Analysis of the behavior of NaF in the vacuum carbothermal reduction of magnesium oxide

Abstract

Vacuum carbothermal reduction method of magnesium has the potential to become a new green process to replace the pidgeon method. Adding catalyst to enhance the degree of reduction is highly significant for this method. In this work, the behavior of NaF during vacuum carbothermal reduction of MgO was thermodynamically analyzed, and the experimental results were characterized by XRD, XPS, SEM and EDS. Thermodynamic calculations showed that the reaction temperature for vacuum carbothermal reduction of MgO was above 1462 K(80 Pa), and NaF did not participate in reaction during the reduction process, which was mainly the effect of F−. Experimental analysis showed that the addition of NaF obviously improved the degree of reduction, the mass loss rate elevated with the increasing of NaF addition and holding time, when the addition amount was greater than 7%, the mass loss rate tended to level off, which is the result of the limited effect of F−. The purity of magnesium in the condensate reached more than 91.11% with a good crystallization and granular structure. NaF did not participate in the carbothermal reduction of magnesium in vacuum, where it plays a catalytic role in the process.