NuKoS – Utilization of carbon dioxide in slags from steel and metal production

Higher added value of secondary raw materials

The iron and steel industry in Germany produces about 14 million tons of iron and steel slag annually. With a utilization rate of 95 per cent, these products are mainly used in the cement industry and road construction. Within the framework of the research project, CO₂ from various industrial sources will be used to produce higher quality products for different market segments to the applications commonly used today. This includes the production of a highly porous material which can be used as an insulating material or granulate and thus, increases the added value from slags. On the other hand, the project focuses on slags that currently find no application, mainly fine fractions. These originate from their mineralogy by disintegration, or they remain during slag processing and screening. By introducing CO₂, the carbonation properties of the slag are to be used to produce new high-quality building materials or even basic chemicals from these fine fractions. The focus is also on the necessary quality requirements for the CO₂-containing gas.

Practice-oriented development of new methods

The foaming of molten BOF slag by injecting CO₂ is intended to create new, high-quality products. The production of so-called pumice slag has so far only been known from blast furnace slag. Due to the higher iron oxide content of the BOF slag and the crude steel that could run along with it, previously known techniques cannot be used and have to be newly developed due to the risk of explosion. This will be developed in laboratory tests, which will be extended in the project to pilot tests of up to five tons in order to use the slag as a high-quality insulating material in addition to its current applications. To date, the fine fractions deposited are brought to the required particle size distribution by mechanical processing in order to generate finished parts and lightweight aggregates for the building materials and cement industry by carbonation in a second process step. On the other hand high-quality carbonates for other industries as filling material by means of leaching and precipitation are produced. The processes take place in autoclaves, partly under high pressure, on a laboratory scale and will be scaled up to a pre-industrial demonstration-scale within the project. Besides, different CO₂-containing raw gases will be tested.

A win-win situation for the environment

The processing of secondary raw materials into highquality products using CO₂ creates a potential benefit for the environment. The consortium will contribute to interdisciplinary knowledge from different industrial sectors. For the steel industry, ThyssenKrupp Mill Services & Systems and the FEhS Institute will provide materials and develop treatment processes for molten slags. The fine-grained slag fractions will be processed by the LOESCHE company and subsequently analyzed and continued processed by Fraunhofer UMSICHT for various applications. The companies Ruhrbaustoffwerke, Spenner, Wagro Systemdichtungen, and Wolf are involved in the evaluation of the products as well as development and testing on a demonstration-scale. Also, a life cycle assessment of the utilization options and strategic decisionmaking in product and process development is carried out. The results can be used in both integrated and electric steel production, since the developments relate to all iron and steel slags.

Interview about NuKoS

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