Recovery of Rare-Earth Elements from Neodymium Magnet Waste Using Glycolic, Maleic, and Ascorbic Acids Followed by Solvent Extraction
Tóm tắt
Rare-earth elements (REEs) play a key role in modern societies as their usage keeps increasing in new technologies and green energy sources. However, they are also considered the most critical raw materials in the EU and the USA in terms of supply. There is an increased global interest in the recycling of REEs from end-of-life products and industrial waste. Some REEs, such as Nd, Pr, and Dy, can be recovered from neodymium magnets. These magnets are of special interest since they are present in various technological wastes, such as hard disk drives, electric generators for wind turbines, electric motors, etc. Separation of REEs from other magnet components, such as Fe, which is the main part of the alloy, and further reprocessing of REEs, is the main goal of this work. In this work, neodymium magnet powder was successfully leached using the fully combustible organic lixiviants maleic, glycolic, and ascorbic acids, in order to potentially decrease the usage of strong mineral acids in the hydrometallurgical recovery of REEs. Subsequently, the REEs were selectively extracted from these leachates. For this separation step, several phosphate extractants (TBP, D2EHPA, Cyanex 272, and 923) were investigated, alongside TODGA, which follows the CHON principle and is fully combustible, with no ash or acidic gases being produced. The influences of various diluents (1-octanol, cyclohexanone, hexane, pentane, and dodecane) on the extraction were also studied since the diluents can play an important role in the extraction process and increase selectivity between the extraction of REEs and other impurities. Leaching was shown to be more efficient with maleic and glycolic acids than with ascorbic acid, even at room temperature. Values above 95% were reached for REEs with 1 M concentration and 1/80 solid/liquid ratio. For ascorbic acid, heating the leaching system to 70 °C allowed similar values to be reached. D2EHPA has shown good extraction properties for the recovery of REEs from both glycolic and maleic leachate, mostly with nonpolar diluents such as pentane and hexane, without extracting transition metals (distribution ratios under 0.1). TODGA also showed good extraction of REEs and selectivity between elements, but only in the maleic leachate. As expected, the increasing concentration of the D2EHPA led to the increased distribution ratios. Thus, glycolic, maleic, and ascorbic organic acids, which have not been used before for leaching of neodymium magnet waste, showed good potential for the recovery of REEs from neodymium magnets and for the further development of large-scale recovery processes for REEs.
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