Aliphatic Diluents Research Articles

Lipophilic EDTA-based ligands in different diluents for the extraction of rare earths: Preliminary results with Nd(III), Dy(III) and Pr(III) in chloride and nitrate media

A separation method for the recovery of neodymium(III) from two different media, chloride and nitrate, by implementing solvent extraction technique with a novel lipophilic diamide derivative of ethylenediamine tetraacetic acid (EDTA), namely 2,2’-N,N′-didecyl-dioxo-N,N′,N″,N″’-tetraazatetratriacontane-N″,N″’-diyl diacetic acid (H2E4C10), has been investigated. Initial screening results demonstrated acceptable solubility (ca. 15 mM) of the diamide in 1,3-diisopropylbenzene (DiPB) and in a 93:7 v:v n-dodecane:n-octanol mixture (DOm) as non-polar diluents. Further investigations aiming at determining operational parameters associated with the befitted extractant systems were conducted at pH ranging from 2 to 4 in chloride and nitrate media. A pH-dependent performance of the proposed systems revealed loading capacity peaking at pH = 3 with the respective values of 1.7 and 2.0 g L−1 in nitrate and chloride media. The extraction efficiency, the distribution coefficients, and the separation factor (E%,D and SF, respectively) were determined for an equimolar mixture of neodymium and two other potential competitive lanthanides, namely dysprosium and praseodymium. The best selectivity was observed in the chloride medium at pH = 4 yielding SFNd/Pr = 1.48 and SFNd/Dy = 2.03. Neodymium-to-extractant stoichiometry was evidenced in chloroform to be 1:1 H2E:Nd at pH = 2. Thermodynamic constants related to the considered extraction equilibrium have been determined by using the Van't Hoff relation and the slope analysis method. It appeared within the selected pH-range that the mechanism of the Nd3+ transfer was strongly influenced by the nature of the diluent. This was illustrated by the enthalpy-driven transfer when Nd3+ was extracted with the H2E-4C10-Dom system (aliphatic diluent) while the transfer became entropy-driven when the extraction was performed with the H2E-4C10-DiPB system (aromatic diluent). The complexation of Nd3+ involved mainly the participation of both the amide and carboxylic functional groups. The transfer of the cation to the organic phase might occur through the formation of the Nd(HE)A2 complex (where A is either a nitrate or a chloride anion), allowing for the lowest associated standard Gibbs free energy of transfer (−28 < ΔG° < −24 kJ mol−1) regardless of the aqueous feed.

Solvent extraction of titanium(IV) from orthophosphoric acid media using Aliquat-336/kerosene and stripping with nitric acid

Titanium extraction from acidic solutions was investigated using Aliquat-336, considering factors like acid type and concentration for leaching, diluent type for solvent extraction, equilibration time, extractant concentration, phase ratio, and temperature. Kerosene exhibited superior performance as an aliphatic diluent for Aliquat-336 compared to other utilized diluents. The extraction efficiency was inversely proportional to the dielectric constant of the diluents. The quantitative Ti(IV) extraction efficiency from phosphoric acid (6 M H3PO4) leach liquor of ilmenite and rutile achived 98 % at room temperature (298 K) in 10 min after mixing with 0.1 M Aliquat-336 dissolved in kerosene at a phase volume ratio of 1:1 (Aq:Org). The exothermic extraction process occurred spontaneously. The proposed extraction mechanism using Aliquat-336/kerosene involves ion-pair association of the extractant with a Ti(IV) complex, confirmed by FTIR spectroscopy. The Ti(IV) ions were effectively stripped using HNO3 (3 M) with an aqueous:organic phase volume ratio of 1:1 at 25 °C after a contact time of 10 min in each step. The Aliquat-336/kerosene efficiently tested for Ti(IV) recovery from acidic Abu-Ghalaga ilmenite and rutile leachate. The findings indicate that, the phosphate medium is highly efficient in extracting Ti(IV), even with low concentration of Aliquat-336 in kerosene, especially in comparison to the impurities such as Fe, Cr, and Al. The EDX, XRD, and wet chemical analyses of the final product after the hydrolysis of stripped Ti(IV) from samples originating from the Abu-Ghalaga area and rutile samples, confirmed the formation of high-purity TiO2 (predominantly anatase phase). The SEM results showed particles with a regularly spherical structure and uniform size.

Predictive thermodynamic model for solvent extraction of Iron(III) by tri-n-butyl phosphate (TBP) from chloride media

Hydrometallurgical processes are crucial to reducing the environmental impact of metal recovery, yet dealing with iron impurities is a major challenge. This paper presents a semi-empirical predictive thermodynamic model for iron removal from chloride media by solvent extraction with tri-n-butyl phosphate (TBP). This model is built upon the OLI mixed-solvent electrolyte framework (OLI-MSE). It goes beyond traditional thermodynamic models by incorporating the non-ideality of both the aqueous and organic phases in a single, chemistry-based thermodynamic model. On top of the OLI-MSE framework lies the chemical model that depicts the extraction of Fe(III) by forming an ion pair between the FeCl4– anion and protonated TBP (TBPH+) in the organic phase. The iron(III)-containing ion pair in the organic phase is further stabilized by interactions with neutral TBP molecules. Developing the model required modeling the Fe(III) – chloride chemistry in the aqueous phase, optimizing the HCl extraction model, and fitting the parameters between FeCl4–, TBPH+, and TBP to experimental solvent extraction data. The resulting thermodynamic model can predict the solvent extraction of iron(III) from complex feed solutions by TBP in aliphatic diluents at all concentrations up to undiluted TBP. It can be used to calculate the equilibrium energies and composition, and the species present at equilibrium.

Conversion of Lithium Chloride into Lithium Hydroxide Using a Two-Step Solvent Extraction Process in an Agitated Kühni Column

A significant consequence of the green transition is the growing demand of lithium-ion batteries (LIBs), as they are essential for electrical vehicles. In turn, the demand for the raw materials that are needed to produce LIBs is increasing. A common LIB cathode type for electrical cars is lithium nickel manganese cobalt oxide (NMC). Since cobalt is currently considered as a critical raw material, nickel-rich NMC cathodes are now designed with lower cobalt contents. The synthesis of these new NMC types requires LiOH instead of Li2CO3, which was used for Co-richer NMC materials in the past. Most production routes of LiOH start from Li2CO3 or Li2SO4. However, LiCl could also be a potential precursor for LiOH, as it could be obtained from various lithium sources. A two-step solvent extraction process (SX) was developed for direct conversion of LiCl into LiOH, using a phenol (butylhydroxytoluene or BHT) and a mixture of quaternary ammonium chlorides (Aliquat 336) in an aliphatic diluent (Shellsol D70) as the solvent. The SX process was validated in counter-current mode using a rotary agitated Kühni extraction column. The use of a column instead of mixer-settlers reduced the CO2 uptake by the final product (LiOH), which prevented the partial conversion of LiOH to Li2CO3. A total of 75 L of LiCl feed solution was processed in the Kühni column to obtain a solution of LiOH with a final purity of more than 99.95%, at a yield of 96%.Graphical

Highly efficient diluent-free solvent extraction of uranium using mixtures of protonated trioctylamine and quaternary ammonium salts. Comparative Life Cycle Assessment with the conventional extractant

A more environmentally friendly solvent extraction process was formulated for uranium extraction using diluent-free extractants based on trialkylammonium compounds. The effect of ammonium cations and anions toward extraction efficiency, viscosity and phase separation was also evaluated. These systems were shown to be highly efficient and simple to implement as they rely on the same chemical components as those applied in the actual industrial process. It has also been demonstrated that using such alternatives allows not only to prevent third phase formation and subsequent extractant degradation, but also reduces the evaporation loss of solvent by a factor of 20. Among the systems investigated, the pure [TOAH]2[SO4] was selected as the simplest and most efficient. A comparative Life Cycle Assessment (LCA) was also conducted between this system and the conventional solvent to compare more objectively their sustainability. Results based on four environmental indicators show that the new system is 18 times less impactful. Contrary to expectations, this study also showed that the pure (diluent-free) extractant system needs to be at least 2 times more efficient in terms of metal extraction to become significantly more sustainable. Other main effects contributing to the LCA are derived from: (i) the production of chemicals, which is much more harmful for extractants than for aliphatic diluents, (ii) the loss of Volatile Organic Compounds (VOC) to the environment, and (iii) to a lesser extent, the additional centrifugation step that may be required to separate more viscous systems.

Decomposition of liquid-liquid extraction organic phase structure into critical and pre-peak contributions

Solution nanostructure induced by amphiphile self-association plays an important role in various chemical and physical processes, including liquid-liquid extraction (LLE). Small angle scattering techniques are an essential means of probing this structure, but, due to non-uniqueness of scattering patterns, their interpretation is not trivial. Here, we decompose small angle x-ray scattering (SAXS) patterns for a range of binary LLE organic phases into two components: Ornstein-Zernike and pre-peak contributions resulting from, respectively, critical concentration fluctuations and packing of the amphiphilic extractant molecules in the nonpolar aliphatic diluent. While we previously applied Ornstein-Zernike scattering models to similar organic phases, including the pre-peak explicitly in the fit allows us to measure weak fluctuations at high extractant concentration and simultaneously obtain information on the position and intensity of the correlation peak related to amphiphile packing. Scattering patterns and partial structure factors calculated from molecular dynamics simulations support this interpretation. We demonstrate how this minimal scattering model describes nanostructuring for a large number of extractant types over their entire extractant/diluent composition ranges, suggesting simple and universal behavior. The straightforward assignment of these structural contributions facilitates the comparison of these features between different classes of extractant molecules and will enable further studies of organic phase aggregation. Applicability to more complex, process-relevant organic phases is illustrated with post-contact organic phases containing significant quantities of extracted lanthanide nitrate salt, which we find are readily described by this model.

Separation of americium from highly active raffinates by an innovative variant of the AmSel process based on the ionic liquid Aliquat-336 nitrate

A new variant of the AmSel (Americium Selective Separation) system for the separation of Am(iii) from a PUREX raffinate was tested in which the aliphatic diluent was replaced by the ionic liquid Aliquat-336 nitrate.

Low-carbon footprint diluents in solvent extraction for lithium-ion battery recycling.

This study investigated the influence of the diluent on the extraction properties of three extractants towards cobalt(ii), nickel(ii), manganese(ii), copper(ii), and lithium(i), i.e. Cyanex® 272 (bis-(2,4,4-trimethylpentyl)phosphinic acid), DEHPA (bis-(2-ethyl hexyl)phosphoric acid), and Acorga® M5640 (alkylsalicylaldehyde oxime). The diluents used in the formulation of the extraction solvents are (i) low-odour aliphatic kerosene produced from the petroleum industry (ELIXORE 180, ELIXORE 230, ELIXORE 205 and ISANE IP 175) and (ii) bio-sourced aliphatic diluents (DEV 2138, DEV 2139, DEV 1763, DEV 2160, DEV 2161 and DEV 2063). No influence of the diluent and no co-extraction of lithium(i), nickel(ii), cobalt(ii), manganese(ii) and aluminum were observed during copper(ii) extraction by Acorga M5640. The nature of the diluent influenced more significantly the extraction properties of manganese(ii) by DEHPA as well as cobalt(ii) and nickel(ii) by Cyanex® 272. Life cycle assessment of the diluents shows that the carbon footprints of the investigated diluents followed the following order: (ELIXORE 180, ELIXORE 230, ELIXORE 205) from petroleum industry > kerosene from petroleum industry > diluent produced from tall oil (DEV 2063) > diluents produced from recycled plastic (DEV 2160, DEV 2161) > diluents produced from used cooking oil (DEV 2138, DEV 2139). By taking into account the physicochemical properties of these diluents (viscosity, flashpoint, aromatic content), the extraction properties of Acorga® M5640, DEHPA, Cyanex® 272 in these diluents and the CO2 footprint of the diluents, this study showed DEV2063 and DEV2139 were the best diluents. A low-carbon footprint solvent extraction flowsheet using these diluents was proposed to extract selectively cobalt, nickel, manganese, lithium and copper from NMC black mass of spent lithium-ion batteries.

Conversion of Lithium Chloride into Lithium Hydroxide by Solvent Extraction

A hydrometallurgical process is described for conversion of an aqueous solution of lithium chloride into an aqueous solution of lithium hydroxide via a chloride/hydroxide anion exchange reaction by solvent extraction. The organic phase comprises a quaternary ammonium chloride and a hydrophobic phenol in a diluent. The best results were observed for a mixture of the quaternary ammonium chloride Aliquat 336 and 2,6-di-tert-butylphenol (1:1 molar ratio) in the aliphatic diluent Shellsol D70. The solvent extraction process involves two steps. In the first step, the organic phase is contacted with an aqueous sodium hydroxide solution. The phenol is deprotonated, and a chloride ion is simultaneously transferred to the aqueous phase, leading to in situ formation of a quaternary ammonium phenolate in the organic phase. The organic phase, comprising the quaternary ammonium phenolate, is contacted in the second step with an aqueous lithium chloride solution. This contact converts the phenolate into the corresponding phenol by protonation with water extracted to the organic phase, followed by a transfer of hydroxide ions to the aqueous phase and chloride ions to the organic phase. As a result, the aqueous lithium chloride solution is transformed into a lithium hydroxide solution. The process has been demonstrated in continuous counter-current mode in mixer–settlers. Solid battery-grade lithium hydroxide monohydrate was obtained from the aqueous solution by crystallization or by antisolvent precipitation with isopropanol. The process consumes no chemicals other than sodium hydroxide. No waste is generated, with the exception of an aqueous sodium chloride solution.Graphical

Separation of cobalt and nickel via solvent extraction with Cyanex-272: Batch experiments and comparison of mixer-settlers and an agitated column as contactors for continuous counter-current extraction

The separation of cobalt and nickel was carried out via solvent extraction using the commercial extractant bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex-272). Solvent extraction experiments were performed on a batch scale to optimize the extractant concentration, saponification degree, equilibration time, organic-to-aqueous phase ratio (O/A), and stripping conditions. High selectivity of cobalt over nickel was obtained at an extractant concentration as low as 0.2 M (or 20% v/v), with a saponification degree of 40% and a phase ratio O/A of 1/1. Furthermore, eleven diluents, covering different aliphatic– aromatic compositions were tested to evaluate their effect on the separation of cobalt and nickel. Cobalt extraction efficiencies were not significantly impacted by the nature of the diluent. However, the co-extraction of nickel was approximatively 10% higher when toluene was used as a diluent in comparison with the aliphatic diluent Shell GS270. The process was validated in continuous mode using a battery of mixer-settlers and an agitated Kühni column. High recovery of cobalt and negligible co-extraction of nickel were achieved in both cases. The specificities, advantages, and challenges of the operation of both types of liquid-liquid extraction equipment were further discussed.

Solvometallurgical Process for the Recovery of Tungsten from Scheelite

The industrial state-of-the-art processes to extract tungsten from scheelite (CaWO4) require high pressures and temperatures. These flowsheets consume a large excess of chemicals (which are very hard to recycle) and generate up to 25 tons of high-salinity wastewater per ton of ammonium paratungstate product. In this work, a more sustainable conceptual flowsheet for the recovery of tungsten from high-grade (55.0 wt % W) and medium-grade (3.3 wt % W) scheelite ores was developed at the lab scale. Leaching of CaWO4 was tested in solutions of 37.0 wt % aqueous HCl in organic solvents (ethylene glycol, poly(ethylene glycol) 200, acetonitrile) and ionic liquids (Aliquat 336). The tungstate (HxWyOzn–) generated by the reaction between CaWO4 and HCl was only solubilized in the ethylene glycol system with an appropriate amount of 37.0 wt % aqueous HCl, whereas in all other solvents, it either precipitated or CaWO4 did not dissolve. After the dissolution of tungsten, nonaqueous solvent extraction was used to separate tungsten from calcium, by means of a solvent consisting of 20 vol % Aliquat 336 in the aliphatic diluent GS190 with 10 vol % 1-decanol as a modifier. Scrubbing with water removed the co-extracted iron. Finally, tungsten was recovered as ammonium tungstate (NH4)2WO4, the precursor of ammonium paratungstate, by stripping in a mixture of aqueous ammonia and ammonium chloride. Paratungstate is the most common intermediate for the production of tungsten oxide or tungsten metal. One drawback that needs to be adequately addressed, prior to further upscaling of this conceptual flowsheet, is the potential formation of trace levels of 2-chloroethanol in the leaching stage. It is hypothesized that this problem can be circumvented by further optimizing process conditions to enhance the mass transfer and reduce the reaction time, such as better mixing of the solid and the lixiviant.

Ammoniacal Solvoleaching of Copper from High-Grade Chrysocolla

The copper silicate ore chrysocolla forms a large potential copper resource, which has not yet been fully exploited, due to difficulties associated with its beneficiation by flotation and metallurgical processing. Direct acid leaching of chrysocolla causes silica gel formation. Therefore, in this work, the feasibility of solvometallurgical methods to leach copper from high-grade chrysocolla while avoiding issues with silica gel formation was assessed. Ammoniacal solvoleaching was performed with a solvent comprising the chelating extractant LIX 984 N or the acidic extractant Versatic acid 10 in an aliphatic diluent (ShellSol D70 or GTL Fluid G70), combined with a small volume of aqueous ammonia. In the three-phase system, aqueous ammonia dissolves copper from milled and sieved chrysocolla, while copper is simultaneously extracted to the organic phase, releasing ammonia that can be reused for further extraction. The best results were obtained with LIX 984 N as extractant: using a 50 vol% LIX 984 N solution, about 75% of copper could be extracted after 60 min of leaching at 25 °C. The stripping of copper from the pregnant leach solution was optimized. Quantitative stripping of copper was achieved with 1.89 M sulfuric acid and the final aqueous solution of copper sulfate had a concentration of 33 g L−1. Experiments in a leaching reactor (1 L) and small battery of mixer-settlers (3 stages, 35 and 143 mL effective volume in the mixer and the settler, respectively, per stage) were successfully conducted and allowed to recover copper with a purity of 99.9%. A conceptual flow sheet has been developed.Graphical

Selection criteria of diluents of tri-n-butyl phosphate for recovering neodymium(III) from nitrate solutions

The selection of a proper diluent should be based on several criteria such as the distribution ratio, phase disengagement time, cost, safety and environmental impact of the process. The effect of different diluents on the solvent extraction of Nd(III) by the neutral extractant tri-n-butylphosphate (TBP) from nitrate feed solutions was studied. The nature of the diluent had little effect on the extraction kinetics of Nd(III) by TBP above 2.5min. In general, phase disengagement times were relatively shorter for aromatic diluents compared to aliphatic diluents. Conversely, extraction efficiencies were the highest for aliphatic diluents, slightly lower for mixed aliphatic-aromatic diluents and much lower for aromatic diluents. The poorer extraction efficiencies of aromatic diluents maybe due to the lower concentration of free extractant as a result of the stronger interactions of the diluent with water and/or of the diluent with the extractant. Under the experimental conditions, the differences in extraction between aliphatic and aromatic diluents decreased with increasing the salting-out effect of nitrate ions in the feed. At nitrate concentrations of 4.5molL−1 or more, the different diluents had a limited influence on the metal extraction with 1molL−1 TBP from feed solutions of 1gL−1 Nd(III). Thus, under these conditions, the selection of the diluent can be preferably based on its cost, safety and biodegradability rather than on its physico-chemical properties.

Solvent Extraction Studies for the Separation of Trivalent Actinides from Lanthanides with a Triazole-functionalized 1,10-phenanthroline Extractant

ABSTRACT A new N-atom donor extractant 2,9-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)-1,10-phenanthroline (EH-BTzPhen) was synthesized and used in solvent extraction studies to separate the trivalent minor actinide americium(III) and curium(III) from europium(III), representing fission product lanthanides. The extractant was found to be soluble in 1-octanol and in the Aliquat-336 nitrate ([A336][NO3]) ionic liquid diluent, but insoluble in n-dodecane. The [A336][NO3] is a fully incinerable room temperature ionic liquid, and has a higher flash point than aliphatic diluents such as 1-octanol. The EH-BTzPhen proved to be effective for selective minor actinide extraction only in combination with 2-bromohexanoic acid synergist when 1-octanol was used as a diluent (SF Am/Eu > 200). The change of the diluent from 1-octanol to Aliquat-336 nitrate allowed selective An(III) extraction from low acidity feed solutions without the need of a synergist (SF Am/Eu ~ 70 and SF Am/Cm ~ 1.9–2.2). The phase transfer kinetics of the ligand-metal complexes is however very slow at 22 °C in the case of both solvents. With this newly synthesized extractant, the achieved SF Am/Cm was comparable to the values achieved with the established CyMe4BTBP and CyMe4BTPhen extractants.

Extraction of Np4+ and Pu4+ from nitric acid feeds using three types of tripodal diglycolamide ligands

Studies on the liquid – liquid extraction of Np4+ and Pu4+ were carried out using three tripodal diglycolamide ligands with different centers viz. a carbon atom (termed as C-pivot tripodal DGA or T-DGA), a nitrogen atom (termed as N-pivot tripodal DGA or TREN-DGA) and a benzene centered tripodal diglycolamide (termed as TAETEB) in an aliphatic diluent mixture of n-dodecane (95%) and isodecanol (5%). The extraction efficiency of the ligands followed the trend: TAETEB > T-DGA > TREN-DGA, while Pu4+ was far more efficiently extracted than Np4+. A solvation type extraction mechanism was proposed based on the extraction profiles obtained as a function of the feed nitric acid concentration where the extracted species was found out to be M(NO3)4·nL (where M = Np or Pu and n was in between 1 and 2). The extraction of other relevant metal ions was also investigated which followed the trend: Am3+ > UO22+ ~ NpO22+ > Sr2+ > Cs+. While Am3+ extraction was lower with TREN-DGA as compared to that of Np4+ and Pu4+, the trend being Am3+ < Np4+ < Pu4+, the relative extraction trend changed with the extractants to Np4+ < Am3+ < Pu4+ for T-DGA and to Np4+ < Pu4+ < Am3+ for TAETEB. The radiolytic stability of the extractants showed contrasting behavior with respect to the metal ion extraction. While the solvent containing 1 × 10−3 M solutions of the ligands showed decreased metal ion extraction for T-DGA and TAETEB when exposed to 200 kGy gamma radiation, an opposite trend was seen for TREN-DGA where the metal ion extraction was found to increase by over 2 times. The metal ions were efficiently stripped using a mixture of 0.5 M oxalic acid and 0.5 M nitric acid. Temperature variation studies were carried out to determine the thermodynamic parameters.

Solvent Extraction Separation of La, Sm and Dy from Sulfate-Phosphate Medium by CYANEX 272 in Kerosene

Extraction and separation of La, Sm and Dy ions from acidic sulfate-phosphate solutions was investigated using a cation exchange extractant, bis(2,4,4-trimethylpentyl) phosphinic acid, CYANEX 272, in kerosene. The influence of shaking time, equilibrium pH, extractant, sulfate and phosphate ion concentrations, diluent type and temperature was studied. The extraction was found to be pH-dependent, and increasing the phosphate ion concentration inhibited the extraction which was found to be endothermic. The stoichiometry of the extracted metal species was found to be MOH.H2OHSO4H2A.A2. Aliphatic diluents were found to enhance the extraction compared to aromatic diluents. The results showed that there was a separation mode between the metal ions when varying the hydrogen ion and sulfate ion concentrations, under the used experimental conditions. The investigated process was used for the recovery of La, Sm and Dy from the acid solution resulting from the leaching of low-grade monazite.

Gamma Radiolysis of TODGA and CyMe4BTPhen in the Ionic Liquid Tri-n-Octylmethylammonium Nitrate

ABSTRACTRadiolytic stability of the extractants N,N,N’,N’-tetraoctyl diglycolamide (TODGA) and 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline (CyMe4BTPhen) in the ionic liquid tri-n-octylmethylammonium nitrate ([N1888][NO3]) was studied via the combination of a steady-state irradiation by cobalt-60 gamma-radiation, followed by solvent extraction and identification of radiolysis products by High-Performance Liquid Chromatography coupled to Electro Spray Ionisation Mass Spectrometry (HPLC-ESI-MS). The observed trend for the distribution ratios of trivalent minor actinides and Eu(III) showed a decrease as a function of absorbed dose in the case of the TODGA solvent. The gamma irradiations were conducted in the presence or absence of an acidic aqueous phase. The determined dose constants for TODGA under neutral or acidic conditions were up to four times lower than the values reported in aliphatic diluents under comparable conditions. The degradation patterns were similar to those found by former studies on TODGA diluted in n-dodecane; only de-alkylation and bond ruptures within the diglycolamide core were observed. The presence of an acidic aqueous phase during irradiation resulted in a different relative abundance of certain radiolysis products of both the diluent and TODGA and a higher dose constant compared to the neutral irradiation conditions. A quantification of CyMe4BTPhen in irradiated samples with the [N1888][NO3] diluent was not possible, but the effect on its extraction properties was evaluated. The distribution ratios slightly increased under the effect of absorbed dose, indicating the formation of radiolysis products that are efficient extractants as well.

Solvent extraction of An(III) and Ln(III) using TODGA in aromatic diluents to suppress third phase formation

The extraction of nitric acid, trivalent actinides and lanthanides with N,N,N′,N′-tetra-n-octyl-3-oxapentanediamide (TODGA) dissolved in the aromatic diluents 1,4-diisopropylbenezene and tert-butylbenzene was studied. Nitric acid extraction proceeds along the formation of 1:1 and 2:1 HNO3-TODGA adducts. An(III) and Ln(III) distribution ratios were determined as a function of nitric acid, TODGA and Ln(III) concentrations. Distribution ratios are approximately an order of magnitude lower in aromatic diluents compared to aliphatic diluents. No third phase formation was observed when contacting the solvent with an aqueous phase containing 1.5 mol/L Er(NO3)3 in 2–4.3 mol/L HNO3. Slope analysis indicates the formation of 1:3 and 1:4 M(III):TODGA complexes. Using TRLFS, the formation of a previously unknown 1:2 complex in organic phases loaded with Ln(III) was observed for the first time.

Alkali baking and solvometallurgical leaching of NdFeB magnets

End-of-life NdFeB magnets are an important secondary source of rare-earth elements (REEs) and cobalt. Recycling of these magnets can also mitigate the supply problems of its constituent critical REEs (mainly neodymium and dysprosium). The recycling of bonded NdFeB magnets has received much less attention than that of sintered NdFeB magnets. In this study, a novel flow sheet is presented for recycling of bonded NdFeB magnets that is applicable to sintered magnets as well. Demagnetized magnet powder was mixed with 25 or 40 wt./vol% NaOH solution and baked at 150 to 200 °C for 30 to 540 min. In this way, REE metals were transformed into their corresponding hydroxides, whereas iron metal formed NaFeO2. By washing the reaction mixture with water, 96.5% of Na was recovered as NaOH and Na2CO3, whereas 90.3% of B was recovered as borax. The calcine containing REE hydroxides and iron oxide was then leached at 60 or 90 °C with 20 vol% Versatic Acid 10 diluted in an aliphatic diluent. >95% of the REEs were dissolved, with <1% co-dissolution of iron and <10% co-dissolution of cobalt. Precipitation stripping with an oxalic acid solution quantitatively regenerated the organic solvent with virtually the same composition of fresh solvent. After calcination of the oxalate precipitate, a mixed rare-earth oxide with 98.4 wt% purity was produced. The waste oxalic acid solution (pH ≤1) containing co-dissolved sodium and minor amounts of iron and cobalt could be used as a leaching agent for Co in the maghemite-dominated residue.

Development of a solvometallurgical process for the separation of yttrium and europium by Cyanex 923 from ethylene glycol solutions

Recycling of critical raw materials such as rare-earth elements (REEs) is increasingly crucial in the development of a sustainable economy. Separation of individual REEs (mainly yttrium and europium) from lamp phosphor waste has become essential due to the substantial stockpiling of end-of-life fluorescent lamps. The mutual separation of Y(III) and Eu(III) from aqueous chloride solutions with solvating extractants by conventional extraction methods is highly inefficient. Hence, separation of Y(III) and Eu(III) was investigated using a novel technique called “non-aqueous solvent extraction”. Unlike conventional solvent extraction, the new approach uses two immiscible organic phases (more polar (MP) and less polar (LP)) instead of an aqueous and an organic phase. The present work describes a new solvometallurgical process for the separation of Y(III) and Eu(III) from ethylene glycol solutions using the solvating extractant Cyanex 923 in an aliphatic diluent. This extraction system exhibits improved separation compared to extraction from aqueous solutions. Following predictions based on a McCabe-Thiele diagram, a three-stage counter-current extraction simulation was carried out to extract Y(III) quantitatively, with 7% co-extraction of Eu(III) at a volume phase ratio of MP:LP of 1.5:1. The co-extracted Eu(III) was selectively scrubbed in two stages using an Y(III) scrub solution. Y(III) was recovered from the loaded less polar organic phase by precipitation stripping with an aqueous oxalic acid solution and a subsequent calcination step. Y2O3 with a purity of more than 99.9% was obtained. A complete process flow sheet, comprising extraction, scrubbing and stripping steps for the separation of Y(III) and Eu(III) is reported. The feasibility of the developed process was successfully demonstrated in continuous mode using a battery of mixer-settlers.