“Spray-Slag” – Processing of liquid blast furnace slag

The high viscosity of molten slags complicates the atomization and reduces the time available for spheroidization, which often leads to the formation of fiber material. To improve the generation of spherical particles, the use of hot gas in a new developed atomization plant is investigated. Initial trials and first optimization measures in the plant and the process parameters show a stabilization of the process and a reduction of the fiber content in the atomized product. Ongoing investigations demonstrate a high impact on the workability of cement pastes when using the spherical atomized particles as an additive.
In Europe, about 18 million tons of blast furnace slags were produced in 2020 as a by-product of iron production in blast furnaces. In this, approximately 90 % of the slag is used as granulated blast furnace slag for producing cement (e.g. production of CEM II or CEM III cements) (Merkel 2021). In this way, natural resources and emissions have been saved from using granulated blast furnace slag instead of clinker in the cement production. The morphology of slag particles in the cement have an important influence on the processability, quality and composition of a concrete. The conventional treatment process of the slag consists of wet granulation, drying and grinding. This results in irregular edge-shaped particles. However, powders consisting of spherical particles have a better flowability and therefore may reduce the amount of water necessary in the production of the concrete. Following the technological rule that the strength of a concrete is controlled via the water-cement-ratio of the binder, the possible water
reduction may reduce the cement demand. As the cement production is a high emission process, this approach may therefore contribute to climate protection measures.