Sustainability study of carbothermic reduction of mill scale briquettes as alternative burden to induction furnace-based steel melting

This study focuses on the recycling of mill scale of AISI 4330 V grade using induction furnace melting. The prime objective of the work is to establish a viable pathway for efficient recovery of iron, nickel and molybdenum from briquettes made of mill scale using carbothermic reduction utilising Calcined Petroleum Coke (CPC) as a reducing agent. Briquettes were prepared by grinding mill scale into powder and mixing it with CPC and molasses as a binder. Chemical composition analysis, X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were conducted to assess the effectiveness of the recovery of metals from mill scale. Both stoichiometric calculations and TGA analysis signified that, briquettes with 10% to 12% carbon can give best reduction results. Subsequently, induction furnace experiments were conducted, varying the proportion of charge constituents for making melt pool. Results indicated that using mild steel (MS) plates for making melt pool improved recovery rates compared to using pig iron. A respective recovery of 99.36%, 75.52% and 97.01% was achieved for iron, nickel and molybdenum. A rise of 24.44%, 14.45% and 47.47% was observed in recovery of iron, nickel and molybdenum, respectively, in route using MS plate for making melt pool in comparison with route using PI for making melt pool. XRD study of slag produced in various routes was conducted to assess the presence of phases which indicates loss of elements into the slag. Substantial recovery of iron, nickel and molybdenum was observed in the final ingot contributing towards circular economy. Furthermore, energy requirements for the recycling process were calculated and it was observed that significant portion of energy (78.55%) was consumed in the reduction process.