Separation of Heavy Rare-Earth Elements from Light Rare-Earth Elements Via Solvent Extraction from a Neodymium Magnet Leachate and the Effects of Diluents

Abstract

In recent decades, rare-earth elements (REEs) have seen a considerable increase in usage in modern technologies and the so-called green energy sources. The REEs are currently regarded to be among the most critical elements by the European Union (EU) and the United States (USA). Large investments are made in the research of recycling of the REEs from end-of-life products and E-scrap. One potential source for recycling of larger amounts of neodymium and dysprosium are end-of-life neodymium magnets. In this work, the selective extraction of REEs from a sulfuric media leachate (containing Nd, Dy, Pr, Gd, Co, and B) obtained by selective roasting of NdFeB waste and leaching was investigated. The extracting agent D2EHPA (di-(2-ethylhexyl) phosphoric acid) diluted in Solvent 70, hexane, octane, cyclohexanone, chloroform, 1-octanol, and toluene was used for the investigation of the effects of using different diluents on the extraction of REEs and the separation between the light and the heavy REEs. The concentrations of D2EHPA in the used diluents were 0.3, 0.6, 0.9, and 1.2 M. The highest separation factors between the heavy and the light REEs were achieved using 0.3 M D2EHPA in hexane, while no B or Co extraction was measurable. The REEs were completely extracted as a group using 0.9 M or 1.2 M D2EHPA in either octane or hexane, also with no B or Co extraction. The aliphatic nonpolar diluents showed better properties than the aromatic and polar ones. The complete stripping of REEs from the loaded organic phases was proven to be efficient using hydrochloric acid at concentrations of 2 M or higher.

Leaching and Recovery of Rare-Earth Elements from Neodymium Magnet Waste Using Organic Acids

“…This can be attributed to the equilibrium pH values, which were around 3.5 after the extraction from 1 mol/L acetic acid leachate and slowly increased with the decreasing D2EHPA concentration but stayed around 1.5 after the extraction from 1 mol/L citric acid leachate. As shown in a previous study [36], higher equilibrium pH values gave higher distribution ratios for REEs due to REE-D2EHPA complex formation, which is favored in higher equilibrium pH media as D2EHPA is an acidic extractant that exhibits the ion-exchange mechanism, with release of H + ions after the complex has been formed (Equation (3)). The behavior of B and Co was also monitored in the extraction process.…”

Solvent extraction modeling of Ce/Eu/Y from chloride media using D2EHPA

“…The ionic radii of HREEs are smaller than that of LREEs because of the lanthanide contraction. Hence, the Y(III) charge density is higher than that of Eu(III) and Ce(III) . In Figure c, the effect of chloride concentration on the REE extraction is shown.…”

Recent advances on hydrometallurgical recovery of critical and precious elements from end of life electronic wastes - a review

“…It is known that the extraction efficiency of aliphatic diluents (such as hexane, octane, and Solvent 70), is higher than the polar diluents (such as cyclohexanone, 1-octanol, and chloroform) (Mohammadi, Forsberg, Kloo, De La Cruz, & Rasmuson, 2015). In recent times, solvent extraction is applied to many electronic waste materials like spent LCDs (Yang, Kubota, Baba, Kamiya, & Goto, 2013) and spent NdFeB magnets (Gergoric, Ekberg, Steenari, & Retegan, 2017). Bis(2-ethylhexyl) phosphoric acid D2EHPA (or DEHPA), tributyl phosphate TBP, bis(2,4,4-trimethylpentyl) phosphinic acid Cyanex 272, or a mixture of different phosphine oxides known as Cyanex 923 are some of the common extractants used to recover critical metals (Kri stofov a, Rudnik, & Mi skufov a, 2017).…”

“…Riaño and Binnemans (2015) demonstrated the separation of Nd and Dy by using ionic liquids in the solvent extraction process. Gergoric, Ekberg, Steenari, and Retegan (2017) studied the recovery of REE by solvent extraction from the waste NdFeB magnets leachate by using D2EHPA. The NdFeB magnets were first sulfated, roasted and leached with water to solubilize the REEs.…”