Increasing scrap recyclingRecycling inevitably enriches low-melting-point residual elementsResidual element like arsenicArsenic in steelSteel, adversely affecting the quality and propertiesProperties of steelSteel products. Rare earthRare earth elements (REEs) have been proved to mitigate arsenicArsenic segregation by forming high-melting-point compounds. Our recent works revealed that lanthanum can remove arsenicArsenic from molten steelSteel by forming La–S–As ternary compounds that float up the surface of the molten steelSteel or adhere to the crucible wall. Combining mismatch calculations and experiments, this study elucidated sulfurSulfur’s role in RE dearsenication and demonstrates how sulfurSulfur and lanthanum contents influenced arsenic removalRemoval in bearing steelSteel, and an optimal sulfur contentSulfur content of approximately 0.0100 wt% for maximum dearsenication rate at an initial arsenicArsenic level of 0.0150 wt% was obtained. Both insufficient and excessive sulfurSulfur reduce the removalRemoval efficiency of arsenicArsenic, while higher lanthanum content enhances it. These findings offer a control strategy for solving the problem of residual elementsResidual element enrichment in steelSteel.