Yoshiyuki Hirashima

Rare earth separation using a chemical vapour transport process mediated by vapour complexes of the LnCl3AlCl3 system

Abstract Mutual separations of rare earth chlorides in the PrEr, PrSm and PrNd binary systems and the PrGdEr ternary system were performed using chemical vapour transportation of vapour complexes LnAlnCl3+3n, (Ln, rare earths). Heavier rare earth chlorides were more readily transported and concentrated in the deposits in lower temperature zones while lighter ones were selectively deposited in higher temperature zones. Good separation characteristics (efficiency and purity) were observed for the resulting LnCl3 deposits by optimization of temperature gradients for the selective deposition of LnCl3 and by repeating the transport reaction. The separation factors, expressed as atomic ratios for the resulting chlorides, Pr:Er and Pr:Sm, were equal to 10.8 and 2.3 respectively.

Synergistic extraction of lanthanoids with di(2-ethylhexyl)phosphoric acid and some reagents

Abstract The effect of the addition of some reagents on the extraction of lanthanoids with di(2-ethylhexyl)phosphoric acid (D2EHPA) was studied. The reagents investigated in this study were TBP, AA, TOA and HTTA. TBP, AA or TOA gives an antagonistic effect and HTTA gives a synergistic effect. In the system of D2EHPA and HTTA the magnitude of the synergistic enhancement is relatively small, and the contribution of the synergistic extraction to the overall extraction is comparable to that of the extraction with D2EHPA alone. The synergistic enhancement decreases with increasing atomic number of the lanthanoid. From the dependence of the distribution ratio on the concentration of each extractant the following reaction is proposed for the synergistic extraction. LnX 3 ·3HX + HTTA ⇌ LnX 2 ·TTA·2HX + 2HX (HX : D2EHPA).

Distribution equilibria of SmCl3EuCl3HCl and EuCl3GdCl3HCl systems with 1M di(2-ethylhexyl) phosphoric acid in n-heptane

Abstract Distribution equilibrium data have been obtained for the systems LnCl3HClH2O1M D2EHPA in n-heptane (Ln: Sm, Eu and Gd). The equilibrium curves were described using equilibrium acid concentration as a parameter. It was shown that the distribution ratios of the lanthanides were proportional to CHX2.2 or CHX2.5 (CHX represents the concentration of the extractant) according to the estimated value for the ratio of the extractant to the metal in the extracted species. Equilibrium data for the systems involving SmCl3EuCl3 and EuCl3GdCl3 have been obtained. In these systems the concentrations of individual lanthanides in the organic phase deviated from the expected values based on the assumption that the distribution ratio of each lanthanide was not varied by adding the other lanthanides. The concentrations of the heavier lanthanides, Eu in SmEu system and Gd in EuGd system, in the organic phase were higher than the expected values, and those of the lighter lanthanides were lower than the expected values. These behaviors of the lanthanides were explained in terms of the change of the concentrations of the hydrogen ion and the extractant.

The distribution equilibria of two- and three- lanthanide systems with di(2-ethylhexyl)phosphoric acid

Abstract It was found in several two-lanthanide systems (PrNd, NdSm, SmEu, SmGd and EuGd) that the total lanthanide concentration in the organic phase changes quasi-linearly with the initial mole fractions of the individual lanthanides, and that the approximation, CLn,m(org) = ΣXiCLn,s(org), is valid, where CLn,m(org) represents the total lanthanide concentration in the organic phase, fCLn,s(org) represents the lanthanide concentration in the organic phase in the single-lanthanide system and Xi represents the initial mole fraction of the individual lanthanide. The extraction of a tervalent lanthanide with di(2-ethylhexyl) phosphoric acid (D2EHPA) can be expressed as Ln3+ + m(HX)n ⇌ LnX3 · 3HX + 3H+. From this equation the relations, D = K × CHXm × CHXm × CH+−3, CHX = CHX,i − 6CLn(org) and CH+ = CH,i + 3CLn(org), were derived when the volume ratio of the organic phase to the aqueous phase was 1:1. The distribution ratios of the individual lanthanides were estimated by using the above relations, and then the concentrations in the organic phase were calculated. The calculated values are in good agreement with the observed values. The application of the calculation procedure to the three-lanthanide systems was tried. It was confirmed that the approximation, CLn,m(org) = ΣXiCLn,s(org, is valide also in the three-lanthanide system (SmEuGd). The calculated values are in good agreement with the observed values again in the three-lanthanide system.