Dr Raymond Longbottom has been involved in metallurgy research since 2001, investigating aspects as diverse as alternate ironmaking, blast furnace ironmaking, steelmaking, and refractory corrosion. Recently, his focus has been on the utilisation and recycling of steel plant by-product materials such as basic oxygen steelmaking (BOS) filter cake. A common theme throughout his research has been improving the sustainability of the iron and steel industry.
The aim of his current project is to help realise the value in by-products through improved utilisation and on-plant recycling. This project has the following overall objectives:
- Realise value from by-products with primary focus on sustainable recovery of iron and flux (CaO, MgO, etc) units.
- Base characterisation data on steel plant by-product materials.
- Safe handling and characterisation procedures for these materials.
- Minimise emissions, stockpile volumes and costs to the steel industry.
The primary focus so far has been the characterisation of BOS filter cake, and relating this to an investigation into the self-sintering behaviour of the BOS filter cake. When stored in stockpiles prior to recycling, the BOS filter cake has a tendency to self-sinter, which is preferred for recycling as it has better handling/transport properties, with higher strength and larger particle size, when compared to the original filter cake. The self-sintering process has been shown to be driven by low temperature oxidation of very fine particles of metallic iron and wüstite to hematite and zinc ferrite. The processes involved in self-sintering and the changes involved in the material were identified through a number of different approaches. These included characterisation by high-resolution SEM; XRF; assessment of reactivity by TGA and TGA-DSC; and thermodynamic modelling using FactSage and MTDATA. These approaches were found to give consistent results. The low temperature reactivity of fresh BOS filter cake is likely to be as a result of the very fine particles of metallic iron and wüstite. The oxidation at low temperatures was exothermic, providing the energy required to heat the stockpiles and promote self-sintering.
There have been two main areas of impact of the project so far. The findings concerning the reactivity of the BOS filter cake have assisted with choices for on-plant process conditions around the dewatering of the BOS dust slurry. The characterisation of the BOS filter cake has also been used to inform and identify two further Steel Research Hub projects on processing of the BOS filter cake.
Another stream within the project has helped with the understanding of the behaviour of the activated char in the sinter plant waste gas cleaning, through the development of an assessment technique identifying the likelihood for combustion of the char during use.