Preparation and characteristic research of anhydrous magnesium chloride with dehydrated ammonium carnallite

Abstract

Taking the saline lake bischofite and NH₄Cl that was removed with the ammonia method and continuously followed by filtration as raw materials with a molar ratio of 1 : 1 of MgCl₂ to NH₄Cl, ammonium carnallite was synthesized. And then the ammonium carnallite was dehydrated to some extent at 160 °C for 4 h. Ammonium carnallite reacted with ammonia at 240 °C for 150 min and the ammonation ammonium carnallite was produced. Finally, the ammonation ammonium carnallite was calcined at 750 °C into anhydrous magnesium chloride containing only 0.1% (mass fraction) of MgO. On the other hand, dehydrated ammonium carnallite was mixed with the solid ammonium chloride at mass ratio 1 : 4 at high temperature and with the differential pressure of NH₃ above 30.5 kPa. The dehydrated ammonium carnallite of mixture was dehydrated at 410 °C, and then calcined at 700 °C into anhydrous magnesium chloride with only 0.087% (mass fraction) of MgO. X-ray diffraction and electron microscopy analysis results prove that anhydrous magnesium chloride obtained by both methods hasn’t mixed phases, the particle is large and even has good dispersion, which is suitable for preparation of metal magnesium in the electrolysis.