NuKoS - Utilization of carbon dioxide in slags

CO2 as a sustainable carbon source - ways to industrially utilize slags from steel and metal production

Carbon dioxide in slags

The processes are tested in the high-pressure pilot plant.

Project goals: Increase raw material productivity and minimize CO2

In the "NuKoS" research project, slags from steel production are to be processed for further use with the aid of CO2. The aim is to use the slags to produce higher-value products for the construction, plastics and paper industries. On the one hand, the slags are to be used to produce higher-value products for the construction, plastics, cement and paper industries. On the other hand, the project focuses on slags that currently have no use. In this way, climate-damaging CO2 can be recycled and, at the same time, the amount of materials to be landfilled can be drastically reduced.

Project Benefits: Making byproducts usable as materials

Steel production in Germany generates around 5.5 million metric tons of steel mill slag (SWS) each year. Around 65 percent of this byproduct is already being reused, for example in the production of building materials or fertilizers. 15 percent of the SWS currently remains unused due to its fine grain size, while another 20 percent is temporarily stored for other reasons. There is a lack of highly specialized methods to make these materials usable and to introduce them into an efficient further processing process. For this reason, Fraunhofer UMSICHT and its project partners are researching the following three processes.

CO2 -low-emission building materials

In one method, cement-free building materials such as insulation and construction materials are to be produced from SWS. For this purpose, the molten phase of SWS is to be used to foam it by injecting CO2 in such a way that a porous material with low bulk density is produced - similar to a pumice stone. Such a material could be used, for example, as an acoustic or thermal insulation material.

In another process, solidified, fresh, fine-grained SWS is used. The previously landfilled fine fractions are first brought to the required particle size distribution by mechanical processing such as grinding, sorting and classification. In a second step, new high-quality basic materials for the construction industry can then be produced by carbonation using compressed carbon dioxide - for example cement-free, low-CO2 -emission prefabricated building components and bulk insulation based on SWS.

In a third method, new processes are being developed to produce calcium carbonate from SWS for further processing in the paper industry, for example. For this purpose, solidified SWS, which are technically unsuitable for road construction and are currently not recycled due to their inferior physical properties, are used.

Project partners

  • Spenner GmbH & Co KG
  • ThyssenKrupp MillServices & Systems GmbH
  • Robert Josef Wolf GmbH & Co.KG
  • Ruhrbaustoffwerke GmbH & Co KG
  • WAGRO System Gaskets Ltd.
  • FEhS - Institute for Building Materials Research e.V.

Funding information

Federal Ministry of Education and Research


Duration: February 2020 until March 2023

Funding code: 033RC027