• The existing forms of impurity iron in electrolytic magnesium were analyzed. • Force-balance analysis indicated that Fe-rich inclusions can be entrained by magnesium vapor during vacuum sublimation. • The feasibility of employing a Ti-Si composite filter to intercepting micron-sized Fe-rich particles was demonstrated. • A purification strategy integrating vacuum sublimation with filter interception was proposed. • Purified magnesium with 99.995% purity was obtained without secondary contamination. Electrolytic primary magnesium generally contains elevated Fe impurities, which severely degrade corrosion resistance, thus limiting downstream use. Although vacuum sublimation, in principle, should separate Fe from magnesium because Fe is far less volatile, the purified condensate frequently remains Fe-rich. Here we identify that Fe resides mainly in micrometer-scale inclusions (elemental Fe and Fe-bearing intermetallic particles). Through analysis of the drag force exerted by magnesium vapor on these inclusions, we determine that they can be entrained in the vapor stream, thus bypassing separation based solely on volatility difference. To intercept these particles, we implement an in-line filtration positioned in an appropriate thermal zone along the vapor route, and select Ti mesh packed with Si particles as the interception medium based on thermal stability, affinity for impurity species, and cost. In controlled comparisons using industrial electrolytic magnesium (258 ppm Fe), sublimation alone lowers Fe to 76 ppm, Ti-mesh filtration lowers it to 28 ppm, and Ti-Si integrated trapping to 4 ppm, meeting the Mg9999 specification without detectable Ti or Si contamination. These results establish particulate entrainment as a principal barrier to deep purification by sublimation and provide a practical framework for upgrading electrolytic magnesium via targeted particle interception and rational trap design.
Gao et al. (Fri,) studied this question.