National University of Science and Technology “MISiS”, Moscow, Russia:
S. S. Kirov, Assistant Professor of a Chair of Non-Ferrous Metals and Gold, e-mail: kirovss@list.ru
R. T. Khayrullina, Assistant Professor of a Chair of Non-Ferrous Metals and Gold
P. V. Aleksandrov, Assistant Professor of a Chair of Non-Ferrous Metals and Gold

LLC “Engineering-Technological Center “RUSAL”, Saint Petersburg, Russia:

A. G. Suss, Director of Technological Department of Engineering-Technological Direction of Alumina Industry

This paper shows the results of scandium separation from an extremely low concentrated solution generated in carbonate-bicarbonate leaching of red muds from Ural Aluminum Plant. Calcium hydroxide was found as an effective precipitation agent. The study covers the influence of calcium hydroxide in form of lime milk on the pH level of scandium-containing solution with chemical composition, g/dm³: 51.88 total Na₂O (where 37.33 is bicarbonate of Na₂O, 14.55 is carbonate of Na₂O), 0.0077 Sc₂O₃, 0.29 ZrO₂, 0.31 TiO₂. Even a small exceed of CaO allows separating of 90% scandium in solid phase while keeping 95% of zirconium in solution. We investigated the effect of temperature and duration of precipitation process on behavior of scandium and co-following zirconium and titanium (as well as chemical and physical compositions of precipitations). Tiff is a basic phase that contains Sc₂O₃ up to 0.3% (wt.). The work demonstrates that limewater effectively precipitates scandium oxide, and separates the high concentrated bicarbonate bypass solutions. This allows keeping down the costs on pulp aeration of carbonate-bicarbonate leaching. Based on the larger-scale testing data, technological parameters for scandium separation using limewater are recommended. Scandium can be extracted from Ca – Sc residues by sulfuric acid. Dynamics of behavior of pulp pH level and temperature influence on separation rate of scandium, titanium, and zirconium into solution is studied. Acidic liquors after sulfuric treatment have the following chemical composition, g/dm³: 0.878 CaO, 0.055 TiO₂, 0.033 Sc₂O₃, 0.004 Al₂O, 0.002 ZrO₂. Reagents consumption factors are derived for lime and concentrated sulfuric acid. The study shows that proposed method enables higher throughout recovery of Sc₂O₃ from carbonate-bicarbonate solutions up to 82%.

This article was written within the fulfillment of the subsidiary agreement No. 14.578.21.0014 (5 June 2014) (unique identifier: RFMEFI57814X0014) between the National University of Science and Technology “MISiS” and the Ministry of Education and Science of Russian Federation, within the realization of the Federal Target Program “Investigations and Developments on the priority ways of development of scientific-technological complex of Russia for 2014–2020 years”, approved by the decision of the Government of the Russian Federation (28 November 2013) No. 1096.

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