FTIR spectroscopy has also been applied to investigate the extraction
mechanism. Two different solute solutions were extracted (1. 0.2 mol/L
H3BO3 dissolved in saturated magnesium
chloride; 2. 0.2 mol/L H3BO3 dissolved
in deionized water), each of which had the same pH and
H3BO3 concentration. Both extraction
tests were carried out under the same operating conditions. The samples
of organic and blank organic phases were analyzed by IR respectively,
and the results were shown in Fig. 12. It is obvious that the IR spectra
of two loaded organic phases are similar, indicating that the extraction
complexes in the organic phase is independent of whether
MgCl2 is present in the solution. Compared with the
blank organic phase, the absorption bands of O-H shifted significantly
from 3377 cm-1 to 3444 cm-1, but it
did not disappear and the intensity had been slightly reduced,
indicating the presence of TMPD that did not participate in the
reaction. The new absorption peaks observed at 1416
cm-1, 1339 cm-1 and 661
cm–1 were identified to alcohol O-H, C-O and B-O
bonds of the boric acid ester, respectively. We therefore conclude that
the O-H groups of the alcohol are complexed with boric acid. The
evidence for the extraction complex is similar to the results obtained
previously by our group using
2-butyl-1-n-octanol[28]. The results will be
helpful to understand the mechanism of the complexation reaction between
alcohol extractants and boron.