strong mono- and polynuclear hydroxocomplexes in a solution. Formation of such complexes, especially those with zero charge, should result in the deviation from the common solubility product rule. Objective. The aim of this paper is to develop a precipitation model, which takes into account the effect of the for mation of the hydroxocomplexes on the solubility of a metal hydroxide. Eventually, this solubility includes the sum of the concentrations of metal ions, and all neutral, positively and negatively charged hydroxocomplexes involved in all equilibria in aqueous solution. Methods. We assume that formation of the solid precipitate is the result of spontaneous condensation of polynuclear neutral hydroxocomplexes when their concentrations in a solution exceed a certain critical value. These critical concentrations can be estimated from the consideration of all equilibria with the assumption that the equilibrium constants for the formation of neutral polynuclear complexes when their nuclearity increases by one are approximately equal and do not significantly depend on the size of the particle. Results. Using this approach, we developed the model, which predicts spontaneous condensation with formation of a precipitate. Also, we calculated the dependencies of pH-logCM for precipitation of various divalent cation hydroxides. It was shown that there exist minimal concentrations, below which no precipitates are formed at any pH value. Conclusions. Such approach also explains the nature of linear correlations between logarithms of solubility products and stability constants of neutral complexes described in literature. These results are important for the development and optimization of industrial wastewater treatment processes.
Опис
Ключові слова
solubility, metal hydroxides, metal hydroxocomplexes, розчинність, гідроксиди металу, гідроксокомплекси металів, растворимость, гидроксиды металлов, гидроксокомплексы металлов
Бібліографічний опис
Andriyko, Yu. Precipitation of metal hydroxides from aqueous solutions as a result of spontaneous condensation of polynuclear hydroxocomplexes / Yu. Andriyko, O. O. Andriiko // Наукові вісті КПІ : міжнародний науково-технічний журнал. – 2021. – № 1(132). – С. 76–82. – Бібліогр.: 13 назв.