The dehydration of MgCl2·6H2O in MgCl2·6H2O–KCl–NH4Cl system

• Anhydrous KMgCl3 is more stable than anhydrous MgCl2 at high temperature.
• NH4Cl·MgCl2·nH2O and KMgCl3 can facilitate the dehydration process.
• The magnesia content in anhydrous magnesium chloride can reach 0.02 wt.%.
• NH4Cl·MgCl2·nH2O is formed below 300 °C, KMgCl3 is formed over 400.

The dehydration of MgCl2·6H2O in MgCl2·6H2O–NH4Cl–KCl system was investigated. The dehydration process was characterized by X-ray diffraction and chemical analysis. The dehydration effects of MgCl2·6H2O in different systems were compared. The dehydration mechanism of MgCl2·6H2O in MgCl2·6H2O–NH4Cl–KCl system was proposed and discussed. The formation of NH4Cl·MgCl2·nH2O (6 > n ≥ 0) below 300 °C can effectively suppress hydrolysis. The anhydrous KMgCl3 formed above 400 °C is more stable than anhydrous MgCl2 at elevated temperature, which can effectively protect the dehydration product from hydrolyzing at high temperature. The content of MgO in anhydrous MgCl2 was 0.02 wt.% when dehydrating MgCl2·6H2O in MgCl2·6H2O–KCl–NH4Cl system with the molar ratio of MgCl2·6H2O:KCl:NH4Cl was 1:2.87:1.