(2,3-Dimethylbutyl)(2,4,4′-trimethylpentyl)phosphinic acid (INET-3) was impregnated onto dry macroporous resins XAD-16 and pretreated XAD-16 with ethyl alcohol and HCl (Pre-XAD-16) to prepare the solvent impregnated resins SIRs-INET-3/XAD-16 and SIRs-INET-3/Pre-XAD-16. The molecular weight distribution of the low molecular weight (LMW) polymers washed off by ethyl alcohol during XAD-16 pretreatment was determined by gel permeation chromatography (GPC). The macroporous resins (XAD-16 & Pre-XAD-16), the corresponding solvent impregnated resins (SIRs-INET-3/XAD-16 & SIRs-INET-3/Pre-XAD-16) and the PVA coated SIRs-INET-3/Pre-XAD-16 with boric acid as cross-linking agent were characterized by FT-IR, SEM-EDS and TGA . The effects of XAD-16 pretreatment and PVA coating technology on RE(III) adsorption equilibrium time, INET-3 losses during extraction and adsorption capacity were investigated. The adsorption kinetics , selectivity and stripping behaviors of SIRs-INET-3/XAD-16 were further studied. The washed off LMW polymers had the Mn of 36,656, Mw of 40,310 and polydispersity coefficient of 1.10. The SIRs-INET-3/XAD-16 had shorter equilibrium time, less INET-3 loss and more Tm(III) adsorption capacity than the SIRs-INET-3/Pre-XAD-16. The PVA coated SIRs-INET-3/Pre-XAD-16 had less INET-3 loss and more Tm(III) adsorption capacity but longer equilibrium time than the uncoated SIRs-INET-3/Pre-XAD-16. The adsorption of RE(III) on the SIRs-INET-3/XAD-16 followed the pseudo-second-order kinetic model . The Tm(III) accumulative adsorption amounts onto SIRs-INET-3/XAD-16 after eight extraction stages was 23.6 mg/g. The separation factors of adjacent heavy RE(III) β Er/Ho , β Tm/Er , β Yb/Tm and β Lu/Yb values were 1.76, 2.59, 2.56 and 1.19, respectively. The adsorbed Lu(III) onto the SIRs-INET-3/XAD-16 can be stripped completely by 1.0 mol/L H 2 SO 4 .
Nonsymmetric (2,3-dimethylbutyl)(2,4,4′-trimethylpentyl)phosphinic acid (INET-3) may be a superior extractant for extraction and separation of heavy rare earths (REs), as its extraction ability falls between that of P507 and Cyanex 272. Its purity and pK a were determined using potentiometric titration methods. The extraction mechanism and extraction equilibrium constants of INET-3 for heavy REs from chloride media were studied. The effects of the anion types (Cl − , NO 3 − and SO 4 2 − ) and concentrations (0.1, 0.5 and 1.0 mol/L) on RE(III) extraction were investigated. The extraction capacity and separation factors of INET-3 for heavy REs were determined. The stripping behaviours of heavy RE complexes with INET-3 by HCl , HNO 3 and H 2 SO 4 were examined. The results showed that the pK a of INET-3 was 5.45. The extraction capacity of INET-3 was approximately twice that of Cyanex 272 and only one-third that of P507. Loaded heavy RE(III) extracted by INET-3 was completely stripped out by HCl, HNO 3 and H 2 SO 4 solutions when the pH was at or below 1.2. Among the three inorganic acids , H 2 SO 4 was the most effective stripping agent. INET-3 can separate heavy RE(III) efficiently, and the separation factors of adjacent heavy RE(III) β Er/Ho , β Tm/Er , β Yb/Tm and β Lu/Yb were 3.25, 2.73, 2.96 and 1.53, respectively, when extracted from a Ho/Er/Tm/Yb/Lu quinary system.
Zhengyu Liu,Jiaming Wu,Xinyu Liu,Wen Wang,Ziwei Li,Ruijing Xu,Yue Ding,Junlian Wang
Rare earths (REs) and Co are critical strategic resources. Their recovery is crucial for ensuring that their supplies are adequate and for reducing environmental pollution. End-of-life NdFeB magnets are important secondary RE sources. The separation of Dy, Nd, and Co from NdFeB leachate using a relatively new extractant (2,3-dimethylbutyl) (2,4,4′-trimethylpentyl)phosphinic acid (INET-3), was investigated in this study. The separation parameters, such as equilibrium pH, phase ratio, INET-3 concentration, and number of counter-current extraction stages, were optimised. The results show that INET-3 can separate Dy, Nd, and Co efficiently. For the preferential extraction of Dy from synthetic iron-free NdFeB leachate, the optimum equilibrium pH is 2.60. Under this condition, separation of Dy from the leachate requires four counter-current extraction stages at A/O (volume ratio of aqueous to organic) = 1:2. This is demonstrated by a simulated four-stage counter-current extraction process. At equilibrium pH = 2.52 and A/O = 1:2, 98% of Dy is recovered with 95% purity. As to the subsequent separation of Nd from the leachate, nearly 100% is recovered with 99% purity through a simulated three-stage counter-current extraction process at equilibrium pH = 5.33 and A/O = 1:1. Approximately 95% of Co remains in the raffinate with 99.98% purity.
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