Eq. (3)

Boric acid is mainly present in a condition with the pH value lower than 9.23, and in a higher pH environment, borate ion is the main form. It is well known that boric and borate ion can react with polyhydroxy compounds to form complexes^[29]. The possible reaction mechanisms were shown in Fig. 3.

Fig. 2. Effect of simulated brine pH values on boron extraction. [TMPD] = 0.4 mol/L; O/A = 1.