Fig. 1. Flow chart of three-stage continuous countercurrent extraction.
The separatory funnel with numbers represents a single extraction.
A(1-3) and O(1-3) represent the aqueous and organic phases after
extraction to reach equilibrium, respectively.
2.4 Analysis
Metal ions concentration of aqueous phase was determined by inductively
coupled plasma-atomic emission spectroscopy (ICP-AES) (ICAP6500 DUO;
America Thermo Scientific). The concentrations of boric acid in aqueous
phase were determined by titration[27], but the
trace amounts of boric acid were
measured
by ICP-AES. The boron in the organic phase was stripped into the aqueous
for analysis, so the accuracy of the analysis can be verified by the
mass balance of the boron in the two phases. The pH of all liquid
samples was measured by a pH meter (Seven excellence, Mettler Toledo).
After extraction, the organic phases with and without boron complexes
were measured by FTIR spectra (Thermo Nicolet Corporation 670
Spectrometer). Raman spectrometer (DXR; American Thermo Fisher
Scientific Co., Ltd.) has been used to characterize the presence of
boron in the aqueous phase.
In this study, the extraction efficiency (E ) and distribution
ratio (D ) were calculated by the
formulas[28]:
E =\(\frac{\text{\ \ \ \ }V_{\text{org\ }}\ {*\ \ \left[B\right]}_{\text{org\ \ \ }}}{\ V_{\text{aq\ }}\ {*\ \ \left[B\right]}_{\text{aq\ \ \ }}+\ \ V_{\text{org\ }}\ {*\ \ \left[B\right]}_{\text{org\ \ \ }}}\)*100%
Eq. (1)
D =\(\frac{\text{\ \ \ }{\text{\ \ }\left[B\right]}_{\text{org\ \ \ \ \ }}}{{\text{\ \ \ \ \ }\left[B\right]}_{\text{aq\ \ \ \ \ }}}\)Eq. (2)
where [B]org and
[B]aq are the equilibrium concentrations of
boron in the organic and aqueous phases, respectively.