Extraction of light group lanthanide nitrates by a binary extractant based on di-(2-ethylhexyl)phosphoric acid and trioctylamine

The process of extracting the light group lanthanide nitrates from neutral aqueous solu-tions with a binary extractant based on di-(2-ethylhexyl)phosphoric acid (HA), tri-n-octylamine (NR3) and solvating additive of tri-n-octylamine nitrate in a non-polar organic diluent was investi-gated in this study. Using neodymium nitrate as an example, it was shown that this extractant (NR3HA+NR3HNO3) extracts Ln(NO3)3 according to the laws of binary extraction. The cation and anion of the inorganic salt pass into the organic phase in a stoichiometric ratio. The extraction isotherms of lanthanide nitrates are S shape, and only slight variation of pH is observed during the extraction. Based on the study of the absorption spectra of Nd complexes in the organic phase, it was found that at low concentration the Nd form a complex (NdA3)center dot NR3HNO3, and at a high concentration of Nd (when the extraction is saturated), a compound of the composition (NdA2NO3)center dot NR3HNO3 is formed. The introduction of salting-out agents in the aqueous phase or the organic phase makes it possible to vary the distribution coefficients (DNd). With an increase in the concentration of sodium nitrate in the aqueous phase, DNd increases, and with an increase in the concentration of NR3HNO3, it correspondingly decreases. The introduction of the salting-out and solvating agent NR3HNO3 into the organic phase eliminates the formation of precipitation in the organic phase during the extraction of lanthanide nitrates. Quantitatively, the Nd extraction process in a wide range of Nd(NO3)3 concentrations and extractant compositions can be described on the basis of two coupled binary extraction equations and the corresponding concentration con-stants. It has been established that the proposed extractant provides high separation factors for neodymium and other light group lanthanides.