Institute of Solid State Chemistry of Ural Branch of Russian Academy of Sciences, Ekaterinburg, Russia:
L. A. Pasechnik, Senior Researcher, e-mail: pasechnik@ihim.uran.ru
A. S. Yatsenko, Senior Researcher
S. P. Yatsenko, Head of Laboratory
L. M. Skryabneva, Engineer

This article shows the study of partial dissolution of alumina industry red mud by hydrochloric and sulfuric acids. Extraction of the basic components (Fe, Al, Ca, Ti), scandium, and yttrium was determined, depending on the depth of treatment by acid solutions with different initial concentrations at the temperature of 90 ^oС, during 1 hour. There were found the optimal conditions of partial mud dissolution, which provide more than 80% extraction of yttrium and only several percent extraction of iron, aluminum, titanium, and scandium in diluted sulfuric acid. Calcium, readily extracted by hydrochloric acid, can be later removed by sulfates extraction with following transformation into anhydride. The content of yttrium in solution can be increased to 0.18 g/dm³ by recycling of acid solutions during the red mud treatment. Yttrium was sorbed at the value of рН = 2–5 on H-shaped KU-28 (КУ-28) cation exchanger. Desorption was carried out by a mixture of sodium sulfate and sulfuric acid or by 1M solution of sulfuric acid. For the purpose of obtaining of yttrium-rich concentrate, it is reasonable to remove some aluminum, iron and titanium hydroxides before sorption, using the neutralization by ammonia solution. In that case, the crude concentrate contained 3–7% of yttrium oxide. Further selective extraction of yttrium includes hydrolysis, extraction by phosphorus-containing organic compounds (tributylphosphate (TBP), di-(2-ethylhexyl)phosphoric acid (DEHPA)), reextraction, and deposition and calcination of oxalates. As a result, there was obtained the 99.0% yttrium oxide. The scale of yttrium production was calculated on the basis of demand for coagulant, required for waste water treatment, when sulfuric acid is replaced by liquid coagulant, produced simultaneously with yttrium extraction. This amount of coagulant provides the production of 3000 kg of yttrium oxide. At the same time, 6800 t of anhydrite will be produced. Consumption of basic chemical reactants for processing of 30,000 t of red mud is estimated. The payback period of the project is 3.5 years.

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