Selective extraction of perrhenate anion in nitric acid solution using 2,2′-(imino)bis(N,N′-dioctylacetamide) as an extractant

In order to examine extraction behavior of ReO4- from HNO3 aqueous solution to dodecane containing 2,2'-(imino)bis(N,N'-dioctylacetamide) (IDOA) as an extractant, we have measured distribution ratios (D) by changing [HNO3] under constant [IDOA] (5.00 x 10(-2) M, M = mol dm(-3)) in dodecane and also by changing [IDOA] in dodecane under constant [HNO3] 0.1, 1.0, and 2.0 M. It was found that the D values decrease with an increase in [HNO3] and increase with increasing [IDOA]. The decrease in D values with increasing [HNO3] is considered to be due to effect of the protonation of IDOA in aqueous phase and also competitive extraction of NO3- with ReO4- from aqueous to organic phase. A plot of logD values against log[IDOA] gave the linear relationship with slope of ca. 1.03 +/- 0.01 ([HNO3] = 0.1 M), 1.02 +/- 0.01 ([HNO3] = 1.0 M) and 0.94 +/- 0.01 ([HNO3] = 2.0 M). These results suggest that one IDOA molecule contributes to the extraction of ReO4-. Effects of diluents (dodecane, toluene, dichloromethane) on the extraction of ReO4- with IDOA showed that IDOA exhibits higher extraction efficiencies into dodecane than toluene and dichloromethane. Furthermore, the influences of HNO3, H2SO4 and HCI on the extraction of ReO4- into dodecane were examined by changing their concentrations from 0.1 to 2.0 Mat [IDOA] = (5.00 x 10(-2)M). The results showed that the highest D values of ReO4- were observed in the H2SO4 system. The effects of the concentrations of the various salts ((NH4)(2)SO4, NH4CI, and NH4NO3) on the extraction of ReO4- into dodecane were also examined under constant [IDOA] (3.00 x 10(-2) M) and [acid] (0.1 M). It was found that the D values of ReO4- decrease with an increase in the concentrations of salts in the aqueous phase. These results suggest that anionic species (SO42-, Cl-, NO3-) are extracted with ReO4- from aqueous to organic phase. This is confirmed by the extraction experiments of (NH4)(2)SO4, NH4CI, and NH4NO3 in the absence of ReO4- using IDOA into dodecane. Hence, it was proposed that the decrease of D values with an increase in acid concentrations is due to the competitive extraction of anionic species (SO42-, Cl-, NO3-). (C) 2012 Published by Elsevier B.V.