Using blast furnace slags sustainably

Slags in hot demand

Liquid blast furnace slag is processed into ground granulated blast furnace slag and used in the cement industry, where it replaces clinker burned from limestone, thus saving a much-used primary raw material. This reduces the use of CO₂-emitting processes in the cement industry, resulting in a smaller CO₂ footprint: with blast furnace slag cement consisting of 60 percent blast furnace slag, CO₂ emissions are halved compared with classic Portland cement.

Frost- and weather-resistant steel slags (also: LD slags) are used, for example, in road construction or as high-grade chippings in asphalt wearing courses. In coastal protection, high-density LD slags are used to secure maritime structures. As fine-grained converter lime, they also play a role in the fertilizer industry: the slags supply crops with important nutrients such as silicon, magnesium and calcium. The diverse use of LD slags means that less natural stone is needed, thus also reducing energy-intensive mining processes.

Back into the cycle

Dusts, sludges and mill scale are further byproducts of steel production. In some cases they contain high amounts of iron and carbon. thyssenkrupp Steel recycles both back into production using the so-called Oxycup process. In this way waste is avoided – a contribution to the circular economy.

Byproducts from pickling, including iron oxide, iron(II) sulfate and iron(II) chloride, are used in wastewater treatment, the pigment industry and for high-tech applications in magnet production and solar energy. Here, too, recycling helps reduce industrial waste.

With CO₂ to a new product

Calcium carbonate (CaCO₃) is a fine white powder used in the paper industry as a pigment for coated papers. thyssenkrupp Steel is working on an innovative process to extract this high-purity material from steel slag and also investigating to what extent surplus CO₂ from the production process can be used for this – a further step on the way to the climate-neutral steel mill.

By keeping the byproducts of the steel industry in the value chain we are supporting the transformation of our company into a climate-neutral steelmaker and at the same time helping other industries reduce their own CO₂ footprint.

Christian Renner, Head of Mill Byproducts and Waste Materials