Selective Leaching of Scandium and Yttrium from Bayer Red Mud by Citric Acid
Citric acid was used as leaching agent,the effects of different citric acid concentrations,leaching times,liquid to solid ratios and leaching temperatures on the leaching rates of scandium,yttrium and iron from red mud were investigated,and the process parameters were optimised by orthogonal tests.The results show that the selective leaching effect of scandium and yttrium is the best under the conditions of citric acid concentration of 0.8 mol·L-1,leaching time of 45 min,liquid-solid ratio of 12∶1 mUg,and temperature of 80 ℃.The temperature has a significant impact on the leaching effect,and the leaching rates of scandium,yttrium,and iron are 88.79％,91.93％,and 5.42％,respectively.The XRD and SEM-EDS analysis results indicate that citric acid has different decomposition abilities for different minerals in the red mud and poor solubility for hematite,which makes it have good selectivity for leaching scandium and yttrium with iron.The process of scandium leaching conforms to the multiphase liquid-solid reaction model,and yttrium leaching conforms to the shrinking-core reaction model.The apparent activation energies of scandium leaching are 43.68 and 52.51 kJ·mol-1,respectively,and the reaction processes of both are controlled by chemical reactions.
red mudcitric acidrare earth elementsacid leachingselectivity
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