Preparation of Mg(OH)2 with caustic calcined magnesia through ammonium acetate circulation

• Caustic calcined magnesia (purity: 85 wt.%) is used to prepare highly pure Mg(OH)2 via ammonium-circulation method.
• Ammonium acetate (NH4Ac) is studied as a circulation medium.
• As a circulation medium, NH4Ac is much more efficient than NH4Cl, NH4NO3 or (NH4)2SO4.
• Purity of the prepared Mg(OH)2 is > 99% by using NH4Ac as the circulation medium.
• Rose petal-like Mg(OH)2 precipitate can be obtained.

Caustic calcined magnesia (main component is MgO) can be used to produce Mg(OH)2 by ammonium-circulation method (reaction steps: (1) MgO + 2NH4+ →Δ Mg2 + + 2NH3↑ + H2O and (2) Mg2 + + 2NH3↑ + 2H2O → Mg(OH)2↓ + 2NH4+; Overall: MgO + H2O → Mg(OH)2↓). NH4Cl, NH4NO3 and (NH4)2SO4 have exhibited the ability to be used as a circulation medium. In this work, ammonium acetate (NH4Ac) was investigated as a circulation medium. The purity of the used caustic calcined magnesia (i.e., MgO content) is 85 wt.%. The results show that NH4Ac is a much more efficient circulation medium than NH4Cl, NH4NO3 or (NH4)2SO4 is. Step (1) in the ammonium-circulation method can be significantly accelerated if NH4Ac is used as the circulation medium. The reason for the high efficiency of NH4Ac was also analyzed. By using NH4Ac as the circulation medium, rose petal-like Mg(OH)2 precipitate can be prepared in the presence of polyethylene glycol. The purity of the prepared Mg(OH)2 is more than 99 wt.%.