4. Conclusions
The extraction of boron using TMPD dissolved in carbon tetrachloride was
systematically investigated. The effects of extraction parameters were
obtained by varying the pH of feed brine, the concentrations of TMPD and
H3BO3,and the phase ratio (O/A). The
suitable pH range of the TMPD/CCl4 extraction system is
≤7. Logarithm linear regression revealed
that 1or 2 equivalent of TMPD were
complexed with a single H3BO3 molecule,
the formation of which was connected with the concentration ratio of
TMPD/H3BO3. The addition of magnesium
chloride showed two opposite effects on the boron extraction, and the
lower the pH value, the more promotion effect on boron extraction
obviously. The values of ΔH and ΔG obtained from the
temperature dependence data of extraction efficiency revealed that the
extraction process is endothermic and spontaneous. Results from Raman
spectra indicated that B(OH)3 was gradually converted to
[B(OH)4]- as the pH of the
solution increased, and B(OH)3 was more easily complexed
with TMPD, following which the FTIR spectra was used to analyze the
organic phase loaded with boron, the results of which indicated that the
O-H groups of the extractant molecule were complexed with boron. On the
basis of optimizing the extraction and stripping process, the
multi-stage extraction experiments were carried out in the separation
funnels, and the experimental results showed that the overall extraction
efficiency of boric acid was 97.12%, and the stripping efficiency was
88.98%. This study provides a route to extract boron from the salt
lakes brine without acidification. However, the feasibility of this
extraction process still requires further investigations.