Phase Equilibrium in Aqueous Systems Containing Magnesium Borate

The phase equilibria in the aqueous system containing magnesium borate at 0, 25, and 50°C was studied using isothermal dissolution equilibrium method, and the solubilities, and acidity were determined. Detailed investigation of aqueous hungchaoite solutions has been performed by Raman spectroscopy at 25°C. The results showed the phase transformation of hungchaoite has not appeared at 0°C, the B(OH)${}_4^{-}$ and B(OH)₃ are dominant species and the concentration of polyborate remain constant. It was found that hungchaoite will transform into inderite (Mg₂B₆O₁₁ · 15H₂O) in aqueous solution at 25 and 50°C and the value of mB₂O₃/mMgO has as clear ascendant trend after 240 and 10 h, respectively. The mole fractions of B(OH)₃ and B₃O₃(OH)${}_4^{-}$ are increasing, and the trend is opposite to B(OH)${}_4^{-}$ and B₄O₅(OH)${}_4^{2-}$. According to the experimental result, the relevant chemical reaction and mechanism were suggested in the dissolution and transformation processes.