Christian Tondre

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.

Copper(II) complexation kinetics with hydroxyoximes in CTAB micelles. Effect of extractant hydrophobicity and additives

Micellar solutions can be considered as pseudo-biphasic systems in order to investigate the kinetics and mechanisms of metal ion complexation/extraction by hydrophobic chelating extractants. The kinetics of complexation of copper with a series of 2-hydroxy-5-alkylbenzophenone oximes of different hydrophobicities (the alkyl chains were methyl, tert-butyl and tert-octyl) in cationic micelles have been studied. The absorbance change recorded for the absorption band of the complexes followed first-order kinetics in only a few cases and only when the pH was buffered. In most cases the kinetic curves were best fitted with a biexponential function, with a slow absorbance change following faster complex formation. The influence of different parameters has been considered, i.e. surfactant concentration, copper concentration, pH, effect of added α-acyloin oxime. The results indicate a very strong partitioning of the three 2-hydroxy-5-alkylbenzophenone oximes in favour of the micellar pseudo-phase, and the apparent rate constants for complex formation decrease in the order methyl > tert-butyl > tert-octyl. The comparison with salicylaldoxime suggests that the mechanism is interfacial, whereas a bulk aqueous mechanism can take into account the data relative to salicylaldoxime itself. Possible origins of the slow relaxation process have been discussed. The trends observed in the change of the reaction rate with different parameters are compared with the behaviour previously reported for the rate of extraction in biphasic toluene–water systems using the ascending-drop method.

Metal extraction in micellar media: a comparison of copper complexation rates and ultrafiltration yields of two isomeric (E)-1-(2′-hydroxy-5′-alkylphenyl) 1-alkanone oximes

Copper(II) complexing and extracting properties in micellar media of two isomeric hydroxyoximes differing in the location of their hydrophobic alkyl chain [(E)-1-(2′-hydroxy-5′-nonylphenyl)-1-ethanone oxime (1) and (E)-1-(2′-hydroxy-5′-methylphenyl)-1-decanone oxime (2)] are compared. Stopped-flow kinetic measurements were conducted in cetyltrimethylammonium bromide (CTAB) and n-dodecyl hexa(ethylene glycol) ether (C12EO6) micelles and in methanol. The rates of complexation were very similar in methanol, while complexation in micellar solutions at pH 5 was faster with 2 than with 1. The pH dependence of the observed rate constants was consistent with a Hague–Eigen type mechanism.The practical removal of copper from dilute aqueous solutions was investigated using micellar extraction coupled with ultrafiltration. Close to 100% removal was achieved with both surfactant systems at pH 6.2, with a ligand : metal ration of 5. Ligand 2 appeared to be slightly more efficient than ligand 1. The effect of pH on extraction yield was studied in more detail with 1. The results of both the micellar extraction and kinetic studies have been discussed in relation to previous experiments involving classical extraction using water/xylene biphasic systems.

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.

An attempt to theoretically predict third-phase formation in the dimethyldibutyltetradecylmalonamide (DMDBTDMA)/dodecane/water/nitric acid extraction system

ABSTRACT The formation of a third phase in solvent extraction (due to splitting of the organic phase into two layers) often occurs when the aqueous phase is highly concentrated in acids. This has been reported with the extraction system dimethyldibutyltetradecylmalonamide (DMDBTDMA)/n-dodecane/water/nitric acid, both in the presence and absence of metal ions. Whereas many experimental efforts have been made to investigate the effects of different parameters on third-phase formation, very few attempts have been made to predict this phenomenon on theoretical grounds. Because the part played by aggregation of the extractant molecules is recognized, we propose a new predictive approach based on the use of the Flory-Huggins theory of polymer solutions, which had been successfully applied for the prediction of phase separation phenomena in nonionic surfactant solutions. We show that this model can provide an excellent prediction of the demixing curve (in the absence of metal ions) when establishing the relation...

Copper(II) complexation by micelle-solubilized long-chain complexing agents: Unusually slow reaction rates

Abstract We consider in this work the complexation of copper(II) by two different complexing agents [7-4(ethyl-l-methyloctyl)-8-hydroxyquinoline (C 11 ,-HQ) and 6-(hexadecylamino)methyl-2-hydroxymethylpyridine (C 16 NHMePyr)] in different kinds of micellar surfactant solutions (SDS, C 12 EO 6 , CTAB and mixed CTAB/butanol). Stopped-flow kinetic experiments at controlled pH have provided values of the apparent rate constants for complex formation, which are discussed with reference to literature data in homogeneous solutions. They show considerable rate decreases, especially in CTAB micellar systems.

On the kinetics of the micelle dissolution-formation equilibrium in solutions of cationic detergents: A comparison between temperature-jump and stopped-flow data

The kinetics of the micelle formation-dissolution reaction of dodecyl and tetradecylpyridinium bromides (C12PBr and C14PBr) and of dodecyltrimethylammonium chloride (C12TACl) has been investigated by means of temperature-jump and stopped-flow methods. The experiments have permitted the establishment of a correlation between the changes of the relaxation time τ2 upon changes of detergent concentration and upon changes of added salt or dye concentration. The stopped-flow method usually yields τ2 values which are larger than those measured by the temperature-jump method for a given system. However, the two sets of data become coincident, within experimental uncertainty, if the amplitude of the perturbation of the equilibrium achieved in both methods (mainly in stopped-flow) is extrapolated to very small values. A reinterpretation of previously reported stopped-flow measurements may be necessary in view of these results. Finally an unusual change in the apparent activation enthalpy of the micelle formation-dissolution equilibrium in C14PBr upon addition of KBr, together with nonlinear Arrhenius plots, has been observed. The results are discussed on the basis of the Aniansson and Wall theory for the kinetics of the stepwise micelle formation.

Transition Metal Complexes with 8-Hydroxyquinoline and Kelex 100 in Micellar Systems. Stoichiometry of the Complexes and Kinetics of Dissociation in Acid Media

Abstract Complexation of metal ions by micelle-solubilized extractants can be used for the development of new extraction processes. Metal extraction in micellar systems is in many respects analogous to solvent extraction if one considers the use of ultrafiltration as a means to separate the micellar pseudophase from the continuous aqueous phase. The present paper is intended to further characterize the nature of the complexes obtained in micellar systems (especially their stoichiometry and their stability as a function of pH) and to compare the results with those previously obtained in classical biphasic systems. The extractant molecules considered in this work were 8-hydroxyquinoline (HQ) and its alkylated analogue (C11-HQ) derived from Kelex 100. Their complexes with Ni2+, Co2+, and Cu2+ have been investigated in micellar solutions made of cetyltrimethylammonium bromide (CTAB), 1-butanol, and water. The stoichiometry of the complexes was determined using Jobs continuous variation method, and their kine...

Conductometric study of the interaction of 1:1 electrolytes with nonionic surfactants having short polyoxyethylated chains: Methanolic solutions of H- and F-alkylated surfactants and oil/water microemulsions

Electric conductivity measurements have been used to demonstrate the complexing ability of nonionic surfactants having short polyoxyethylated chains (nEO = 4 to 8) in methanolic solutions. The binding constants Kb have been found to be much larger for K+ than for Na+ but only weakly dependent on the nature of the associated anion (Cl−, I−, SCN−). The dependence of Kb on the length of the polyoxyethylated chain of the surfactant molecule has also been examined, showing a much more significant increase between nEO = 4 to 6 than between 6 to 8. F-alkylated surfactants show the same trends as H-alkylated surfactants but the binding constants are systematically lower. A quantitative evaluation has been performed leading to the following approximate relations: log KbH ⋍ log KbF + 0.56 (±0.12) for KI and log KbH ⋍ log KbF + 0.36 (±0.08) for NaCl. Finally, binding of K+ to o/w microemulsions including C12(EO)4 or C12(EO)6 has been shown to be very unlikely from the comparison of the conductivity data with those obtained for PEO chains.