Gérard Cote

Co(II) removal by magnetic alginate beads containing Cyanex 272

In this study, a series of batch experiments is conducted to investigate the ability of magnetic alginate beads containing Cyanex 272 to remove Co(II) ions from aqueous solutions. Equilibrium sorption experiments show a Co(II) uptake capacity of 0.4 mmol g(-1). The data are successfully modelled with a Langmuir equation. A series of kinetics experiments is then carried out and a pseudo-second order equation is used to fit the experimental data. The effect of pH on the sorption of Co(II) ions is also investigated. Desorption experiments by elution of the loaded beads with nitric acid at pH 1 show that the magnetic alginate beads could be reused without significant losses of their initial properties even after 3 adsorption-desorption cycles.

An Additional Insight into the Correlation between the Distribution Ratios and the Aqueous Acidity of the TODGA System

Abstract Extraction of Eu(III) and Am(III) from HNO3 into the organic solvents using N,N,N′,N′‐tetraoctyl‐diglycolamide (TODGA) was investigated in order to study the detailed extraction reaction. The chemical species: 1:2 for metal:TODGA complex is present in polar diluents. On the other hand, the metal complexes need three or more TODGA molecules to remain stable in non‐polar diluents. The HNO3 concentration dependence on the distribution ratio suggests that HNO3 participates in the metal extraction. Infrared spectra indicate that the carbonyl oxygen coordinates with Eu(III), and luminescence lifetimes suggest that there are no water molecules in the inner coordination sphere of the extracted Eu‐complex.

MODELLING OF EXTRACTION EQUILIBRIUM FOR COPPER( II) EXTRACTION BY PYRIDINECARBOXYLIC ACID ESTERS FROM CONCENTRATED CHLORIDE SOLUTIONS AT CONSTANT WATER ACTIVITY AND CONSTANT TOTAL CONCENTRATION OF IONIC OR MOLECULAR SPECIES DISSOLVED IN THE AQUEOUS SOLUTION

Abstract The extraction of copper(D) from concentrated chloride ion solutions by various pyridinecarboxylic acid esters is investigated. It is shown that the efficiency of the extraction is strongly dependent on the water activity (aw) and total concentration (σ) of ionic or molecular species dissolved in the aqueous phase. For decyl nicotinate, decyl isonicotinate, decyl picolinate and ACORGA CLX-50 (all denoted EXT) in toluene, the distribution of copper(II) can be satisfactorily represented by the formation of CuCl2(EXT)2 in the organic phase on the condition of taking into account the existence of CuClx (2-X) complexes (x = 1 to 4) in the aqueous phase. The apparent extraction constant KeX and stability constants |βi of the variousCuOx (2-X) complexes are estimated for two aqueous media corresponding to aw andσ= 0.835 and a = 8.0 mol.L-1, and aw = 0.617 and σ = 12.0 mol.L-1, respectively. On the other hand, in the case of ACORGA CLX-50 in kerosene, more complex phenomena influencing the activity coeff...

Recovery of Uranium from Wet Phosphoric Acid by Solvent Extraction Processes

Between 1951 and 1991, we developed about 17 processes to recover uranium from wet phosphoric acid (WPA), but the viability of these processes was subject to the variation of the uranium price market. Nowadays, uranium from WPA appears to be attractive due to the increase of the global uranium demand resulting from the emergence of developing countries. Moreover, the increasing demand provides impetus for a new look at the applicable technology with a view to improvements as well as altogether new approaches. This paper gives an overview on extraction processes developed in the past to recover uranium from wet phosphoric acid (WPA) as well as the physicochemistry involved in these processes. Recent advances concerning the development of new extraction systems are also reported and discussed.

Extraction of Lanthanides(III) and Am(III) by Mixtures of Malonamide and Dialkylphosphoric Acid

Abstract N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide, DMDOHEMA, and di‐n‐hexylphosphoric acid, HDHP, are the extractants of reference for the French DIAMEX–SANEX process for the separation of trivalent actinide ions from the lanthanide ions. In this work, the extraction of Eu3+ and Am3+ by the two extractants, alone or in mixtures, has been investigated under a variety of experimental conditions. The two cations are extracted by HDHP as the M(DHP · HDHP)3 complexes with an Eu/Am separation factor of ∼10. With DMDOHEMA, Eu3+ and Am3+ are extracted as the M(NO3)3(DMDOHEMA)2 disolvate species with an Am/Eu separation factor of ∼2. The metal distribution ratios measured with a mixture of the two reagents indicated that almost all lanthanides are extracted equally well. The extraction of Eu3+ and Am3+ by HDHP‐DMDOHEMA mixtures exhibits a change of extraction mechanism and a reversal of selectivity taking place at ∼1 M HNO3 in the aqueous phase. Below this aqueous acidity, HDHP dominates the metal extraction by the mixture, whereas DMDOHEMA is the predominant extractant at higher aqueous acidities. Some measurements indicated apparent modest antagonism between the two extractants in the extraction of Eu3+ and synergism in the extraction of Am3+. These data were interpreted as resulting from the formation in the organic phase of mixed HDHP‐DMDOHEMA species containing two HDHP and five DMDOHEMA molecules.

HYDROMETALLURGY OF STRATEGIC METALS

ABSTRACT This paper gives a short overview of the importance of solvent extraction in the production and recycling of strategic metals. Both the present situation and possible developments are considered. The use of solvent extraction in the processing of powdered metal-containing materials with tailor-made characteristics is also discussed as it is attracting increasing attention.

Aggregation in Solvent Extraction Systems Containing a Malonamide, a Dialkylphosphoric Acid and their Mixtures

Abstract Aggregation phenomena in n-alkane solutions of di-n-hexylphosphoric acid (HDHP), N,N′-dimethyl-N,N′-dioctylhexylethoxymalonamide (DMDOHEMA), and their mixtures, were investigated by electrospray ionization–mass spectrometry (ESI-MS), vapor pressure osmometry (VPO), and small-angle X-ray and neutron scattering (SAXS and SANS). The objective of the study was to probe the formation of mixed HDHP-DMDOHEMA species before and after extraction of trivalent lanthanide and actinide (M3+) nitrates. The most important species formed by HDHP upon metal extraction has the composition M(DHP)3(HDHP)3(H2O). These species exist as spherical aggregates of the reverse micelle type with a polar core diameter of ∼ 7 Å and total diameter of ∼ 11 to ∼ 15 Å. The aggregation of DMDOHEMA is a progressive phenomenon, with an average aggregation number of ∼ 2 in the 0.2 to 0.6 M range and larger aggregates forming at higher concentrations. The metal loaded DMDOHEMA aggregates can be considered as interacting spheres with a polar core diameter between ∼ 11 and ∼ 16 Å, depending on composition, a total diameter of up to ∼ 25 Å, and a weight-average aggregation number of ∼ 9. The results obtained in this work provide strong evidence for the formation of mixed aggregates when mixtures of HDHP and DMDOHEMA are used for the extraction of trivalent Ln and An cations. These mixed reverse micelles have a diameter between 19 and 24 Å with a polar core diameter of 10 and to 14 Å. The most recurrent micellar composition is 2 HDHP and either 4 or 5 DMDOHEMA molecules.

Cloud point extraction : An alternative to traditional liquid-liquid extraction for lanthanides(III) separation

Cloud point extraction (CPE) was used to extract and separate lanthanum(III) and gadolinium(III) nitrate from an aqueous solution. The methodology used is based on the formation of lanthanide(III)-8-hydroxyquinoline (8-HQ) complexes soluble in a micellar phase of non-ionic surfactant. The lanthanide(III) complexes are then extracted into the surfactant-rich phase at a temperature above the cloud point temperature (CPT). The structure of the non-ionic surfactant, and the chelating agent-metal molar ratio are identified as factors determining the extraction efficiency and selectivity. In an aqueous solution containing equimolar concentrations of La(III) and Gd(III), extraction efficiency for Gd(III) can reach 96% with a Gd(III)/La(III) selectivity higher than 30 using Triton X-114. Under those conditions, a Gd(III) decontamination factor of 50 is obtained.

Extraction of chromium (III) from spent tanning baths

Extraction of chromium(III) from a model spent tanning bath of the leather industry has been investigated using ammoniated and non-ammoniated di(2-ethylhexyl)phosphoric acid (D2EHPA) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex® 272). Chromium extraction of 95% by 15% (v/v) D2EHPA, 10% (v/v) isodecanol in kerosene and 86.1% by 15% (v/v) Cyanex® 272, 10% (v/v) p-nonylphenol in kerosene was obtained at equilibrium pH values of 4.0 and 5.0, respectively. The separation of small amounts of iron (III) and aluminium (III) present in the solution along with the Cr(III), was also examined and it was found that Cyanex® 272 was a better reagent than D2EHPA. The slow kinetics of extraction and stripping observed in the case of AI(III) was advantageous for its separation from Fe(III) at low pH values. Difficulties faced in the stripping of loaded metals were also studied because only about 80% chromium recovery by 8 M HCl was obtained from both solvents. The incomplete stripping of the metal may be a result of the formation of a stable species in the organic phase and needs further investigation. The Cr(III) can be recovered as chloride from the strip liquor and recycled for retanning purposes.

Modelling of extraction equilibrium for zinc(II) extraction by a bibenzimidazole type reagent (ACORGA ZNX 50) from chloride solutions

The extraction of zinc(II) by ACORGA ZNX 50 (a bibenzimidazole-based extractant) from chloride ion solutions was investigated at constant water activity (aw) and constant total concentration (σ) of aqueous species. It is shown that zinc(II) is extracted as a binuclear complex according to the following equation: 2Zn+ 4Cl- + 2L⇔(ZnCl2L)2 with Kex = [(ZnCl2L)2][Zn2+]−2[Cl−]−4[L]−2. It is also shown that the chloride ions favour the extraction of zinc at low concentrations (i.e., [CI−] < 1 M), but have a depressing influence at higher concentrations, as a result of the formation of ZnCl3− and ZnCl4− species in the aqueous phase. At constant aw and σ, the plot of zinc concentration in the organic phase versus chloride ion concentration exhibits a maximum at about 1 M Cl−. The distribution of zinc(II) can be satisfactorily simulated with the following series of constant values: (l) log β1 =0.l, log β2 = 0.5, log β3 = 0.7, log β4 = −0.2 and log Kex = 4.05 ± 0.10, at aw = 0.83 and σ = 8 M; (2) log β1 = 0.4, log β2 = 1.1, log β3 = 1.4, log β4 = 1.25 and log Kex = 7.35 ± 0.10, at aw = 0.62 and σ = 12 M; with β1 = [ZnCIi−1][Zn2+]−1[Cl−]−i. The water activity of the aqueous phase has a strong influence on the value of the extraction constant (Kex).