Optimization of Falcon concentrator for iron recovery from blast furnace sludge using Box–Behnken design

Abstract Blast furnace sludge (BFS) is an iron and carbon rich by-product whose direct recycling to ironmaking routes is often constrained by its fine particle size and the presence of volatile/corrosive species. This study evaluates Falcon enhanced gravity separation as a physical pre-treatment for iron upgrading from fine-grained BFS and optimizes operating conditions using Response Surface Methodology (RSM) with a three-factor, three-level Box-Behnken design (solid ratio 10–30%, fluidization water pressure 0.5–1.5 psi, and G-force 50–250 G). Statistical modeling confirmed that fluidization water pressure and G-force dominate separation performance, producing a clear grade–recovery trade-off: increasing water pressure improves Fe grade but reduces recovery, whereas increasing G-force tends to increase recovery while diluting grade. The BFS feed contained 34.40% Fe, 18.44% C and 2.94% Zn, under multi response optimization, the validation test yielded a concentrate grading 51.42% Fe at 57.88% Fe recovery. A two-stage scavenging configuration increased overall recovery to 77.52% at 49.35% Fe in the final concentrate. The results demonstrate that an optimized, two-stage Falcon circuit can effectively upgrade BFS and reduce mass for downstream treatment, while noting that Zn remains concentrated in the Fe-rich stream and may require subsequent removal depending on the intended metallurgical route.