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

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℃ for 4 h. Ammonium carnallite reacted with ammonia at 240℃ for 150 min and the ammonation ammonium carnallite was produced. Finally, the ammonation ammonium carnallite was calcined at 750℃ 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 30.5kPa. The dehydrated ammonium carnallite of mixture was dehydrated at 410℃, and then calcined at 700℃ 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.

A novel pathway for the preparation of Mg metal from magnesia

High-purity anhydrous magnesium chloride was prepared from magnesia and ammonium chloride.The chlorination process was analyzed and then the critical stages affecting the purity of anhydrous magnesium chloride were pinpointed.The effect of sample dimension on the above critical stages was investigated respectively.The purity guarantee mechanism of anhydrous magnesium chloride was proposed.After that,magnesium metal was obtained via electrolyzing the anhydrous magnesium chloride-containing molten salt.The new process for the continuous production of magnesium metal from magnesia was proposed and discussed.The incomplete chlorination reaction and the hydrolysis of anhydrous magnesium chloride are the two critical stages affecting the purity of the anhydrous magnesium chloride.The dimension of the sample can influence reaction process and reaction mechanism,and thus the problems of incomplete chlorination reaction and hydrolysis can be solved together.The magnesia content in anhydrous magnesium chloride was below 0.1 wt.%when the ratio of height to diameter of the sample was over 2.43.The content of impurities in the magnesium metal obtained met the specifications of the product Mg9980.The current efficiency was(94.7±1.8)%and the electricity consumption was(9107±97)kW h/t.