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 × 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 log D 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 HCl on the extraction of ReO4- into dodecane were examined by changing their concentrations from 0.1 to 2.0 M at [IDOA] = (5.00 × 10−2M). 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)2SO4, NH4Cl, and NH4NO3) on the extraction of ReO4- into dodecane were also examined under constant [IDOA] (3.00 × 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)2SO4, NH4Cl, 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-).

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Extraction behavior of ReO4- from HNO3 solution to dodecane using IDOA is examined. ► One IDOA molecule contributes to the extraction of ReO4-. ► Effects of diluents on the extraction of ReO4- containing IDOA were examined. ► Effects of various acids on the extraction of ReO4- containing IDOA were examined. ► Effects of various anions on extraction of ReO4- using IDOA were also examined.