Hirokazu Narita

Chapter 255 - Recycling of Rare Earths from Scrap

Abstract With the increased concern about the rare-earth supply chain risk, recycling rare-earths from scrap is receiving significant attention. In this monograph, the studies of the rare-earth recycling technologies have been reviewed with respect to magnets, phosphors, batteries, polishing powders and others from the viewpoints of physical separation, hydrometallurgy, and pyrometallurgy. The important issues inherent in each scrap were pointed out. Particularly-important issues are dismantling, demagnetization, the separation from iron for the magnets, and the fine particle separation and the terbium dissolution for the phosphors. Emerging technologies, such as the automated dismantling methods for the magneta and the application of high gradient magnetic separation for the phosphors, together with a new extractant have been noted. A cost barrier before the actual implementation of the developed process should be overcome not only by the technologies, but also by the integration with a social system establishment.

Extraction of Lanthanides with N,N′‐Dimethyl‐N,N′‐diphenyl‐malonamide and ‐3,6‐dioxaoctanediamide

Abstract The extraction properties of the trivalent lanthanides (Ln(III)) with the bidentate N,N′‐dimethyl‐N,N′‐diphenyl‐malonamide (MA) and the tetradentate N,N′‐dimethyl‐N,N′‐diphenyl‐3,6‐dioxaoctanediamide (DOODA) were investigated. These diamides formed by coupling two amide groups with methylene and/or ether groups are bidentate for the MA and tetradentate for the DOODA. By adding a previous data regarding the tridentate N,N′‐dimethyl‐N,N′‐diphenyl‐diglycolamide (DGA), these extraction results enabled us systematically study an effect of number of oxygen donor on its extraction behavior of Ln(III). The change in the distribution ratios (Ds) of Lu(III) with an increase in the HNO3 concentration is greater than that of La(III) in both the MA and DOODA systems. Therefore, the relationship between the D and atomic number, i.e., the lanthanide pattern, changes with the HNO3 concentration: the Ds decrease with an increasing atomic number at lower HNO3 concentrations. The Ds of the lighter Ln(III) are similar to the Ds of the heavier Ln(III) at higher HNO3 concentrations. The number of the extractant in the extracted species for La(III) and Lu(III) obtained from slope analysis at 4 M HNO3 in the MA system are about 3, while those in the DOODA system are quite different, i.e., 2 for La(III) and 1.5–3 for Lu(III). The comparison of the extractability of Ln(III) by MA, DOODA, and DGA shows that the magnitude of the Ds is in the sequence of MA < DOODA ≪ DGA. This suggests the introduction of one ether oxygen atom to the principal chain in the diamides leads to a good extractability for the Ln(III) from HNO3 solution.

The first effective extractant for trivalent rhodium in hydrochloric acid solution

The first effective extractant capable of the selective recovery of rhodium3+ from hydrochloric acid solution, N-n-hexyl-bis(N-methyl-N-n-octylethylamide)amine (HBMOEAA), has been developed.

Highly Efficient Extraction of Rhodium(III) from Hydrochloric Acid Solution with Amide-Containing Tertiary Amine Compounds

Extraction of Rh(III) from a HCl solution with N,N-disubstituted amide–containing tertiary amine (ACTA) compounds (N,N-di-n-hexyl(N-methyl-N-n-octyl-ethylamide)amine (MonoAA), N-n-hexyl-bis(N-methyl-N-n-octyl-ethylamide)amine (BisAA), and tris(N-methyl-N-n-octyl-ethylamide)amine (TrisAA)) was investigated. The ACTAs extract Rh(III) more efficiently than tri-n-octylamine (TOA), and the extraction efficiency increases with increasing number of amide groups: TrisAA > BisAA > MonoAA ≫ TOA. For all ACTAs, the predominant Rh(III) complex extracted from 2 M HCl is probably {[RhCl5(H2O)]·(ACTA·H)2}. The apparent basicity of the ACTAs and TOA varies in the opposite order from that observed for the Rh(III) extraction efficiency. Rh(III) can be readily back-extracted using 10 M HCl solution possessing a high selectivity over similarly loaded Pd(II) and Pt(IV).

Structure of the Extracted Complex in the Ni(II)‐LIX84I System and the Effect of D2EHPA Addition

Abstract The structure of the Ni(II) complex extracted with the commercial hydroxyoxime, LIX84I, and the effect of adding bis(2‐ethylhexyl) phosphoric acid (D2EHPA) to LIX84I on the extraction rate and the coordination of Ni(II) were investigated by solvent extraction and XAFS methods. The XANES spectrum and the curve fits of the EXAFS spectrum of the Ni‐LIX84I complex showed that the complex is four‐coordinate square‐planar with a 1:2 stoichiometry. In the Ni(II)–D2EHPA–LIX84I system, the coordination geometry changes from square‐planar to six‐coordinate octahedral with an increase in the D2EHPA concentration. Although the rate of Ni(II) extraction from the model spent electroless nickel plating bath with LIX84I is significantly accelerated by adding a small amount of D2EHPA ([LIX84I]: 0.5 M, [D2EHPA]: 0.05 M), most of the Ni(II) complexes extracted with this organic solution remain square‐planar. This indicates that the increase in the extraction rate does not depend on the change in the coordination structure of the extracted complex.

Synergistic Extraction of Rhodium(III) from Hydrochloric Acid Solution with Tri-n-octylamine and Sulfide-type Extractants

Synergistic extraction of Rh(III) from relatively concentrated HCl solution was studied using two mixed solvents (di-n-hexyl sulfide (DHS)–tri-n-octylamine (TOA) and N,N′-dimethyl-N,N′-di-n-octyl-thiodiglycolamide (TDGA)–TOA) in chloroform. The Rh(III) extraction efficiency is poor when 0.5 M TOA, DHS, or TDGA is used independently. In contrast, the 0.5 M TDGA–0.5 M TOA and 0.5 M DHS–0.5 M TOA mixed solvents extract ˜90% and ˜70% of Rh(III), respectively, at maximum. Slope analyses and Job’s plots for the distribution ratios of Rh(III) at 2 M HCl show that the apparent stoichiometry of Rh(III):TOA:(DHS or TDGA) in the extracted complex is 1:2:1.

Extraction and Structural Properties of Rhodium–Tin Complexes in Solution

Abstract The extraction and structural properties of rhodium complexes with stannous chloride using N,N‐dioctyl hexanamide (DOHA) were investigated by solvent extraction and Rh K‐edge X‐ray absorption fine structure (XAFS) spectroscopy. In the absence of Sn(II), Rh was hardly extracted from a 1 M HCl solution. However, the Rh extraction was enhanced with an increase in the Sn(II) concentration in the initial aqueous phase. The high extractability of Rh is achieved using the 1 M solution at [Sn(II)]/[Rh] ≥ 6 as the aqueous phase. At the [Sn(II)]/[Rh] = 12, the extraction of Rh was almost 100% over the HCl concentration range from 1 to 10.5 M. The X‐ray absorption near edge structure (XANES) spectra changed with an increase in the [Sn(II)]/[Rh] value in the 1 M HCl solution, suggesting that the Rh ion was reduced from trivalent to monovalent. In the DOHA complex prepared by solvent extraction from the [Sn(II)]/[Rh] = 12–1 M HCl solution, the XANES spectrum indicated that Rh(I) is predominant. The extended X‐ray absorption fine structure (EXAFS) spectra and the obtained structural parameters showed nearly the same result for the 1 M HCl solution at [Sn(II)]/[Rh] = 12 (Rh–Sn 5.3(6) at 2.54(1) Å) and the DOHA complex (Rh–Sn 4.7(8) at 2.56(1) Å). These results suggest that the [RhI(SnCl3)5]4− complex is the predominant species in both the organic and aqueous phases when the 1 M HCl solution at [Sn(II)]/[Rh] = 12 is used as the aqueous phase and that the [RhI(SnCl3)5]4− complex is highly extractable.

Recycling Valuable Metals via Hydrometallurgical Routes

The hydrometallurgical method is one of the key technologies in metal recycling, because it enables the fine separation between chemically-similar metals and a small-scale operation. In this paper, the recent results of our hydrometallurgical recycling studies are outlined. The topics include (i) noble extractants for precious metal separation, (ii) recovery of rare-earth elements from neodymium magnet scrap, (iii) nickel recovery from spent electroless nickel plating baths, and (iv) an energy-saving copper recycling process. In (i), new amide-type solvent extraction reagents have been developed for precious metals, one of which, thiodiglycolamide, rapidly and selectively extracts palladium from platinum and has a high durability against oxidation. In (ii), a process consisting of oxidative roasting – selective acid leaching followed by solvent extraction separation of dysprosium from neodymium has been proposed. In (iii), solvent extraction using a chelating reagent is used to extract nickel ions from spent electroless nickel plating baths, and the nickel ions are recovered as a nickel sulfate solution which can be reused in the plating process. In (iv), a copper recycling process utilizing monovalent copper in an ammoniacal alkaline solution is described, which would significantly reduce the energy requirement for copper electrowinning.

Structural studies of lanthanide(III) complexes with oxydiacetic acid and iminodiacetic acid in aqueous solution by EXAFS

The local structure of the trivalent lanthanide (Ln(III)) complexes with oxydiacetic acid (ODA) and iminodiacetic acid (IDA) in aqueous solution was investigated by EXAFS spectroscopy. The coordination number and the bond distance were obtained by the detailed EXAFS analysis. The coordination number of Ln(III) in both the Ln-ODA and -IDA systems decreases from nine for lighter Ln(III) to eight for heavier Ln(III). The bond distances of ether O atoms from Ln(III) in the Ln(ODA)(3)3- complexes are shorter than those of N atoms in the Ln(IDA)(3)3- ones.

Environmentally friendly separation of dysprosium and neodymium by fractional precipitation of coordination polymers

Against a backdrop of increasing demand, the recovery of neodymium (Nd) and especially dysprosium (Dy) from manufacturing scraps and used magnets has necessitated the development of Nd/Dy separation technologies. To this end, we suggest a simple and environmentally friendly separation method by fractional precipitation of coordination polymers (CPs)—extended complexes of metal ions and organic ligands. With the di(2-ethylhexyl) phosphoric acid ligand functioning as a precipitant, Dy was exclusively precipitated as a CP due to its precipitation equilibrium that is considerably different from that of Nd.