Empress Catherine the Great Saint Petersburg Mining University, Saint Petersburg, Russia

Т. Е. Litvinova, Professor of the Department of General and Physical Chemistry, Doctor of Technical Sciences, Professor, e-mail: litwinowa@spmi.ru
V. V. Vasiliev, Associate Professor of the Department of Metallurgy, Candidate of Technical Sciences, Associate Professor, e-mail: Vasilev_VV@pers.spmi.ru
N. V. Tuleshov, Postgraduate Student of the Department of General and Physical Chemistry, e-mail: nickolai.tuleshov@yandex.ru

The present study is devoted to the influence of dissolved sulfur in the form of sodium sulfate on the seeded precipitation of aluminum hydroxide from alkaline aluminate solutions. Experiments were performed with model slurries at varying sulfur content in terms of [SO₄^2–] from 0 to 18 g/l and the following initial parameters: [Al₂O₃] = 30.15 g/l, L_k = 1.67, seed ratio = 1.25. It was found that on the background of low seed ratio the presence of sulfate anion significantly stabilizes the solution, reducing decomposition rate proportional to the content of the impurity. For further analysis of the experimental data, we applied a mathematical model of gibbsite particles growth based on the hypothesis of uniform deposition of dissolved aluminate ions on the seed surface. Microstructural studies of the obtained precipitate confirmed the hypothesis about the predominantly spherical shape of the growing hydrate particles and reflected the uniform growth of the precipitate under the selected experimental conditions: high supersaturation of the model slurries in dissolved aluminum relative to the equilibrium values calculated by Rosenberg-Healy, as well as a reduced seed ratio. The convergence of measured and calculated values of specific surfaces of precipitates at the end of experiments was confirmed. According to the calculation results, under the experimental conditions, the initial effective rate of the decomposition process decreases linearly in proportion to the presence of sulfate in the range of 0 to 18 g/l, and further decrease of the effective rate with time does not depend on the impurity content. The work contributes to the understanding of the influence of sulfate on the rate of aluminum hydroxide precipitation and offers quantitative relationships to describe the process.

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