Recovery of zinc and iron from basic oxygen steelmaking filter cake: A pathway to cleaner and circular steelmaking

• Zn separation graphite cell enables selective Zn/Fe phase separation. • 97 % Zn and 99 % Pb removed at 1100 °C via thermal volatilization. • Controlled C input reduced Fe oxides, yielding residue containing 87 wt% Fe. This study explores a pyrometallurgical route for recovering zinc (Zn) and iron (Fe) from basic oxygen steelmaking (BOS) filter cake—an industrial by-product rich in Zn and Fe but difficult to recycle—using a newly designed graphite-based Zn separation cell. The effects of temperature and carbon content on Zn and Fe recovery were systematically examined. Zn recovery exceeded 96 % at temperatures above 1000 °C, driven by the preferential reduction–volatilization of Zn oxides at elevated temperatures. At 1100 °C, Fe recovery reached 87 % in the solid residue, enabled by the carbon-facilitated reduction of Fe oxides that promoted the aggregation of a metallic Fe-rich phase. Lead (Pb) removal was strongly temperature-dependent, exceeding 99 % at 1100 °C, as Pb oxides underwent efficient volatilization under thermal treatment. Increasing carbon content further enhanced Zn recovery, reflecting the strengthened reduction–volatilization pathway, while having minimal influence on Pb removal. In addition, potential slag–metal separation at high temperatures was observed, with the formation and stability of a metallic Fe-rich phase ensuring compatibility for direct reuse in steelmaking processes. These findings highlight not only the feasibility but also the underlying physicochemical principles of a thermal strategy for BOS filter cake recycling, thereby advancing sustainable resource recovery and utilization in the steel industry.