Slags, i.e. compounds of metals and other elements (mostly oxygen), are formed during the production of pig iron and crude steel. For metal production, this material cannot be reused at first because it is usually not economical to recover the metals. Nevertheless, the slags are not waste, since a large part is used as a building material.
However, the planned new substitute building materials ordinance (Ersatzbaustoffverordnung), which is to regulate the use of mineral substitute building materials nationwide in the future, will probably change the assessment procedure for whether a material is approved as a building material. According to the current state of the art, a large proportion of the slag produced in Germany from an electric arc furnace would then be classified as non-marketable - and would have to be disposed of in landfills.
In order to counter this development at an early stage, experts from industry and research are developing a large-scale plant in the “KONDEOS” project, with which various conditioning agents are added to the hot, liquid slag directly during tapping. In this way, the typical metals still contained in the slag from steel production are reduced and recovered. Furthermore, the structure and composition of the remaining slag is modified in such a way that the environmental properties and mechanical strength are similar to or even exceed those of natural stone. This ensures the economic stability of steel production, which would otherwise be massively endangered by high landfill costs or production stoppage due to insufficient landfill space.
Georgsmarienhütte GmbH, Hermann Rauen GmbH &
Co, DK Recycling und Roheisen GmbH & Co, the University of Duisburg-Essen
and FEhS – Institute for Building Materials Research are working closely
together on the project.