Assessment of zinc migration behavior and toxicity characteristics in redox smelting of zinc leaching residue

• • Zinc recovery ratio of 99.13% and residual Zn content of 0.22 wt.% in slag were achieved under optimized redox smelting conditions, compared to the industrial baseline of 1.0–3.0 wt.%, directly reducing the hazardous waste classification and long-term environmental liability of the residue. • • The formation of a ZnS–FeS eutectic, promoted by CaSO4 in the leaching residue, was identified as the primary bottleneck for zinc recovery; this phase exhibits lower thermodynamic stability than (Fe,Zn)2SiO4, ZnFe2O4, and (ZnO)slag, necessitating temperatures above 1573 K to oxidize it to ZnO for subsequent reduction. • • Elevated temperatures (>1573 K) facilitate the oxidation of the ZnS–FeS eutectic by O2/(O)slag to ZnO(s), which then dissolves into the slag as (ZnO)slag and is finally reduced to Zn(g) by CO; this mechanism enables effective zinc volatilization and recovery. • • A novel treatment strategy combining desulfurization pretreatment with redox smelting is proposed, which lowers the required smelting temperature and improves zinc recovery efficiency, providing a more economical and environmentally sustainable route for treating zinc leaching residues compared to conventional methods.