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.