Research and Development

Use of Slag for Energy Recovery in the Local District Heating Network (SchlaGie)

The SchlaGie research project was launched in April 2025. The objective of this three-year initiative is to develop and validate an innovative heat recovery concept for slag beds, enabling the utilization of industrial waste heat generated during iron and steel production. By unlocking a previously untapped energy source, the project aims to make a significant contribution to the decarbonization of heat supply in the building sector.

Background and Relevance

Particularly in the Ruhr region, Germany’s largest urban agglomeration, the pressure to develop climate-neutral heating solutions continues to increase. In light of the German Federal Government’s ambitious target of achieving greenhouse gas neutrality by 2045, the transition to alternative, non-fossil energy sources is essential.

One key opportunity lies in the utilization of industrial waste heat, which remains largely untapped. Of particular interest is the waste heat contained in molten slag, a by-product of steel production. After tapping, the slag is deposited in large slag beds, where it cools over an extended period. During this process, a substantial amount of thermal energy is dissipated into the environment without being utilized.

Potential and Impact

Using steelworks slag in Duisburg as an example, the theoretical recoverable heat potential amounts to approximately 280,000 MWh per year, even when assuming a conservative recovery rate of only 50% of the maximum available energy. This corresponds to a potential reduction of up to 56,000 tonnes of CO₂ emissions annually, based on natural gas as the reference fuel.

Targeted recovery of this heat therefore offers not only environmental benefits but also significant economic value. It improves the energy efficiency of steel production while simultaneously supporting municipal heat planning through a reliable and locally available source of thermal energy.

Project Objectives and Expected Outcomes

The SchlaGie project pursues several strategic objectives:

• Development of a technical concept for the recovery and transfer of heat stored in slag beds.

• Assessment of the economic feasibility and transferability of the concept to other locations and slag types.

• Integration into existing or planned district heating networks to supply new sustainable residential developments and infrastructure projects.

• Strengthening regional value creation and supporting the low-carbon transformation of industry.

By linking industrial processes with municipal heat planning, SchlaGie contributes to improving the security of supply of climate-friendly heat. This represents a key building block on the path toward climate-neutral urban development in North Rhine-Westphalia and beyond.

Contact:

Dr. rer. nat. Michael Dohlen

Partners:

C-Technik GmbH

FEhS – Institute for Building Materials Research

Fraunhofer UMSICHT

THGA – Georg Agricola University of Applied Sciences

Funding:

Funded by the European Union and the State of North Rhine-Westphalia under the ERDF/JTF Programme North Rhine-Westphalia 2021–2027.

Resource-Efficient Masonry Units with a Reduced Carbon Footprint (AACtion)

The AACtion research project was launched in May 2025. The three-year initiative aims to make construction materials such as autoclaved aerated concrete (AAC) and calcium silicate masonry units more environmentally friendly. One key approach is the use of secondary raw materials, such as steelmaking slags, to replace conventional cementitious binders and primary raw materials. This is expected to significantly improve the carbon footprint of the construction sector.

The project is funded through the “Industrie.IN.NRW” innovation competition as part of the ERDF/JTF programme of the State of North Rhine-Westphalia. It makes an important contribution to achieving the United Nations Sustainable Development Goals (SDGs), particularly in the areas of climate action (SDG 13) and responsible consumption and resource use (SDG 12).

Sustainable construction is of particular importance in North Rhine-Westphalia, especially in the Ruhr region, Germany’s largest metropolitan area. Today, around 75% of the population lives in urban areas, further increasing the demand for environmentally sustainable housing and infrastructure.

Innovative Building Materials for the Future

The project focuses on the further development of steam-cured masonry products such as autoclaved aerated concrete and calcium silicate units. By replacing conventional binders and raw materials with industrial by-products such as slags, it is possible not only to reduce CO₂ emissions but also to significantly improve resource efficiency.

In addition, existing manufacturing processes will be optimized with the aim of reducing energy consumption and increasing the use of renewable energy sources. In this way, the project supports the construction industry in taking an important step towards achieving the objectives of the 2030 Agenda for Sustainable Development.

A distinctive feature of the project is the close collaboration between research institutions, regional networks, and industry partners. Universities and research organizations contribute their technical expertise, while small and medium-sized enterprises (SMEs) and industrial partners provide practical know-how and production capacities. This strong cooperation ensures that the solutions developed are both practical and readily implementable.

Contact:

Dr. rer. nat. Michael Dohlen

Partners:

Fraunhofer-Institut für Bauphysik IBP

Xella Technologie- und Forschungsgesellschaft mbH

SCHLENK Metallic Pigments GmbH

HDB Recycling GmbH

Heinrich Temmink GmbH & Co. KG 

Ingenum GmbH 

Funding:

Funded by the European Union and the State of North Rhine-Westphalia under the ERDF/JTF Programme NRW 2021–2027.

Geometallurgical Processing of Steelmaking Slags for the Circular Recovery of Critical Raw Materials and CO₂ Sequestration (GeoCRM)

The GeoCRM research project commenced in October 2025 with a duration of three years. Its objective is to develop process routes based on geometallurgical analyses that enable the efficient recovery of iron oxide as well as critical raw materials such as phosphorus, vanadium, and chromium. At the same time, the remaining calcium silicate fraction will be processed for utilization as a CO₂ storage medium and as a feedstock for construction materials.

Research Focus Areas

The project is structured into six core work packages:

1. Geometallurgical Characterization

Development of an evaluation framework based on characteristic material properties to enable the holistic utilization of basic oxygen furnace (BOF/LD) and electric arc furnace (EAF) slags, including the contained critical raw materials (V, P, Cr).

2. Mechanical Processing

Development and testing of suitable processing methods for the production of pre-concentrates for subsequent metallurgical treatment.

3. Metallurgical Processing

Investigation of the recovery potential of vanadium, phosphorus, and iron through hydrometallurgical and pyrometallurgical process routes.

4. Utilization of Metallurgical Residues

Identification of utilization pathways to minimize waste generation and support the implementation of a sustainable circular economy.

5. Environmental and Economic Assessment

Comprehensive evaluation of the entire process chain, considering material composition and external boundary conditions.

Continuous Development of the Utilization Concept

6. Funding and Project Partners

The project is funded by the European Union and the Ministry of Economic Affairs, Industry, Climate Action and Energy of the State of North Rhine-Westphalia (NRW) under the ERDF funding initiative “Green Economy.IN.NRW”.

As part of the research project, thyssenkrupp MillServices & Systems provides a representative set of sample materials together with the corresponding physical and chemical analyses. A further focus is the analysis and evaluation of economic and environmental process performance indicators.

The VDEh-Betriebsforschungsinstitut (project coordinator) is responsible for the planning and execution of the hydrometallurgical and pyrometallurgical processing routes. In addition to the practical investigations, the process data generated from these metallurgical treatment routes are evaluated with regard to the overall process concept.

RWTH Aachen University (AMR) is responsible for the mechanical processing of the slag based on insights gained from the geometallurgical analyses, as well as for the evaluation of process data generated during the mechanical processing trials.

FEhS – Institute for Building Materials Research is responsible for the geometallurgical analyses and the evaluation of process data with respect to geometallurgical assessment.

Co-reactive focuses on the development of a process for CO₂ sequestration and the simultaneous production of construction materials using the calcium silicate fraction obtained from the processed steelmaking slag.

Contact

Dr. rer. nat. Michael Dohlen

Project Partners:

VDEh-Betriebsforschungsinstitut GmbH

RWTH Aachen University - Lehr- und Forschungsgebiet Technologien zur Aufbereitung mineralischer Rohstoffe (AMR)

FEhS – Institut für Baustoff-Forschung e.V.

Co-reactive GmbH

Funding:

Funded by the European Union and the State of North Rhine-Westphalia under the ERDF/JTF Programme North Rhine-Westphalia 2021–2027.

Deconstruction of Construction Waste and Excavated Soil Landfills (RueBe)

The RueBe research project was launched in November 2025 under the BMFTR funding initiative “Resource-Efficient Circular Economy – Urban Mining”.

The objective of the project is to recover mineral waste from DK0 landfills and reintegrate it into sustainable construction material cycles.

DK0 landfills represent a largely untapped resource potential:

• More than 15 billion tonnes of excavated soil and construction waste (as of 2022)

• Significant importance as anthropogenic raw material reservoirs

• High potential for resource conservation and CO₂ reduction

The project focuses on the complete utilization of landfill materials through:

• Wet-mechanical treatment (soil washing) to remove contaminants and unwanted materials

• Recovery of coarse and fine fractions as secondary raw materials

• Application in various construction products, such as alternative binders, controlled low-strength materials (flowable fills), and masonry bricks

In parallel, the legal and regulatory framework is being analyzed to facilitate the use of recycled materials in the construction sector.

To evaluate the developed solutions, the project includes:

• Environmental and economic assessments

• Development of concepts for the further recycling of recycled-material-based construction products

• Evaluation of market potential and industrial feasibility

The project consortium covers the entire value chain, from raw material recovery and material processing to material development and industrial-scale construction product manufacturing. This integrated approach ensures that all project activities and outcomes remain focused on achieving rapid market implementation and commercial utilization.

RueBe makes an important contribution to resource conservation and the advancement of a sustainable circular economy in Germany. The project results have the potential not only to increase recycling rates for mineral waste but also to enable landfill operators to develop new business opportunities.

Contact:

Dr. rer. nat. Michael Dohlen

Partners:

Fraunhofer-Institut für Bauphysik IBP (Projektkoordination)

Dyckerhoff GmbH

Schlagmann Poroton GmbH & Co. KG

Wilhelm Geiger GmbH & Co. KG

Technische Universität München

Universität Augsburg

Bundesverband Sekundärrohstoffe und Entsorgung e. V.

Funding:

Funded by the BMFTR program “Resource-Efficient Circular Economy – Urban Mining” and administered by Project Management Jülich (PtJ).