In order to determine strategies for removing arsenic from rare earth arsenic-containing steels, the evolution of inclusions in the whole steelmaking process with alumina crucibles was investigated. It has been proven that adding lanthanum has a significant effect on both the existing state and content of arsenic in steel. The content of arsenic steeply decreased after adding 0.148% lanthanum by generating La–S–As inclusions. The addition of 0.054% lanthanum did not dramatically affect the content of arsenic. Both 0.148% and 0.054% additions of lanthanum modified the existing Si–Mn–Al–O inclusions, making them first change to La-containing inclusions, and then change back to Si–Mn–Al–O inclusions. During this process, the compositions of inclusions changed from (SiO₂–MnO)-rich to Al₂O₃-rich ones, owing to the reactions between lanthanum and alumina crucibles. The addition of 0.148% lanthanum resulted in a relatively severe reaction with the alumina crucible. This led to the decomposition of a part of the existing La–S–As inclusions and a slight increase in the arsenic content. Therefore, it is noted that choosing an appropriate holding time after adding rare earth elements to molten steel has a significant effect on the arsenic removal and saving the consumption of rare earth elements.

Trace element arsenic is detrimental to the quality and properties of steel products. We used lanthanum to modify the distribution of arsenic by the formation of arsenic rare earth inclusions and investigated all inclusions on the full profile of the ingots prepared in the laboratory. The results show that the addition of lanthanum has dramatically influenced the distribution of arsenic in the ingots by the formation of arsenic inclusions. The arsenic inclusions turn out to be mainly the cluster-shaped La-S-As, as well as its composite inclusions combined with LaS and La-As. La-S-As can be considered a solid solution of LaS and LaAs. They distribute mainly at the top surface of the ingots within 3 mm, at the side and bottom surfaces within 1.5 mm, leading to a dramatic decrease of arsenic concentration at the inner part of the ingots. This distribution characteristic of La-S-As can be used to manufacture steel ingots with very low arsenic concentration by peeling off these (La-S-As)-containing layers. On the contrary, the distribution of composite inclusions (La-S-As)-(La-As) and single-phase La-As, is uniform. Except for the reaction with arsenic, lanthanum can also react with phosphorous and antimony to modify the existing state of these trace elements.

Cleanliness control is an eternal theme to improve the properties of steel products. With the increasing recycling rates of scrap steel, the removal and stabilization of residual elements have become a vital issue for improving the performance of steel products. Thermodynamic and mismatch calculations plus laboratory experiments were carried out to study the heterogeneous nucleation phenomena of inclusions when lanthanum was employed to remove arsenic from molten steel and stabilize arsenic in solid steel. The effect of heterogeneous nucleation on the mechanism of arsenic removal was discussed. A series of heterogeneous nucleation phenomena of inclusions in the La-O-S-As system were discovered, and the heterogeneous nucleation among the inclusions turned out to be selective. As the vital product of arsenic removal, La-S-As is most likely to generate with LaS as heterogeneous nucleation cores, and its possible chemical formula turned out to be 3LaS⸱LaAs. Sulfur plays an essential role in removing arsenic from molten steel by adding lanthanum. It needs to control the initial sulfur content in an appropriate range, because the high initial content causes too much loss of rare earth, and the low initial content cannot produce LaS and La-S-As.