Destruction of mineral components of red mud during hydrothermal extraction of scandium

Abstract

The technology of scandium extraction from red mud of bauxite processing by hydrochemical method has been developed, including preliminary treatment of red mud with alkaline solution for aluminum extraction, subsequent thermochemical transformation in sodium hydrogen carbonate solution and repulping in solution containing a mixture of sodium carbonate and sodium hydrogen carbonate and sorption extraction of scandium from carbonization solution. As a result of pretreatment of red mud with alkaline solution, with the addition of CaO at the rate of obtaining the ratio of CaO:SiO₂= 1:1 in the pulp at a temperature of 240-260°C extraction of aluminum obtained in the solution more than 80%. To increase the degree of extraction of scandium, thermochemical transformation of the phase composition of red mud by treatment with sodium hydrogen carbonate solution at a temperature of 260°C, duration of 6 hours and the ratio L:S = 10. Extraction of scandium from red mud is carried out by pulp repulping method with soda-hydrocarbonate recycling solution containing Na₂O_tot = 65 g/dm³ at NaHCO₃/Na₂CO₃ ratio~ 2 with solution gassing with carbon dioxide to reach pH≤9 at temperature 80°C and duration 3 hours. According to the developed technology the degree of scandium extraction from red mud amounted to 86.5%. The efficiency of the technology is associated with the destruction of mineral components of red mud as a result of two-stage transformation of the phase composition, its recrystallization and release of the difficult-to-discover part of scandium. The analysis of existing technologies of sorption extraction of scandium from sulfuric acid leaching solutions was carried out, which showed that the best selectivity for scandium is possessed by ion-exchange resins synthesized by phosphorylation of copolymers of styrene and divinylbenzene. When using phosphorus-containing amphoteric ionite Lewatit TP 260, the degree of scandium extraction from the carbonization solution was 98%.