Fig. 12. IR spectra of the organic phases. The organic phase after extraction of (1) H3BO3 dissolved in saturated magnesium chloride, (2) H3BO3 dissolved in deionized water; (3) The organic phase before extraction.

3.3 Three-stage continuous countercurrent extraction

In order to completely extract H3BO3from brine, we performed an experiment using the three-stage continuous countercurrent extraction (O/A=1) determined by the McCabe-Thiele method (as shown in Fig. 13). SL brine presented in Table 1 was used as aqueous phase. 0.4 mol/L TMPD dissolved in CCl4 was used as organic phase. The experiment results are listed in Table 4. Finally, the raffinate of 0.0253 g/L H3BO3 and the organic containing 12.340 g/L H3BO3were obtained, which corresponds to an extraction efficiency of H3BO3 of 99.79%. The results show that the extraction efficiency of H3BO3 and distribution ratio are significantly improved in three-stages countercurrent extraction, and boric acid was almost extracted completely.
Table 4. Comparison of single-stage and three-stage experiment results.