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

M. A. Ivanov, Design Engineer, Centre for Industrial Technology Engineering, e-mail: iamivma@gmail.com
G. G. Bozhko, Associate Professor, Department of Non-Ferrous Metals and Gold, Candidate of Technical Sciences, e-mail: bojko06@mail.ru
A. S. Medvedev, Professor, Department of Non-Ferrous Metals and Gold, Doctor of Technical Sciences, e-mail: mas1941medvedev@yandex.ru
V. P. Tarasov, Head of Department, Department of Non-Ferrous Metals and Gold, Doctor of Technical Sciences, e-mail: vptar@misis.ru

This paper looks at the process of atmospheric hydrochloric acid leaching of raw and roasting kaolin clay, as well as the process of pressure hydrochloric acid leaching of raw kaolin clay. It also examines the phase transformations that take place in the high-silicon aluminium material – i.e. the kaolin clay from the Troshkovsky deposit – during roasting. Dehydration of aluminium minerals contained in kaolin clay is associated with the process of dehydration of montmorillonites without destroying their crystal lattices. At the same time the kaolinites, which are poorly soluble in hydrochloric acid, acquire an acid-soluble form (amorphous aluminium silicate – metakaolinite). Optimum process conditions for kaolin clay roasting have been identified. A direct relationship has been established between the kaolin clay dehydration rate and the roasting temperature and time. It was found that the recovery of aluminium from roasting kaolin clay is more than three times higher than from raw kaolin clay if the process of atmospheric hydrochloric acid leaching is conducted in the same conditions. Optimum process conditions have been established for atmospheric and pressure hydrochloric acid leaching of kaolin clays, i.e. hydrochloric acid concentration, temperature and time. The activation energy has been determined for the process of pressure hydrochloric acid leaching of kaolin clay: E_act = 33 kJ/mol. The activation energy was calculated based on experimental data and it indicates that the process of pressure hydrochloric acid leaching of kaolin clay is constrained by theleaching agent diffusing to the reaction surface through a growing layer of the reaction products.

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