Modeling of the extraction of nitric acid and neodymium nitrate from aqueous solutions over a wide range of activities by CMPO

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 degrees C of the HNO3-H2O-NPHE, HNO3-H2O-CMPO 0.2 mol kg(-1)-NPHE, Nd(NO3)(3)-H2O-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 phase, 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: [GRAPHICS]