Recovery of Rare Earth Elements from the Leaching Solutions of Spent NdFeB Permanent Magnets by Selective Precipitation of Rare Earth Oxalates

Abstract

After mechanical pre-treatment, the typical hydrometallurgical route of NdFeB magnet recycling starts with leaching in acidic solutions. However, due to the high concentration of iron ions in the leaching solution, the selective recovery of rare earths from the solution is challenging. In our work, the selective precipitation of rare earth oxalates as a potential separation method was proposed. The precipitation of neodymium oxalate was first tested on model solutions, which was then followed by experimental tests carried out on real solutions after the leaching of NdFeB magnets. The recovery of rare earths in the form of oxalates was investigated with the use of different amounts of oxalic acid in relation to its stoichiometric amount. The most efficient separation of rare earths was observed in the case where sulfuric acid was used for leaching. The use of oxalic acid in stoichiometric amounts resulted in the precipitation of about 93% of all rare earths present in the solution, whereas the concentration of Fe and other elements (Ni, Co, and B) practically did not change. An increase in oxalic acid of 20% and 40% more than the stoichiometric amount (100%) led to the increase in the precipitation efficiency of rare earths to 96.7% and 98.1%, respectively. However, the use of oxalic acid in a 1.4 ratio caused a 7% decrease in Fe concentration, which suggests Fe co-precipitation. In order to investigate a possibility of further increasing the separation of rare earths from iron, an additional method was tested, in which iron was first oxidized from Fe2+ to Fe3+ before the precipitation of rare earth oxalates.

High-Performance Solid-Phase Extraction Chromatography for Recycling of NdFeB Magnet Waste

“…The REE fractions can be recovered using oxalic acid precipitation, which is highly selective for REEs and enables near-complete recovery as rare earth oxalates [27]. Oxalic acid precipitation does not offer separation of the different REEs, and therefore, the desired metal composition should be achieved before recovery by oxalate precipitation.…”

Semicontinuous Process of Rare Earths Recovery from End-of-Life NdFeB Magnets on a Large Laboratory Scale

“…In our previously published studies [19,20], the NdFeB magnet recycling process based on leaching in hydrochloric and sulfuric acids followed by the selective precipitation of rare earth oxalates was investigated. The leaching process with the use of hydrochloric and sulfuric acids allowed for the dissolution of REEs and Fe whereas the metallic nickel layer, which covers the magnets, was left in the solid state.…”

“…In the precipitation process, oxalic acid was used as a precipitant. The use of oxalic acid in a 20% excess compared to its stoichiometric amount allowed the achievement of a higher precipitation efficiency of rare earths [20]. An even higher rare earths precipitation efficiency, about 99%, was also possible but required the use of a bigger excess of oxalic acid and involved the co-precipitation of iron oxalate.…”

“…After the leaching, a separation method of rare earths from the solution was investigated. Based on the conducted experiments, it was indicated that it is possible to selectively precipitate rare earth oxalates from leaching solutions without the co-precipitation of iron or other elements present in the solution [20]. The aim of the current study is to investigate the possibility of regenerating the leaching agents as well as water recovery in the proposed process.…”