Ligands for selective metal ion extraction: A molecular modeling approach

We present a density functional theory (DFT) based study on interaction of alkali metal cations (Li⁺ and Na⁺) with macrocyclic crown ethers of different ring sizes. The minimum energy structures, binding energies, and binding enthalpies of crown ether–cation complexes have been determined with a correlated hybrid density functional, namely Becke’s three-parameter functional, B3LYP using a split valence basis function, 6-311++G(d, p). Geometry optimizations for all the crown ether–cation complexes were carried out with several initial guess structures based on semi-empirical PM3 optimized results. For both metal ions, the calculated values of binding energy and binding enthalpy increase with the increase in size of the crown ether ring, i.e. with the increase in the number of donor oxygen atoms in crown ether. The calculated values of gas phase binding energy for lithium ions are always higher than those for sodium ions in the case of all macrocyclic crown ethers studied at present. The calculated values of binding enthalpy are in good agreement with the reported experimental data.     

The bonding in thiolate protected gold nanoparticles from Au4f photoemission core level shifts

Density functional theory calculations are used to evaluate Au4f core level shifts of methyl thiolate protected Au(25), Au(102) and Au(144) nanoparticles. The shifts are found to provide sensitive fingerprints of the chemical environment. In particular, Au atoms in protective gold-thiolate complexes have higher binding energies than Au atoms with solely metal neighbors. The core level shifts for the nanoparticles are compared to the corresponding results for methyl thiolates adsorbed on Au(111) and implications for the understanding of the gold-sulfur bond is discussed.     

In-Silico Calculations as a Helpful Tool for Designing New Extractants in Liquid-Liquid Extraction

Due to new challenges, new extraction solvents based on innovative extractants are needed in hydrometallurgy for specific tasks. Thus, the aim of the present article is to discuss the potential and limits of Quantitative Structure–Properties Relationship (QSPR) and molecular modeling for identifying new extractants. QSPR methods may have useful applications in such a complex problem as the design of ligands for metal separation. Nevertheless, the degree of reliability of the predictions is still limited and, in the present state of the art, these techniques are likely more useful for optimization within a given family of extractants than to build in-silico new reagents. The molecular modeling techniques provide binding energies between target metals and given ligands, as well as optimized chemical structures of the formed complexes. Thus, in principle, the information, which can be deduced from the molecular modeling computations are richer than that provided by QSPR methods. Nevertheless, an effort should be made to establish more tangible links between the calculated binding energies and the physical parameters used by the hydrometallurgists, such as the complexation constants in aqueous phase (β_MAn) or better the extraction constants (K_ex).     

Nanoparticle decoration of carbon nanotubes by sputtering

Vapor phase growth of gold, nickel and titanium metal nanoparticles on multiwall carbon nanotube (MWCNT) buckypaper by sputtering was investigated. The size and distribution of nanoparticles was dependent on the intrinsic binding energy of the metal elements, but could be altered to mimic that of metals with different binding energies by in situ modification of the MWCNT surfaces by energetic metal ions or annealing of the buckypaper. A range of average gold particle diameters from approximately 5–30 nm could be produced depending on the intrinsic sputter process parameters (especially metal ion flux and kinetic energy) and defect density of the MWCNT surfaces, which could also be controlled by annealing prior to sputtering. The diameter of the MWCNTs had a significant influence on the geometry of the nanoparticles. Particles were elongated along the nanotube axis for tube diameters <30 nm. Remarkably strong alignment of the particles along the nanotube axis was observed, especially for MWCNTs with higher defect densities.     

Synthesis of calix[4]crown‐4 oligomers containing hard and soft ion binding sites

Three calix [4]crown‐4 derivatives and their oligomers, p‐tert‐butylcalix [4]crown‐4 oligomer 5 , p‐tert‐butylcalix [4]dioxacrown‐4 oligomer 6 , p‐tert‐butylcalix [4]diazacrown‐4 oligomer 7 that contain hard and soft ion binding sites, are synthesized to estimate selective extraction of cesium ions from the aqueous to the organic phase. The binding sites may complex alkali metal ions or transition metal ions selectively. Oligomers are fairly good extractants for transition metal ions in comparison with their monomers, which suggests that polyoxyethylene bridges are efficient for complexing metal ions, especially for transition metal ions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and Evaluation of N,N′-dimethyl-N,N′-dicyclohexyl-Malonamide (DMDCMA) as an Extractant for Actinides

A malonamide based extractant, i.e., N,N′-dimethyl-N,N′-dicyclohexyl-malonamide (DMDCMA) was synthesized in a single step and tested for the extraction of several actinide ions such as Am(III), U(VI), Np(IV), Np(VI), Pu(IV), Pu(VI), etc., from nitric acid medium. The extractant was soluble in phenyltrifluoromethylsulphone (PTMS or FS-13) unless stated otherwise. The effect of various experimental parameters, such as the aqueous phase acidity (0.01–3 M HNO₃), nature of the acid, oxidation states of the metal ions, ligand concentration, nature of the diluent and temperature on the extraction behavior of metal ions was studied. The extracted Am(III) species was determined from slope analysis method as [Am(NO₃)₃(DMDCMA)₂]. The extraction of the metal ions was found to increase with the aqueous phase acidity. The temperature variation studies allowed the calculation of the heat of the two-phase extraction reaction as well as the corresponding extraction constants. These studies revealed that DMDCMA showed good extraction for all the actinide metal ions investigated, and have the advantage of single stage synthesis and easier purification protocol.     

Rare Earth Metal Extraction by Liquid Surfactant Membranes Containing a Calixarene Carboxylate Derivative: Permeation Acceleration Effect of Sodium Ions

ABSTRACT

Calixarene carboxylate derivatives were used as a mobile carrier for rare earth permeation in a liquid surfactant membrane (LSM) system. The effect of alkali metal ions on the extraction behavior of rare earth metals in both liquid-liquid extraction and LSM systems has been studied. The addition of sodium ions considerably enhanced the extraction ability of rare earth metals in the extraction equilibrium. Furthermore, the presence of alkali metal ions in the material solution affected the rate of rare earth permeation in LSMs. The most accelerative transport of rare earth metals by LSMs was achieved by the addition of sodium ions. This acceleration effect of sodium ions was predominant in a tetracarboxylate calixarene whose cavity size just fits the ionic diameter of sodium ions. The sodium-loaded calix[4]arene derivative showed good performance as an effective mobile carrier for rare earth metals in the presence of sodium ions.     

Influence of chemical speciation on the separation of metal ions from chelating agents by nanofiltration membranes

The simultaneous separation of various metal ions (nickel, copper, calcium, and iron) from chelating agents (EDTA and citric acid) in water streams using Nanofiltration membranes is analyzed. Assuming that multiply-charged species are highly rejected, chemical speciation computations reproduce the observed patterns of metal and ligand rejection at different pH values and concentrations. The separation of metal ions from citric acid is achieved in acidic conditions, where multiply-charged free metal ions and neutral or singly charged free chelating species are abundant. Overall, speciation studies help to evaluate the applicability of Nanofiltration for recycling chelating agents used for metal extraction.     

Quo vadis Anionenextraktion?

Quo Vadis Anion Extraction? Reactive extraction processes represent efficient and smart technologies for separation and concentration of metal ions in solution. Despite the importance of anions in biology, medicine, environment and industry, practical examples of anion extraction are relatively limited compared to metal ion separation. Anion extraction processes are mainly based on the non‐specific ion‐pair formation with hydrophobic ammonium cations. In these processes the phase transfer of anions is dominated by their lipophilicity. The specific characteristics of anions in comparison to those of cations are closely connected to the difference in extraction processes for the two ion types. Novel approaches for specific binding and selective transport of anionic components are based both on the better understanding of the biological role of anions and on the possibilities of supramolecular chemistry to built up receptor architectures with complementary binding modes for anions. In the given review the authors discuss present research tendencies and application possibilities of new extractant types for separation and concentration of anionic species in solution.     

Where is the Anion Extraction Going?

Reactive extraction processes represent efficient and smart technologies for separation and concentration of metal ions in solution, which are frequently used in industry. Despite the importance of anions in biology, medicine, environment and industry, practical examples of anion extraction are relatively limited compared to metal ion separation. Anion extraction processes are mainly based on the nonspecific ion pair formation with hydrophobic ammonium cations. In this case the phase transfer of anions is dominated by their lipophilicity. The reasons for this situation are closely connected with the specific features of anions in contrast to cations. Novel approaches for specific binding and selective transport of anionic components are based both on the better understanding of the biological role of anions and on the possibilities of supramolecular chemistry to create receptor architectures with complementary binding modes for anions. In the given review the authors discuss present research tendencies and application possibilities of new extractant types for separation and concentration of anionic species in solution.     

Recovery and Separation of Lanthanum(III), Aluminum(III), Cobalt(II), and Nickel(II) from Misch Metal by Solvent Extraction Using Bis(2-ethylhexyl) phosphinic Acid

Abstract

This paper describes use of bis(2-ethylhexyl) phosphinic acid as a reagent for extraction and mutual separation of lanthanum(III), aluminum(II), cobalt(II), and nickel(II) in 1.0 mol/L sodium nitrate. The extraction and stripping behavior of the four metal ions has been investigated using the extractant in Solvesso #150 as a diluent. The mutual separation and recovery of the metal ions from their mixtures has been tested by multistage extraction with a conventional separator funnel. A set of separation schemes has also been proposed for a continuous countercurrent multistage extraction which is comprised of ten extraction stages, four scrubbing stages, and seven stripping stages. Lanthanum(III) and aluminum(III) are coextracted but separated by selective stripping into different concentrations of hydrochloric acid. Cobalt(II) can be extracted with the nickel(II)-preloaded extractant solution, whereas nickel(II) remains in the aqueous phase. The successful separation of these metal ions from a misch metal-simulated sample is presented.     

Probing the Structure, Stability and Hydrogen Adsorption of Lithium Functionalized Isoreticular MOF-5 (Fe, Cu, Co, Ni and Zn) by Density Functional Theory

Li adsorption on isoreticular MOFs with metal Fe, Cu, Co, Ni and Zn was studied using density function theory. Li functionalization shows a considerable structural change associated with a volume change in isoreticular MOF-5 except for the Zn metal center. Hydrogen binding energies on Li functionalized MOFs are seen to be in the range of 0.2 eV, which is the desired value for an ideal reversible storage system. This study has clearly shown that Li doping is possible only in Zn-based MOF-5, which would be better candidate to reversibly store hydrogen.     

X-ray photoelectron study of lanthanide borosilicate glass

The elemental and ionic quantitative analyses of the synthetic lanthanide borosilicate glass (Al-B-Gd-Hf-La-Nd-Pu-Si-Sr-O) are performed using the characteristics of the X-ray photoelectron spectra of the outer-shell and inner-shell electrons in the binding energy range 0–1000 eV. The oxidation states of the metal ions in this glass are determined and correspond to the Al³⁺, La³⁺, Nd³⁺, Gd³⁺, Hf⁴⁺, Pu⁴⁺, Si⁴⁺, and Sr²⁺ ions. Taking into account the binding energies of the O 1s electrons for the glass sample under investigation, the average lengths of metal-oxygen bonds on the surface of the sample are estimated to be 0.191 and 0.176 nm, which correspond to oxygen binding energies of 531.3 and 532,3 eV, respectively.     

Studying Peptide-Metal Ion Complex Structures by Solution-State NMR

Metal chelation can provide structural stability and form reactive centers in metalloproteins. Approximately one third of known protein structures are metalloproteins, and metal binding, or the lack thereof, is often implicated in disease, making it necessary to be able to study these systems in detail. Peptide-metal complexes are both present in nature and can provide a means to focus on the binding region of a protein and control experimental variables to a high degree. Structural studies of peptide complexes with metal ions by nuclear magnetic resonance (NMR) were surveyed for all the essential metal complexes and many non-essential metal complexes. The various methods used to study each metal ion are presented together with examples of recent research. Many of these metal systems have been individually reviewed and this current overview of NMR studies of metallopeptide complexes aims to provide a basis for inspiration from structural studies and methodology applied in the field.     

Hydrogen adsorption on supported cobalt,iron, and nickel

This paper emphasizes concepts and fundamentals relating to the kinetics, energetics, and stoichiometries of adsorption of hydrogen on supported cobalt, iron and nickel, with emphasis on nickel. Relationships between catalyst and adsorption properties and the application of hydrogen chemisorption to the measurement of metal surface areas are discussed. Evidence is presented for nonstoichiometric adsorption of hydrogen on supported metals and the results are interpreted in terms (i) reversibility of adsorption and (ii) interactions of hydrogen with metal oxides present on or near metal crystallites. Contamination of the metal surface by support moieties can cause (i) the appearance of new adsorption states of hydrogen at higher binding energies and (ii) an increase in the adsorption activation energy for hydrogen which can lead to severe kinetic limitations in the adsorption process. Precalcination treatments and promoters such as potassium also cause the appearance of new high temperature adsorption states and significantly increase the adsorption activation energy for hydrogen.     

Removal of Cadmium(II) Ions from Chloride Solutions by Cyanex 301 and Cyanex 302

The main goal of this work was to study and compare the extraction of cadmium(II) ions by the two organophosphorous extractants: Cyanex 301 and Cyanex 302. The effect of different variables influencing the extraction of cadmium(II) ions such as the concentration of acid or metal ion and type of extractant has been investigated. Obtained results from the extraction process were compared with the FT-IR spectra. Results of spectrophotometric analysis confirm the observations of the extraction process, for example, the negative effect of hydrochloric acid on cadmium extraction by Cyanex 302.     

Extraction of Lanthanides(III) by a Mixture of a Malonamide and a Dialkyl Phosphoric Acid

Several hydrometallurgical processes studied in France for lanthanide/minor actinide separation use a combination of DMDOHEMA and HDEHP as extractants. Although these processes have proved to be reliable, the modeling of their extraction properties remains a difficult task due to a lack of knowledge about the behavior of the mixed DMDOHEMA-HDEHP organic phase. In the present work, it was found that the solvent extraction of Ln(III) ions by a mixture of these extractants exhibits a complex behavior involving a synergistic effect at either 1 M HNO₃ or high metal concentration, and an antagonistic effect on extraction of metal traces at higher pH (> 2). To understand these effects, Ln(III) complexes formed after extraction by DMDOHEMA and/or HDEHP were characterized by several spectroscopic techniques (FT-IR, UV-Vis, ESI-MS, TRLIFS). Results suggested formation of DMDOHEMA-HDEHP adducts and ternary mixed complexes involving both extractants and possibly a nitrate ion.     

Binding of heavy metal ions by chemically modified woods

Three chemically modified woods were prepared and used for the binding of heavy metal ions. Wood–polythylenimine composite (wood–PEI) was found to be effective for the adsorption of heavy metal ions such as Hg²⁺, Cu²⁺, and other metal ions which tend to form stable ammine complexes. Adsorption of metal ions on a wood–PEI derivative containing dithiocarbamate group (DTC–wood) was higher than that by wood–PEI. Especially, the reactivity of DTC–wood with Hg²⁺ was quite high and the binding capacity of about 5 mmol/g was easily attainable. The rate of adsorption on these wood-based adsorbents was very high, and adsorption of about 70% of total binding capacity was accomplished in the first 1 h. This may be due to a highly porous structure and a hydrophilic nature of the wood which constitutes the skeleton of the adsorbents. Amidoximated wood (AO–wood) prepared by the reaction of cyanoethylated wood with hydroxylamine showed selective adsorptivity for uranium in sea water. More than 53% of uranium in the sea water used was adsorbed by the AO–wood.     

Magnetic Extraction,Detection, and Isotope Analysis of Metal Ions Using Surface Modified Microspheres for Lab-on-a-Chip Applications

Liquid–liquid extraction and ion-exchange chromatography are efficient methods for sequestration of metal ions, but these methods are poorly suitable for microfluidic miniaturization. Here we examine several methods for rapid extraction, fluorometric detection, and the subsequent isotope analysis of lanthanide ions sequestered on surface modified magnetic microspheres as a versatile platform for chemical manipulation. The assays involve immobilization of a mixed-ligand complex of luminescent lanthanide ions at the surface of polystyrene microspheres. Using the ion-exchange properties of these microspheres, this scheme can be extended to the detection of nonluminescent ions.