Satbayev University, «Institute of Metallurgy and Ore Beneficiation» JSC (Almaty, Republic of Kazakhstan):

Abdulvaliev R. A., Head of Laboratory, Candidate of Engineering Sciences, rin-abd@mail.ru
Gladyshev S. V., Leading Researcher, Candidate of Engineering Sciences, gladyshev.sergey55@mail.ru
Akhmadieva N. K., PhD, Leading Engineer
Imangalieva L. M., Leading Engineer, leila.imangalieva@mail.ru

The studies included deep processing of the hydrogranate sludge obtained by red mud leaching in a solution containing 240 g/dm³ Na₂O, in the presence of calcium oxide in the amount necessary to obtain the ratio of CaO / SiO₂ = 3, at the temperature of 240–260 ^оC. The leaching process yielded the sludge containing ferrous hydrogranate 3СаО·Fe₂O₃·2SiO₂·2H₂O as the main phase. In contrast to red mud, hydrogranate contains almost no aluminum or alkali: in the leaching process, these are transferred into the solution and returned to alumina production. The hydrogranate sludge was then subjected to reduction smelting, resulting in its good separation into cast iron and slag. The non-magnetic fraction containing REE was then extracted from the slag by magnetic separation. The iron recovery values were 88.0 % for cast iron, 11.9 % for the magnetic fraction, and 0.1 % for the non-magnetic fraction. The recovery of REE in the non-magnetic fraction amounted to 65.7 %. The magnetic fraction of the slag was used as the circulating material for the production of cast iron. The non-magnetic fraction was subjected to hydrometallurgical processing, including preliminary chemical treatment in a solution of sodium bicarbonate, nitrate leaching and extraction, yielding REE concentrates. After the preliminary chemical treatment, the content of the dicalcium silicate (larnite) phase in the slag decreased, the amounts of other phases increased, and the amorphous silica phase emerged. After the chemical treatment, the degree of REE recovery from slag to the nitric acid solution was 96 %. Tributyl phosphate was used to extract REE from this solution. Reextraction of REE from tributyl phosphate was performed using water. Oxalic acid solution was then used to precipitate REE from the reextract; concentrates with the mass fractions of ΣREE_ox equal to 17.74 and 21.58 % were obtained after washing, drying and calcination at 900 ^оC.
The work was completed with the financial support of the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan under grant No. AP05130549.

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