2-ethylhexyl Phosphonic Acid Research Articles

Synergistic Ion-pair Extraction and Separation of Trivalent Lanthanoid Ions with 4-Isopropyltropolone and 1,10-Phenanthroline into o-Dichlorobenzene.

The synergistic extraction of trivalent lanthanoid (Ln(III)) ions with 4-isopropyltropolone (Hipt) and 1,10-phenanthroline (phen) in o-dichrolobenzene (DCB) was investigated. The synergistic effect in DCB is more significant than that in toluene, and the polynuclear complexes found in toluene are not formed in DCB. Based on the 3-dimensional equilibrium analysis, the extracted species for La(III), Eu(III), and Lu(III) are found to be ion-pairs, such as Ln(ipt)2phen·ClO4 and Ln(ipt)2(phen)·ClO4 in the presence of NaClO4 as a salt, and the extraction constants of the respective species were determined. The simultaneous extraction of different lanthanoids in the present extraction system was demonstrated. The separation factors between lighter lanthanoids were larger than those with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, an excellent extractant for the separation of lanthanoid ions, in decane.

Characterization of the ALSEP Process at Equilibrium: Speciation and Stoichiometry of the Extracted Complex.

We have determined the identity of the complexes extracted into the ALSEP process solvent from solutions of nitric acid. The ALSEP process is a new solvent extraction separation designed to separate americium and curium from trivalent lanthanides in irradiated nuclear fuel. ALSEP employs a mixture of two extractants, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) and N,N,N′,N′-tetra(2-ethylhexyl)diglycolamide (TEHDGA) in n-dodecane, which makes it difficult to ascertain the nature of the extracted metal complexes. It is often asserted that the weak acid extractant HEH[EHP] does not participate in the extracted complex under ALSEP extraction conditions (2–4 M HNO3). However, the analysis of the Am extraction equilibria, Nd absorption spectra, and Eu fluorescence emission spectra of metal-loaded organic phases argues for the participation of HEH[EHP] in the extracted complex despite the high acidity of the aqueous phases. The extracted complex was determined to contain fully protonated molecules of HEH[EHP] with an overall stoichiometry of M(TEHDGA)2(HEH[EHP])2·3NO3. Computations also demonstrate that replacing one TEHDGA molecule with one (HEH[EHP])2 dimer is likely energetically favorable compared to Eu(TEHDGA)3·3NO3, whether the HEH[EHP] dimer is monodentate or bidentate.

Evolution of Acid-Dependent Am3+ and Eu3+ Organic Coordination Environment: Effects on the Extraction Efficiency.

Coordination of trivalent lanthanide and actinide metal ions by lipophilic diglycolamides and phosphonic acids has been proposed for their separation through extraction from aqueous nitric acid solutions. However, the nature of M3+ coordination complexes in these combined solvent systems is not well understood, resulting in low predictability of their behavior. This work demonstrates that a combination of N,N,N',N'-tetrakis(2-ethylhexyl)diglycolamide (T2EHDGA) and weakly acidic 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) in n-dodecane exhibits a complicated extraction mechanism for Eu3+ and Am3+, which continuously evolves as a function of the aqueous phase acidity. At low aqueous phase nitric acid concentrations, M3+ ions are primarily extracted via exchange of the phosphonic acid proton and coordination with HEH[EHP]. At high aqueous phase nitric acid concentrations, HEH[EHP] remains protonated, and M3+ ions are transported to the organic phase by the coextraction of nitrate anions from the aqueous phase, thus forming complex species with T2EHDGA. At moderate acid regimes, both ligands participate in the coordination of M3+ ions and show a synergistic relationship resulting in considerable enhancement of M3+ transport into the combined solvent system over the simple sum of the individual extractants. The observed synergism is caused by differences in organic phase M3+ speciation and has a significant impact on the performance of the organic solvent. Distribution studies with Eu3+ indicate that nominally two or three T2EHDGA ligands participate in metal extraction in the presence of phosphonic acid, while nominally three diglycolamide ligands participate in the presence or absence of phosphonic acid. While synergistic behavior has been observed in many solvent-extraction processes, this system demonstrates a clear correlation between the continuously changing organic speciation of M3+ and its transport into the organic solvent. This paper reports the spectroscopic characterization of the organic phase M3+ species by IR, X-ray absorption, and visible spectroscopies. Spectroscopic evidence indicates a mixed-ligand complex, i.e., a ternary complex at the moderate acid regime, where the greatest degree of synergism is observed. Differences in synergistic extraction of Am3+ and Eu3+ at the low acid regime were observed, indicating their dissimilar extraction behavior.

Separation of gadolinium and europium from chloride media by the solvent extraction technique

Abstract Obtaining rare earth elements (REE) is a complicated task, due mainly to the difficulty of separating and purifying them. Solvent extraction is the most widely used technique for separating REE, and the most common extractants used are organophosphorus acids. The low selectivity of this technique leads to the need for a high number of extraction cells. To increase the selectivity and separation and avoid the practice of saponification of the extractant, the use of complexing agents has been studied, such as low-molecular-weight and biodegradable weak organic acids. The objective of this research was to study the separation of the rare earth elements Gd and Eu by the solvent extraction technique using the organophosphonic extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507). Assays were performed using non-saponified and saponified P507 extractant and adding lactic acid to the aqueous phase prior to extraction. Experimental factorial planning was used to study the effect on the extraction and separation of the Eu and Gd of the variables extractant concentration, initial feed pH, saponification degree, and lactic acid concentration. The greatest Gd extractions were obtained when lactic acid was added to the feed solution. Also, saponification of the extractant and lactic acid addition improved the Gd/Eu separation. The number of stages required to extract Gd using McCabe-Thiele diagrams was estimated, whether or not the solution was conditioned with lactic acid. The largest extraction percentage was obtained by adding lactic acid in a continuous counter-current extraction assay, achieving 94% Gd extraction.

Separation of heavy rare earths by di-(2-ethylhexyl) phosphinic acid: From fundamentals to cascade extraction simulation

Incomplete stripping and high acidity consumption were the major drawbacks for the separation of heavy rare earth elements (HREEs) by the popular extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507). This article studied di-(2-ethylhexyl) phosphinic acid (P227) from thermodynamics and kinetics theoretical researches to cascade extraction simulations for the separation of HREEs. P227 was capable of complete stripping for HREEs with low acidity, and had high organic REE loading with clear and fast phase separation. Constant interfacial area cell with laminar flow was implemented to reveal the different kinetics mechanisms for the extraction and stripping of Lu3+. The multi-stages of cascade extraction simulation designed for the separation between Er3+/Tm3+ could be of great significance for practical application. Corresponding products with high purity at both exits obtained successfully via the simulation. All these will provide the promising industrial applications of P227 with more fundamental data and guidance.

Extraction of chromium (III) from aqueous waste solution in a novel rotor-stator spinning disc reactor

In this work, the removal of chromium (III) from aqueous waste solution by solvent extraction with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl (P507) as extractant is investigated in a novel rotor-stator spinning disc reactor. The effect of rotational speed, volumetric flow rate and rotor-stator distance on extraction efficiency and volumetric mass transfer coefficient are studied. Experimental results indicates that the maximum values of extraction efficiency and volumetric mass transfer coefficient are 97.2 % and 0.40 1/s, respectively. The mass transfer performance inside the rotor-stator spinning disc reactor exceeds that of conventional reactors. Moreover, it is found that the extraction efficiency increases with the increase of rotational speed but with the decrease of volumetric flow rate and rotor-stator distance. The Volumetric mass transfer coefficient increases as both the rotational speed and volumetric flow rate increase, but decreases with the increase of rotor-stator distance. Furthermore, an analysis on the relationships between volumetric mass transfer coefficient and various parameters is launched by the grey correlation method. The calculation result shows good coincidence with the experimental data.

Solvent extraction and molecular modeling studies of Dy(III) using acidic extractants

Abstract In the present work, solvent extraction of Dy(III) from chloride solutions using 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) and Cyanex 572 (a mixture of phosphonic and phosphinic acid extractants) diluted in kerosene has been reported. Pourbaix and speciation diagrams were plotted to understand the chemistry and formation of different species of Dy(III) in chloride solutions. The effects of different extraction parameters such as pH (1–5), extractant concentration (1–60 mM) and chloride concentration (0.05–1 M) were investigated. PC88A was found to extract Dy(III) ions better than Cyanex 572 under similar conditions. Experimental results showed that Dy(III) extraction reaction occurred via a cation exchange mechanism, which was further supported by Fourier-transform infrared spectroscopy (FTIR) studies of organic solutions loaded with Dy(III). Separation studies of Dy(III) from a mixed solution of 16 rare earth elements (REEs) indicate that PC88A works better for light REEs/Dy separation while selectivity of middle and heavy REEs over Dy(III) are superior with Cyanex 572. Molecular modeling was employed to calculate the Gibbs energies of Dy ions in aqueous and organic phases (consisting of phosphonic acid in heptane), which supported the experimental results.

Role of extractants and diluents in recovery of rare earths from waste materials

It is perceived that our society is heading towards an ultra-connected world with the help of emerging technologies. The swift frequency of technological development has been possible due to enhanced advances in IT, cheapness of raw materials that lead to industrial development. Rare earth elements are playing a key role in the economic progress having diverse applications in alloys, magnets, catalyst, phosphors and are utilized in equipments such as batteries, sensors, electric vehicles. The prominence of these elements has gone up due to high demand, limited supply and non-availability of appropriate substitutes. Considering the present scenario, recovery of rare earths from end of life products through economical technology have become top priorities in metallurgy. There are diverse routes to recover rare earths from secondary resources ranging from hydrometallurgical to pyrometallurgical processes. Hydrometallurgical technique such as solvent extraction has been proved beneficial in recovering rare earths from these secondary resources. This review has been framed to discuss the role of extracting agents and diluents in the extraction circuits used for rare earth extraction and separation studies taking into consideration the end of life products. The function of different extractants such as di-(2-ethylhexyl) phosphoric acid (D2EHPA), 2-ethylhexyl phosphonic acid mono-2-ethylhexylester (PC 88A), bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272), trialkyl phosphine oxides (Cyanex 923) and diluents like pentane, hexane, Solvent 70, dodecane, Octanol and cyclohexanone employed for the extraction of rare earths from the waste materials, particularly magnet scraps, spent batteries and lamp phosphors have been highlighted. The recent challenges concerning the development of cost effective, eco-friendly green extractants like tricaprylmethyl ammonium chloride (Aliquat 336), DEHPA· Alamine 336 IL have also been discussed.

Effect of pKa of organophosphorus acidic extractants on the aggregation behavior of diglycolamide in n-dodecane

To understand the role of pKa of the organophsophorus acidic extractant on the reverse micellar aggregation behavior of the binary solution containing tetra-(2-ethylhexyl)diglycolamide (TEHDGA) + acidic extractant in n-dodecane, the extraction behavior of nitric acid and Nd(III) in the binary solution was studied. The acidic extractants chosen were bis(2,4,4-trimethylpentyl)phosphinic acid (CYANEX-272), bis(2-ethylhexyl)phosphonic acid (PC88A) and bis(2-ethylhexyl)phosphoric acid (HDEHP). The results revealed that the acidic extractant with lower pKa produced aggregates of smaller size, and therefore, the binary solution containing TEHDGA and HDEHP in n-DD was identified as the promising solvent for the extraction of trivalent metal ions from nuclear waste.

Dynamic and Solvation Behaviors of ALSEP Organic Ligands.

The Actinide-Lanthanide Separation Process (ALSEP) is a solvent extraction approach for separating relevant trivalent minor actinides (e.g., americium and curium) from used nuclear fuel. However, relatively slow kinetics in the stripping step of the process restricts process throughput when scaled for industrial implementation. To assist in identifying specific kinetic barriers associated with the separation, the solvation and dynamic behaviors of the two organic extractants in the current ALSEP implementation, N,N,N',N'-tetra(2-ethylhexyl)diglycolamide (T2EHDGA) and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEHEHP), were probed through molecular dynamics (MD) simulations. The simulations examined the effects of extractant and nitric acid concentration on the interfacial behavior of the extractants in three solvent systems (n-dodecane, water, and n-dodecane + water). Solvation analyses of T2EHDGA revealed expected amphiphilic behavior in pure solvent systems. In a nitric-acid-free biphasic solvent, it was found that T2EHDGA expressed similar interfacial conformations as HEHEHP, suggesting that a parallel-like configuration, relative to the interface, is adopted at low concentrations. When HNO3 was introduced to biphasic systems containing a single molecule of extractant, HEHEHP was observed to retain a relatively parallel orientation while the T2EHDGA orientation was no longer affected by the presence of the interface. At bulk extractant concentrations, representative of the ALSEP process, the presence of nitric acid had minimal impact on the ligand orientation. Calculated diffusion constants showed that only some systems involving T2EHDGA were affected by the presence of acid.

Extraction of rare earths by undiluted [P666,14][NO3] and DEHEHP, and the recovery of rare earths from lamp phosphors

Ionic liquids (ILs) have been extensively used for separation. However, most of the current reported undiluted IL-based extraction systems still suffer some issues, such as, the heavy loss and a slower extraction kinetic. In this work, the extraction of rare earths (REs) by IL mixture of trihexyl(tetradecyl)phosphonium nitrate ([P666,14][NO3]) and the commercial extractant di(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP), abbreviated as PND, has been investigated. The addition of DEHEHP into IL [P666,14][NO3] not only decreases the viscosity of IL phase, but also produces an obvious synergistic effect. The synergistic enhancement coefficients (R) and the separation factors (αLu/M) between Lu(III) and non-REs for PND were compared with the other two systems: [A336][NO3] (tricaprylmethylammonium nitrate)–DEHEHP (AND) and [P666,14][Cl] (trihexyl(tetradecyl)phosphonium chloride)–DEHEHP (PClD). In addition, αLu/M of PND has also been compared to the conventional P507-kerosene (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester). Finally, PND was used to recover REs from the real feeding of fluorescent lamp phosphors and the extraction parameters have been optimized. It can be concluded that the prominent extraction ability of REs and higher αLu/M of PND make it to be greatly suitable to recover REs from REs-containing secondary resources, such as the waste fluorescent lamp phosphors.

The Effect of Organic Diluent on the Extraction of Eu(III) by HEH[EHP

ABSTRACTBecause there are fewer tools available to probe the interactions therein, the effect of the fundamental chemistry of the organic diluent on solvent extraction equilibria has been under-characterized relative to the aqueous. As a result, diluents for solvent extraction are often selected for an application not for their utility as a medium for reaction, but for other (often equally) important reasons (like low flammability). To begin to improve this imbalance in the science, twenty different diluents have been used in a study of the extraction of radiotracer 152/154Eu3+ from dilute nitric acid solutions using the extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]). To increase the utility of the study and to honor the memory of Professor Jan Rydberg, this investigation was conducted by a cadre of comparatively inexperienced separation scientists (who are as a result no longer inexperienced separation scientists) as a radioanalytical chemistry and solvent extraction educational exercise. Slope analysis was used to determine the apparent stoichiometry of the extracted metal complex. The results discussed in the following indicate that, while the pH dependence exhibits the expected three H+ exchanged per metal ion extracted, the extractant dependence suggests that the number of protonated extractant molecules in the extracted complex changes with the organic diluent. The experimentally observed “extractant dependency” ranges from 2.5 to 3.0 dimer equivalent molecules per extracted metal ion. Ironically, in the diluents exhibiting the highest apparent M:(HA)3 stoichiometry, HEH[EHP] extracts Eu3+ less efficiently. Europium luminescence spectroscopy was used to probe for changes in the first coordination sphere of the complex in different diluents. A model and conceptual framework for understanding these observations is described.

Application of P507 and isooctanol extraction system in recovery of scandium from simulated red mud leach solution

The current recovery technique of Sc was complicated and the chemical consumption was high. This was due to the low content of Sc in resources and the difficulty of stripping. In this research, the isooctanol was added into the 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507) extraction system to reduce the extraction and improve the stripping of Sc. The maximum stripping ratio of Sc from loaded organic phase by sulfuric acid can increase from 10% (without isooctanol) to 99% (with 15 vol% isooctanol). In the extraction test of the simulated red mud leaching liquor, the separation factors between Sc and Zr, Sc and Ti are 36 and 350, separately. At the same time, other metals are almost not extracted. The high selectivity and stripping of Sc suggest that the P507 with isooctanol extraction system can be applied in the practical Sc recovery process.

A comparative study of the solvent extraction of lanthanum(III) from different acid solutions

ABSTRACT Solvent extraction of lanthanum(III) using the organic extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexylester (PC88A) diluted in kerosene from three different aqueous media (sulfuric, nitric and chloride) was investigated. Eh-pH and speciation diagrams suggested that free lanthanum ion (La(III)) species predominate under the experimental conditions studied in this paper. The effects of several parameters on the extraction of lanthanum including initial pH (1.5–7), initial La(III) concentration (0.08–1.35 mmol/L), PC88A concentration (10–90 mmol/L) and temperature (25–55°C) were evaluated. In general, both hydrochloric and nitric acids were found to be more effective than sulfuric acid in terms of higher extraction of lanthanum. The stoichiometry of the extraction reaction and also the equilibrium constant were calculated. The extraction of La(III) was significantly enhanced by increasing pH and PC88A concentration and was only slightly increased by increasing temperature. Stripping studies showed that 1 mol/L acid concentration is adequate for effective stripping of lanthanum from the loaded organic. The stoichiometry of the extraction reaction was also investigated using density functional calculations and found to be in reasonable agreement with the experimental results.

Magnesium Removal from Concentrated Nickel Solution by Solvent Extraction Using Cyanex 272

The refinery of mixed hydroxide precipitate (MHP) from nickel laterite processing by acidic re-leaching will generate a concentrated nickel solution containing some magnesium difficult to remove. Fluorite precipitation method is often used for nickel purification from magnesium contamination, causing serious risk of environmental pollution. Solvent extraction technology has obvious advantages in metal separation and purification which has been widely used in nickel cobalt industries. Magnesium separation from nickel in a synthetic re-leach solution by solvent extraction using Cyanex 272 (bis (2, 4, 4-trimethylpentyl) phosphinic acid)) and its analogue of P 507 (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) was studied. It was found that the separation factor of magnesium over nickel reached higher than 200 at pH 5.5, which is much better than that of P507 with the maximum separation factor of 88 at pH 5.0. The conditions including equilibrium pH, organic concentration and A/O ratio for metal extraction and separation of Mg and Ca from nickel with Cyanex 272 in a concentrated synthetic nickel solution were optimized. A five-stage counter-current batch continuous test was carried out with Cyanex 272 under optimized conditions. More than 99% of the magnesium was removed from the synthetic solution containing 3.4 g/L Mg and 106 g/L Ni using 0.5 M Cyanex 272, leaving only 38 mg/L Mg in the purified nickel solution, which is suitable for the electrowinning.

Differential Stabilization of the Metal–Ligand Complexes between Organic and Aqueous Phases Drives the Selectivity of Phosphoric Acid Ligands toward Heavier Rare Earth Elements

Rare earth elements (REEs) are widely used in several electrical and electronic devices and emerging technologies. With increase in demand of REEs, their recovery from electronic wastes, through hydrometallurgical routes, is a promising alternate source of these elements over conventional mining processes. In a number of experiments, organophosphoric acid ligands such as bis-2-ethylhexyl phosphoric acid (D2EHPA) and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHEHPA) have shown high selectivity toward heavier REEs. While the general extraction equilibrium is well established, an atomistically detailed understanding of the origin of this selectivity is still lacking. We use molecular dynamics simulations to elucidate the structure of the Nd- and Dy-D2EPHA complexes in vacuum, aqueous, and organic phases and show that the selectivity of D2EHPA for Dy arises from the favorable differential stabilization of the complex in the solvent phases, caused by the structural features of the Dy-D2EHPA complex....

Liquid–Liquid Extraction of Yttrium(III) Using 2-Ethylhexyl Phosphonic Acid Mono-2-ethylhexyl (EHEHPA) in a Microreactor: A Comparative Study

Experiments were carried out in a slug flow microreactor to systematically investigate reaction behavior under variation of flow rate, and a comparative study was made. Y-junction microreactor and T-junction microreactor have been used to extract yttrium(III) using 2-ethylhexyl phosphonic acid mono-2-ethylhexyl (EHEHPA or P507). Results show that the maximum extraction efficiency of 90.4% in both microreactors could be achieved corresponding to the minimum flow rate of 10 and 100 μL/min. The values of specific interfacial area remain unchanged with the increase of flow rate, and the specific interfacial area of the Y-junction serpentine microreactor is much higher than that of the T-junction microreactor. Maximum values of volumetric mass-transfer coefficient (1.642 s–1) in the Y-junction microreactor are found to be several orders of magnitude higher than those of the T-junction microchannel (0.043 s–1) and conventional extractors (0.0197 s–1).

Nano ZrO2 Synthesis by Extraction of Zr(IV) from ZrO(NO3)2 by PC88A, and Determination of Extraction Impurities by ICP-MS

High purity Zirconium (Zr) materials are essential in many components of nuclear reactors, especially fuel cladding tubes. Due to the matrix influence, determination of impurities in the Zr materials requires separation from the Zr matrix. Among extraction methods, solvent extraction is common and suitable for large-scale production. In this study, extraction capability of Zr(IV) by 2-ethylhexyl phosphonic acid mono 2-ethylhexyl ester (PC88A) was examined by FT-IR and UV of ZrO(NO3)2 salt, PC88A-toluene solvent, and Zr-PC88A-toluene complex. ZrO2 (obtained from Institute for Technology of Radioactive and Rare Elements—ITRRE), after being separated from the Zr matrix, was determined for impurities using internal standard (indium, In) by 50% of PC88A dissolved in toluene. Separation of impurities from the Zr matrix underwent two stages. First, one cycle of extraction of the Zr matrix and impurities in 3 M HNO3 using 50% PC88A/toluene was conducted. Second, impurities were scrubbed by 4 M HNO3 in two cycles. Results revealed that approximately 74% of Zr(IV) was separated to the organic phase and 26% remained in the aqueous phase. Determination of impurities after separation from the Zr matrix by ICP-MS using internal standard in revealed that the recovery of impurities achieved 95–100%. With the mentioned amount of Zr, the effect of the Zr matrix on the determination of elements by ICP-MS is negligible. Levels of impurities have relative standard deviations (RSD) of less than 6.9% and recovery of 88.6–98.8%. Therefore, the determination of impurities has high reliability and accuracy. The back-extraction of Zr(IV) in organic phase by 1 M H2SO4 has stripped about 99.5% of the Zr matrix back to the aqueous phase. Following this, NH3 was added to the solution containing Zr after back-extraction to form Zr(OH)4 which was then desiccated to produce ZrO2. X-ray Diffraction (XRD), Scanning and Transmission Electron Microscopy (SEM and TEM) images showed that the new ZrO2 product has spherical nanostructure with diameters of less than 25 nm, which is suitable for applications for the treatment of colorants, metal ions in wastewater sources and manufacture of anti-corrosion steel. In addition, the energy dispersive X-ray (EDX) of the new ZrO2 product showed that it has high purity.

Selective Extraction of Scandium by a Long Alkyl Chain Carboxylic Acid/Organophosphonic Ester Binary Extractant

ABSTRACTThe organophosphorus extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) is widely used for solvent extraction of rare earth elements in an acidic leaching solution, but stripping of the loaded metals is difficult because of the high affinity between the metals and the extractant. Adding 100 times the concentration of neodecanoic acid (Versatic 10) to the extractant solution reduces the extraction ability for scandium (Sc) and enables quantitative stripping of the loaded Sc with a mild acidic solution, such as a 1 M mineral acid. The loading capacity is dependent on the PC88A concentration, so PC88A is the main species responsible for Sc extraction in the binary mixture. Nuclear magnetic resonance spectroscopy (NMR) of the organic phases suggests a potential interaction between the mixed extractants through the change in the hydrogen bonding. This causes an antagonistic effect and facilitates efficient Sc stripping from the extractant solution, so this method could be used for scandium recovery in industry.

Synthesis of Phosphonic Acid Ligands for Nanocrystal Surface Functionalization and Solution Processed Memristors

Here, we synthesized 2-ethylhexyl, 2-hexyldecyl, 2-[2-(2-methoxyethoxy)ethoxy]ethyl, oleyl, and n-octadecyl phosphonic acid and used them to functionalize CdSe and HfO2 nanocrystals. In contrast to branched carboxylic acids, postsynthetic surface functionalization of CdSe and HfO2 nanocrystals was readily achieved with branched phosphonic acids. Phosphonic acid capped HfO2 nanocrystals were subsequently evaluated as memristors using conductive atomic force microscopy. We found that 2-ethylhexyl phosphonic acid is a superior ligand, combining a high colloidal stability with a compact ligand shell that results in a record-low operating voltage that is promising for application in flexible electronics.