Recovery of Rare-Earth Elements from Molten Salt Electrolytic Slag by Fluorine Fixation Roasting and Leaching
Tóm tắt
Recycling waste containing rare earth has always been a research hotspot. The molten salt electrolysis process of rare-earth metals and alloys generates a large amount of waste slag, which contains high rare-earth content and, thus, has very considerable recovery value. However, the high content of fluorine in rare-earth molten salt slag brings challenges to the separation of rare-earth elements (REEs) and fluorine. So far, there are few literatures on the recovery of REEs from this slag. Although the reported alkali roasting-leaching process can recover REEs from the slag, it has serious environmental drawbacks, such as the emission of the fluorine-containing wastewater. Herein, this study presents a clean process for recycling REEs molten salt electrolytic slag. The REEs were recovered via fluorine fixation roasting using calcium oxide and calcium chloride and hydrometallurgical leaching in hydrochloric acid solution. The leaching efficiencies of REEs were > 97% under optimum conditions: roasting temperature of 973 K, calcium oxide dosage of 30%, calcium chloride dosage of 10%, HCl concentration of 3 mol/L, and leaching temperature of 363 K. In the roasting process, rare-earth fluorides were converted into oxides by calcium oxide. The addition of calcium chloride with low melting point was conducive to the reaction. The leaching residue was a calcium fluoride-rich concentrate.
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