Marc Hebrant

EFFECT OF NITRIC ACID EXTRACTION ON PHASE BEHAVIOR, MICROSTRUCTURE AND INTERACTIONS BETWEEN PRIMARY AGGREGATES IN THE SYSTEM DIMETHYLDIBUTYLTETRADECYLMALONAMIDE (DMDBTDMA) / n-DODECANE / WATER: A PHASE ANALYSIS AND SMALL ANGLE X-RAY SCATTERING (SAXS) CHARACTERISATION STUDY

ABSTRACT Among the different problems to be solved when designing a liquid-liquid solvent extraction process, third phase formation. i.e. the splitting of the organic phase into two layers when extracting high concentration of solutes, like nitric acid or metallic nitrates (here trivalent f ions), is one of the most important to address. In some conditions the formation of a “third phase” is observed with dimethyldibutyltetradecylmalonamide (DMDBTDMA), a potential extractant used in the DIAMEX process We have investigated the phase behavior of the system DMDBTDMA / n-dodecane / water / HNO3, in the acceptable concentration limits for the DIAMEX process.

Comparison of micellar ultrafiltration and solvent extraction for the removal of copper ions from aqueous solutions

Abstract This paper reports for the first time a systematic comparison between two methods which can be used to remove metal ions from aqueous solutions, namely solvent extraction and micellar extraction coupled with ultrafiltration. Different lipophilic complexing agents have been considered, which were either solubilized in an organic solvent (isooctane or chloroform) or in cationic (CTAB) or non-ionic (C 12 EO 6 ) micelles: 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline (C 11 –HQ, the active compound in the industrial extractant Kelex 100) and 6-[(alkylamino) methyl]-2-(hydroxymethyl) pyridines (C n NHMePyr with n =12 and 16). The yield of extraction Y of copper was measured in the different systems, keeping the conditions as close as possible in terms of amount of extractant used, concentration of metal ions and pH. A theoretical model was developed to predict the curves Y = f (pH), from which the type and stoichiometry of the complexes formed have been proposed. When cationic micelles were considered in ultrafiltration, it turned out that the ion expulsion effect due to Donnan equilibria could not be neglected. A quantitative treatment of this effect is proposed, which leads to quite a nice prediction of the observed data. The results obtained, which also take into account the phase volume effect, demonstrate that when the volume ratios organic/aqueous or micellar pseudophase/aqueous pseudophase have similar values the two extraction techniques considered are almost equally efficient. Micellar extraction appears to be more efficient when compared with biphasic extraction with 1/1 volume ratio.

Micellar extraction of europium (III) by a bolaform extractant and parent compounds derived from 5-pyrazolone

Abstract Micellar ultrafiltration is used to determine the extraction of europium (III) by a series of micelle-solubilized extractants derived from 5-pyrazolone. The extractants, solubilized in CTAB (cetyltrimethylammonium bromide) micelles, have either a single complexing site: 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (HPMBP), 1-phenyl-3-methyl-4-lauroyl-5-pyrazolone (HPMLP) or they are bis-ligands which can be called ‘bolaform’ extractants: 1,6-bis(1′-phenyl-3′-methyl-5′-pyrazolone-4′-)-1,6-hexanedione (HP-4-PH), 1,12-bis(1′-phenyl-3′-methyl-5′-pyrazolone-4′-)-1,12-dodecanedione (HP-10-PH). The yield of extraction is measured as a function of the pH and of the extractant/metal ratio. The efficiencies of the extractants are in the order HP-10-PH>HPMLP>HPMBP and the complex stabilities are larger than in standard solvent extraction, the former ligand giving a yield of europium extraction close to 100% at pH 2. A theoretical model is used to determine the stoichiometries of the extracted complexes, which are then compared with the situations encountered in standard solvent extraction. For the single site complexing agents the complexes formed involved three ligand molecules (L) for one metal. For the bolaform extractants the complex stoichiometries are found to be either EuL 2 H (case of HP-4-PH) or Eu 2 L 3 (case of HP-10-PH). The stoichiometries and stabilities of the complexes are discussed in relation with the confinement effect offered by the micellar particles and the effect of the local concentrations. The association of a CTA + surfactant molecule to the complex, which was suggested by previous works to ensure neutrality, appears here to be unlikely.

Partitioning of homologous complexing agents with varying HLB between water and cationic or nonionic micelles

Abstract A great deal of work is being done at present for better understanding the nature of the mechanisms (interfacial or bulk) involved in the liquid—liquid extraction of metal ions. Micellar systems can be used to mimic the part played by the organic phase. The study reported here is concerned with the partitioning of homologous extractants bearing alkyl chains of varying lengths (from C 4 to C 16 ) between water and micelles. A microdialysis technique was used to determine the binding constants to nonionic (C 12 EO 6 ) and cationic (CTAB) micelles for the neutral and ionized forms of the complexing agents. The data have been analyzed in terms of the free energies of transfer from the aqueous phase to the micellar environments. They indicate that the contribution of a methylene group to the free energy change is −2.4(±0.2) kJ·mol −1 . From a comparison of the data obtained with charged and uncharged extractants and micelles, respectively, the surface potential of the CTAB micelles was estimated to be of the order of +103 mV. Finally, the implications for the p K a s of protonation in the micellar environments are examined.

AOT reversed micelles as carriers of amino acids across liquid membranes. Search for selectivity and chirality effect

Abstract Reversed micelles of diethylhexyl sodium sulphosuccinate (AOT) are used in this work as mobile carriers to transport amino acids between a source (S) and a receiving (R) aqueous phase across an organic liquid membrane (M) (isooctane). For most experiments the aqueous and organic phases were those of a pre-equilibrated Winsor II system. Semipermeable membranes have been introduced between the S and M phases as well as between the M and R phases for technical reasons. The rates of transport of p -iodophenylalanine and tryptophan were compared and discussed in relation to their partition coefficients between water and the AOT palisade layer, showing completely different behaviour between the two amino acids. As the selectivity of the transport process may depend on the water content of the membrane phase and also on the carrier/solute interactions, we have investigated the rate of water uptake by the AOT reversed micelles as well as the influence of the ionization state of amino acids. The last part of the work is concerned with an attempt to perform enantioselective transports using chiral AOT. The analysis of the receiving phase required in that case a chromatographic resolution of amino acid enantiomers. This resolution was affected by the nature of the background salt, which had to be specifically adapted for this purpose. The failure of these experiments in producing enantiomeric enrichments suggests that the rigidity of the surfactant film is not sufficient to permit chiral recognition in that case.

Copper Extraction Kinetics by Beta-Diketone Derivatives (Acylpyrazolones and Acylisoxazolones) in Water/Chloroform Biphasic System

Abstract Copper(II) extraction and back-extraction rates were determined in a water/chloroform system using a bell-shaped transport cell. Various 1-phenyl-3-methyl-4-acyl-pyrazol-5-ones (with acyl = benzoyl, 2-thenoyl, octadecanoyl, p-tert-butylbenzoyl, 3-phenyl-propanoyl, and iso-nonanoyl) and 3-phenyl-4-acylisoxazol-5-ones (with acyl = benzoyl and p-tert-butylbenzoyl) were considered. The back-extraction rate is shown to be limited by the diffusion of the complex in the organic unstirred layer, whatever the stirring speed and whatever the ligand considered. At low stirring speed, the extraction rate appears to be limited by the diffusion of either a complex or a ligand species in the unstirred layers, depending on the pH. At high stirring speed, the extraction rate is limited by the interfacial complexation. The extraction rate dependence on side-group variation cannot be correlated with hydrophobicity or acidity of the extractants and may be explained by structural differences of the CO vicinal group of the acyl.

Kinetics of complexation of metal ions by extractants solubilized in aqueous micellar solutions of cetyltrimethylammonium salts: Effect of the surfactant counterion

Abstract Several experiments have demonstrated that the complexation of metal ions by lipophilic extractants solubilized in cationic micelles does occur, although the electrostatic repulsions between the positively charged surface of the micelles and the metal ions are not favourable for the reaction to proceed. Owing to the very high concentration of anion X − which exists close to the micelle surface one may wonder about the possible contribution in this process of species of the type [MX 4 ] 2− . This problem is addressed here by comparing the kinetics of complexation of four metal extractant couples in different CTA + X − micelles where X − = Br − , Cl − or NO − 3 . The existence of anionic metal species is assumed to be less probable with nitrate than with chloride or bromide. The results definitely show a different behaviour in the presence of nitrate when the extractant is known to be strongly partitioned in the micellar pseudophase, but no counterion effect is detected when less hydrophobic complexing agents are considered. These observations further substantiate the distinction previously made between interfacial complex formation reaction and bulk reaction, this being a function of the extractant hydrophobicity.

Kinetics and mechanism of biphasic transfer of salted water from an aqueous phase to AOT reverse micelles

Abstract The transfer of salted water from an external aqueous phase to AOT reverse micelles is studied in relation with the change of properties from a percolating to a non percolating state of the micelles. A membrane-separated two-compartment cell was used to measure the transfer of salt which was followed by conductivity measurements. We expected a sharp conductivity drop which could have been used as a kind of sensor to detect a threshold of salinity. In fact, this sharp drop was not observed and this is shown to be due to the fact that no excess water is incorporated in the microemulsion phase in these conditions. For this purpose separate analysis of the water and salt incorporated in the microemulsion phase versus time has been performed. Under the conditions used the increase of the salt content is accompanied by a decrease of the water content, even though the initial system was far from being saturated with water. The results are discussed in terms of the different possible mechanisms. Molecular diffusion of water appears to be unlikely and its expulsion can be simply explained by the shrinkage of the microdroplets merging with the interfacial film, this being associated with the electrostatic shielding of the polar head repulsions.

Chemistry for Environmental Scientists. By Detlev Möller. De Gruyter, 2015. Paperback, Pp. XIV+380. Price EUR 69.95, USD 98.00, GBP 52.99. ISBN 9783110409994.

As indicated by its title, the book ‘Chemistry for Environmental Scientists’ aims at covering a very broad field of knowledge. After a short and general introduction, it is divided in four chapters, namely ‘Chemistry under environmental conditions’, ‘Fundamentals of physical chemistry’, ‘Chemistry of the elements and its [sic] compounds in the environment’ and ‘Chemical processes in the environment’. The first chapter gives mainly basic physicochemical concepts on matter and its states. Some examples relating to air, atmosphere, ‘water and waters’ (i.e. pure water and natural waters), soils and dusts are given. The second chapter concentrates on physical chemistry, thermodynamics and kinetics, though the discussed concepts of general chemistry are those usually taught at the bachelor degree level in chemistry. This second chapter is completely independent of the others. The third chapter deals with chemistry in the atmosphere and in the condensed phases of H, O, N, S, C, halogens, phosphorus, metal and metalloids. The final chapter deals with numerous subjects, such as chemical evolution, the formation of the earth, volcanism, photosynthesis, atmospheric chemistry and radioactivity. Although this book deals with a very interesting field of science, it is difficult for me to recommend it. Indeed, the way the species are written is not in the way recommended by the International Union of Pure and Applied Chemistry (IUPAC) and in many cases I simply could not understand the things that were written. [What are the species H and OH in solution? I would have said before (and after) reading this book that they don’t exist in the terrestrial environment. H and OH are only two examples of improbable species among numerous others in the book.] Equilibrium constants are also not calculated as recommended by IUPAC and the chemical activity concept is clearly not considered. What I would understand as radical species are not indicated in the normal way (i.e. with a superscript dot) in most cases, so it is hard to understand the species in question. Moreover, there are some typographical errors which are offputting (for instance, Mg is not the reduced species of Mg). There might be some useful information in this book but the problems described in the preceding paragraph make the reader wary of placing undue reliance on its content. ISSN 2053-2296

Micellar extraction of amino acids using chiral hydrophobic selectors. A comparison with chromatographic procedures

In this work we study the micellar extraction of two amino acids, namely tryptophan and tyrosine, using N-n-dodecyl-L-proline (1) and trans-N-n-dodecyl-4-hydroxy-L-proline (2) as hydrophobic chiral selectors with copper(II) ions. In the first part of our study the solubilities of the two selectors 1 and 2 and their ability to form micelles are examined. Quantum mechanical calculations are performed to access their Gibbs solvation energies in order to explain their different behaviours. Micellar extraction is then studied using both selectors solubilised in non-ionic micelles. The results obtained are discussed and comparisons made with the data reported in the literature for similar selectors deposited onto an octadecyl silylated stationary phase in chromatographic procedures or solubilised in a real biphasic system in solvent extraction experiments.