Leaching Behavior and Kinetics of Scandium and Yttrium from Bayer Red Mud
A two-step acid leaching process was used to leach scandium and yttrium from red mud.Phosphoric acid was used in the first stage of leaching to achieve dealkalization,desilication and enrichment of rare earth elements(scandium and yttrium).Then,the leaching residue was leached with sulfuric acid in the second stage.The effects of sulfuric acid concentration,liquid-solid ratio,reaction temperature and reaction time on the leaching process of scandium and yttrium were investigated,and the leaching kinetics was also analyzed.It is found that leaching of red mud with phosphoric acid can bring better dealkalization and desilication effect,showing the leaching rates of K,Na and Si at 75.62%,87.82%and 80.25%,respectively.Then,in the second stage of leaching process with sulfuric acid concentration of 2.5 mol/L and liquid-solid ratio of 7∶1,reaction runs at 70 ℃ for 45 min,leading to the average leaching rates of Sc and Y up to 74.49%and 80.02%,respectively.It is shown that the leaching processes of Sc and Y with sulfuric acid follow the liquid-solid reaction model,which is controlled by diffusion,and the apparent reaction activation energies are calculated to be 18.50 kJ/mol and 16.74 kJ/mol,respectively.
Bayer red mudacid leachingscandiumyttriumkineticsphosphoric acid leachingsulfuric acid leaching
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