The recycling of the rare earth neodymium (Nd) is vital to providing greener technology for many industries. In this paper its recovery from waste permanent magnets (WPMs) is explored using a hydrometallurgical process involving separation using hollow fiber supported liquid membranes (HFSLMs). After demagnetization, the options for WPMs leaching were investigated by varying mineral acids, acid concentrations and solid/liquid (S/L) ratios. The separation Nd from iron (Fe) was carried out by precipitation using oxalic acid. Nd in WPMs was recovered by solvent extraction using D2EHPA in Isopar-L. The influence of various parameters such as pH and organic/aqueous (O/A) phase ratio were investigated. Optimum leaching was achieved using 3 M H₂SO₄ with an S/L ratio of 1 g/50 mL to obtain 485 g/kg of Nd. Nd-separation from Fe was successfully performed using 0.6 M D2EHPA with an O/A phase ratio of 3 at a pH of 1.26 – 2.0 resulting in Nd-recovery of 97.48%. The optimum stripping was achieved using 6 M HNO₃. In the HFSLM experiments, the concentration of Nd in the aqueous strip solution was 4120 mg/L whilst that in the aqueous feed solutions was 658 mg/L. The HFSLM module used recovered 90.82% of the Nd within 35 min.

The properties of four different extractants, TODGA (N,N,N',N'-tetraoctyl-diglycolamide), T2EHDGA (N,N,N',N'-tetraisooctyl-diglycolamide), DPDODGA (N,N'-dipropyl-N,N'-dioctyl-diglycolamide) and DIPDODGA (N,N'-diisopropyl-N,N'-dioctyl-diglycolamide), to extract heavy rare earth metal ions in hydrochloric acid were studied to understand the relationship between the chemical structure of the extractant and the extraction properties of rare earth metal ions. The extraction order of heavy rare earths in n-octane: n-octanol = 9:1 diluent was as follows: DIPDODGA > DPDODGA > TODGA > T2EHDGA. Alkyl chain shows great influence on extraction ability and the extractants with short chain can effectively extract heavy rare earth ions even at a concentration of less than 1.0 mol/L. The extraction mechanism was proposed with the results of slope methods, IR (Infrared) spectrometer and DFT (Density Functional Theory) theoretical study. T2EHDGA forms binuclear and the other three extractants form mononuclear extracted species with heavy rare earth ions.

Separation of scandium (Sc) and yttrium (Y) using solvent-impregnated resin (SIR) containing bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) along with 1-octanol as a modifier was investigated. 1-Octanol was added to enhance stripping efficiency, since stripping of heavy rare earths from the organic solution containing organophosphorus extractants is difficult. The coated SIR was applied to both batch and chromatographic recovery of Sc and Y. The adsorption of Sc followed the Langmuir isotherm model. Separation of Sc from Y was achieved by employing chromatographic adsorption system together with quantitative elution from SIR by 5 mol/L HCl.

In(III) and Ga(III) are included in zinc refining, the wastes of solar panel and electronics and so on. In solvent extraction which is a useful method of separation of metals, we used N-lauroylsarcosine (NLS), containing tertiary amine which is alkyl amide derivative with the sarcosine moiety in the molecule structure in order to separate and recover these metal ions. We studied about the extraction equilibria of these metals using NLS. The selective extraction order of NLS is Ga(III) > In(III) >> Zn(II). It was found that NLS was able to separate these metals by pH difference. Versatic acid 10 (VA10) with only carboxylic acid group in the molecule structure extracted In(III) and Ga(III) simultaneously in the same pH region. Therefore, we found that the amide group included in the molecule structure of NLS has an important role to extract these metals. Mutual separation of In(III), Ga(III) and Zn(II) was carried out by a one-step experiment using NLS. Slope analysis was used to investigate the extraction equilibria of In(III) and Ga(III) with NLS. Suitable concentrations of acids were able to strip these metals from the loaded organic phase.

The extraction of the Eu(III) thenoyltrifluoroacetone (TTA) chelate was investigated by using the nonionic surfactant octylphenoxypolyethoxyethanol (Triton X-114, n = 8). A cloud point extraction (CPE) method is proposed for the preconcentration of Eu(III) and subsequent determination was carried out by a fluorometric method using a microwell plate reader. Optimal experimental conditions were examined for fluorescence of the TTA chelate in the surfactant phase. Fluorescence was measured at λ_em = 616 nm after excitation at λ_ex = 355 nm. The extracted species is estimated to be Eu(TTA)₃(Triton X-114)_1~2 and coordination is competitive between TTA and the oxygen atoms of Triton X-114 depending on each concentration. A content of Eu(III) was directly determined by a plate reader using 100 mm³ of surfactant phase without dilution. The fluorescence intensity, which was measured in a microwell, was a linear function of initial concentration from 1.0 × 10^-8 to 8.0 × 10^-6 mol dm^-3 of Eu(III). The use of microwell plate system is convenient for handling small-volume samples.

The partitioning behavior of horseradish peroxidase (HRP) to phospholipid- and surfactant vesicles has been analyzed. Peripheral binding of the zwitterionic phospholipid vesicle membranes is proposed with insertion into the membrane interior of negatively charged surfactant vesicles, resulting from non-electrostatic interaction. The insertion of HRP is interpreted by considering the interaction between headgroups of phospholipid and between headgroups of surfactant.

“Emulsion-flow” is a unique regime of counter-current contact between aqueous and organic phases in a column extractor. The operation enables fast mass transfer as well as stable dropwise counter-current of both phases in a simple column-type apparatus. While those advantages have been reported, prediction of the column performance has been difficult because of the lack of correlation with mass transfer coefficient and interfacial area. This study suggests correlation with overall aqueous phase mass transfer capacity coefficient, K_wa and the height of emulsion phase, H for various operating conditions. In iodine extraction, velocity of organic phase had a stronger effect on H. Furthermore K_wa was correlated with a root of H. This fact suggests that the velocity of the organic phase plays a major role in mass transfer for the case of emulsion-flow. Correlations suggested in the present study are important for rational design and scaling up of emulsion-flow columns.

Extraction of ruthenium(III) from hydrochloric acid solutions was investigated at 25°C by using a protic ionic liquid, trioctylammonium chloride ([HTOA]Cl), as an extraction solvent. Extraction percentages of more than 99% were obtained under the following conditions: volume ratio of aqueous to ionic liquid phase = 1; shaking time ≥ 12 h; aqueous HCl concentration (C_HCl) = 4.0 mol/L. The D vs. C_HCl plot shows a bell-shaped curve with the maximum D = 106 at C_HCl = 4.0 mol/L. Several other ionic liquids were also examined as extraction solvents, and trihexyltetradecylphosphonium chloride ([THTDP]Cl) was found to have a higher extraction efficiency (D = 8 × 10² at C_HCl = 4.0 mol/L) than [HTOA]Cl. By using 1.0 mol/L aqueous thiourea as a stripping solution, 100% of the metal was back-extracted from [HTOA]Cl, whereas only 21.4% was back extracted from [THTDP]Cl. The possibility of extraction separation of ruthenium(III) from other metals was also investigated.

Phenylalanine, which is an essential amino acid, is used as a nutritional supplement. Development of a more effective separation technique from the broth is desired. We conducted permeation of phenylalanine through PVC-based membrane containing bi-functional ionic liquid consisting of Aliquat 336 and bis(2- ethylhexyl)phosphoric acid (D2EHPA), [A336][D2EHPA], as a carrier. Phenylalanine successfully permeated through PIMs containing [A336][D2EHPA]. The permeation rates through PIM containing [A336][D2EHPA] were higher than those using a conventional ionic liquid, Aliquat 336. From the experimental data, the overall mass transfer coefficients were calculated and the feed film resistance was found to control the permeation process in a flat-sheet permeation apparatus.