National University of Science and Technology MISiS, Moscow, Russia:

V. I. Pak, Postgraduate Student, Department of Non-Ferrous Metals and Gold, e-mail: pak_vyacheslav@mail.ru
S. S. Kirov, Associate Professor, Department of Non-Ferrous Metals and Gold, Candidate of Technical Sciences, e-mail: kirovss@list.ru

O. I. Mamzurina, Senior Lecturer, Department of Non-Ferrous Metals Science, e-mail: mamzur309@mail.ru
A. Yu. Nalivaiko, Senior Lecturer, Department of Non-Ferrous Metals and Gold, Candidate of Technical Sciences, e-mail: nalivaiko@misis.ru

This paper examines how temperature, the concentration of AlCl₃ in the initial solution and the consumption rate of gaseous HCl impacts the degree of AlCl₃·6H₂O crystallization from aluminium chloride solutions resultant from leaching of Russian kaolin clays. The experiments involved introduction in the solution of return gaseous hydrogen chloride. This technique is based on decreasing the solubility of aluminium chloride while increasing the concentration of HCl in the system. The effect of impurity iron on the crystallization parameters has been studied. The initial solutions used in the experiments had the concentrations of iron chloride of 8.5 and 16.7 g/l. It was found that impurity iron does not produce any significant impact on the crystallization process. At the same time, a double increase of [Fe³⁺] in the initial solution leads to a 1.5-time increase in the iron concentration in aluminum chloride hexahydrate crystals. The findings show that the impurities contained in AlCl₃·6H₂O crystals mainly include residual mother solution on the particle surface. The effect of temperature has been established on the physical and chemical properties of deposited crystals. The average size of crystals produced during high-temperature AlCl₃·6H₂O crystallization was 500 μm, and it was 250 μm following low-temperature crystallization. The authors found that during high-temperature crystallization the AlCl₃·6H₂O particles form coarser agglomerates making crystal filtering and washing more efficient. Studies have been conducted with AlCl₃·6H₂O crystals produced in different crystallization regimes. The effect of using concentrated hydrochloric acid to wash AlCl₃·6H₂O crystals has been studied. It was found that due to crystal washing the amount of impurities carried away with the solution can be reduced by 70–80 %.

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