Beneficiation of ESP dust in sponge iron production: Efficient recovery of iron and carbon for waste reduction and resource cycling

Abstract

The BMM Ispat sponge iron plant in Hospet, Karnataka, produces 30 to 40 tons/day of electrostatic precipitator (ESP) dust containing 19.37% Fe, 25.32% SiO₂, 14.20% carbon and 0.338% sulphur, with 99.83% passing 150 microns. Magnetic separation yielded an iron concentrate with 50.55% Fe and 0.30% carbon (33.48% weight recovery), while flotation of the non-magnetic fraction produced a carbon concentrate with 52.5% carbon and 1.50% Fe, achieving an overall recovery of 59.46%. Partial substitution of hematite ore with 5% to 15% ESP concentrate in pellets improved green crushing strength (1.47–1.51 kg/pellet) but reduced cold compressive strength from 275 to 237 kg/pellet and increased porosity from 24.0% to 27.39% at 15% substitution, due to silica and alumina effects. Up to 10% substitution maintained acceptable strength. Process optimizations – adjusting basicity, increasing induration temperature and limiting ESP to ≤10% – are recommended for sustainable recycling and waste reduction.