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The molecular organization of N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA), the current reference extractant for the DIAMEX (DIAMide EXtraction) process, is correlated with its water extraction properties from neutral media. The aggregation of DMDOHEMA in n-heptane was investigated by vapor pressure osmometry (VPO) and the aggregate speciation characterized by combined small-angle neutron and X-ray scattering (SANS and SAXS, respectively). Two approaches were taken to model the aggregation of the diamide and the water extraction as a function of the diamide concentration by taking into account a single aggregation equilibrium with an average aggregation number N equal to 4.28 ± 0.05; and a competition between two types of aggregates in the organic phase, namely, aggregates of the reverse micelle type with 4 diamides per aggregate, and an oligomeric structure composed of about 10 diamide molecules which appears at high extractant concentration (>1 mol/L). In both cases, the supramolecular speciation representing the monomers/aggregates distribution was determined, and for each supramolecular organization, a solubilization parameter was calculated using the Sergievskii-Dannus relationship. Thus, the correlation between the two types of micellization of the diamide and the extraction of water into the organic phase was demonstrated. The larger aggregates can extract about five times more water than monomers. [ABSTRACT FROM AUTHOR]

A thermodynamic model that allows one to determine the number and the stoichiometry of the complexes formed between nitric acid, neodymium nitrate (Nd(NO3 ) 3), and octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) diluted in nitrophenylhexyl ether (NPHE) also called 1-(hexyloxy)-2- nitrobenzene, is presented in this work. The Mikulin-Sergievskii-Dannus' model was used to model the extraction at 25°C of the HNO3-H2O-NPHE, HNO3-H2O-CMPO 0.2 mol kg-1-NPHE, Nd(NO3)3-H3O-CMPO 0.2 mol kg-1-NPHE and Nd(NO3)3-HNO3-H2O-CMPO 0.2 mol kg-1-NPHE systems. The stoichiometric mean activity coefficients of components in the binary aqueous phases were determined by interpolation from the experimental data published in the literature. For mixtures, they were calculated from experimental data using the Mikulin's equation, whereas the activity coefficients of the species in the organic phase were calculated from the Sergievskii-Dannus' equation. A satisfactory description of the distribution of neodymium nitrate, nitric acid, and water was then obtained over a wide range of neodymium and nitric acid concentrations in the aqueous phase by taking into account the formation of the following complexes: (HNO3)(NPHE), (HNO3)(H2O)(NPHE), (HNO3)(H2O(CMPO)2, (HNO3)(CMPO) (HNO3)2(CMPO), (HNO3)3(CMPO) (Nd(NO3)3(CMPO)3 (1 : 3), (Nd(NO3)3(CMPO)2 (1 : 2) (Nd(NO3)3(CMPO) (1 : 1), (Nd(NO3)3(CMPO)3 (1 : 1 : 3), (Nd(NO3)3(HNO3(CMPO)2 (1 : 1 : 2) and (Nd(NO3)3)(HNO3)(CMPO) (1 : 1 : 1). [ABSTRACT FROM AUTHOR]

A thermodynamic model that allows one to determine the number and the stoichiometry of the complexes formed between trivalent lanthanide(Ln) nitrates—Pr(NO3)3, Nd(NO3)3, Sm(NO3)3, Eu(NO3)3, Gd(NO3)3, and Yb(NO3)3—and octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide(CMPO) diluted in nitrophenylhexyl ether(NPHE) is presented in this work. The Mikulin–Sergievskii–Dannus'model was used to model the extraction at 25°C of the Ln(NO3)3–H2O–CMPO 0.2 mol kg−1–NPHE system with or without a salting-out agent. The stoichiometric mean activity coefficients of components in the aqueous phase were calculated from experimental data using the Mikulin's equation, whereas the activity coefficients of the species in the organic phase were calculated from the Sergievskii–Dannus'equation. A satisfactory description of the distribution of lanthanide nitrate and water was then obtained over a wide range of lanthanide concentration in the aqueous phase by taking into account the formation of the following complexes:[Ln(NO3)3](CMPO)3(1:3),[Ln(NO3)3](CMPO)2(1:2), and[Ln(NO3)3](CMPO)(1:1). [ABSTRACT FROM AUTHOR]