Tungsten separation behavior on preparation of high-purity cerium by combined vacuum gravity sedimentation–directional solidification

Abstract

In light of the difficult removal of harmful impurity tungsten (W) in Ce metal, in this paper a combined vacuum gravity sedimentation‒directional solidification method was innovatively designed and the W separation behavior was investigated. By reducing the electron beam power instantly and gradually at reduction rates of 1, 3 and 5 kW/min, it is found that W is enriched at the bottom of ingots as the melt solidifies. The enrichment effect is much better than that of single purification method and the enrichment degree increases as the beam reduction rate decreases, attributed to the k0(W) ＞ 1 and ρ(W) ＞ ρ(Ce). Overall, the minimum content of W impurity can decrease from 630 to 0.1 ppm at the top of the ingot, and the purity of Ce increases from 99.932 wt% to 99.995 wt% by this combined method. Additionally, this paper provides a new method for the removal of high density and low evaporation coefficient impurities in low vapor pressure rare earth metals.