Application of enhanced gravity technique for separation of iron phase from LD slag

Abstract

The basic oxygen process of steel making produces steel slag at a rate of about 120 kg/t. The steel slag also known as LD slag contains metallic iron and other mineral phases. The metallic iron is recovered through magnetic separation while the non-metallic is rejected because of its poor physical and chemical properties. Qualitative mineralogical analysis and XRD studies indicated that major mineral phases are dicalcium silicate and calcium ferrite. While both these phases are useful for recycling in iron making process the presence of phosphorus is a deterrent for its use in the iron making process. The electron probe micro analysis revealed that phosphorus is mostly associated with dicalcium silicate phase in the form of calcium phosphate. The phosphorus was present in negligible amounts in iron bearing phases i.e. calcium ferrite and wustite. The liberation size of phosphate mineral was in the range of 30–50 microns. The physical separation of phosphorus was attempted by grinding the LD slag to different sizes and then subjecting to centrifugal jigging. The centrifugal jigging was carried out at 0.5 mm, 0.25 mm and 0.1 mm size. The products of centrifugal jigging were characterised and it was observed that maximum recovery with acceptable grade of product was obtained at 0.5 mm grind size. The product obtained at this size analyzed 0.79% P and 34% Fe.