Project in the Spotlight: From Research to Patent – Collaborative Efforts Unlock the Potential of BOF Slag as Building Material

Key information

Project title: Mitigating BOF slag-leaching of oxy-anions Vanadate, Chromate, Molybdenate
Project in the Spotlight: T22019
Funding: PPS Allowance 2022
Run time: 2023-2024
Market: Circularity/sustainability and Civil

Written by M2i Program Manager: Viktoria Savran

The growing demand for sustainable construction materials has driven innovative research initiatives worldwide. One such groundbreaking project, carried out within the M2i program, focused on unlocking opportunities for repurposing Basic Oxygen Furnace (BOF) slag as a cement-like binder, simultaneously addressing the leaching behavior of this industrial byproduct. Led by researcher Yanjie Tang under the supervision of Dr. Katrin Schollbach, Assistant Professor, and Prof. Jos Brouwers at Eindhoven University of Technology’s Department of the Built Environment, the project marks a major advancement. With support from industrial partner Sieger van der Laan of Tata Steel, it tackles the environmental challenges associated with BOF slag in construction applications.

The Challenge of BOF Slag
BOF slag is a byproduct generated during steel production, with approximately 100 kilograms produced per ton of steel. While its mineralogical similarities to Portland cement clinker make it an attractive alternative for building materials, the leaching of potentially toxic components such as vanadate, chromate, and molybdate has hindered its application. These oxy-anions become particularly mobile after CO2 exposure of the slag, raising environmental concerns. To mitigate this issue, the project explored phosphate-based activation methods to enhance BOF slag’s binder properties obtained by hydration (like cement) while immobilizing harmful elements, thus ensuring compliance with regulatory standards.

Breakthrough innovation
The research produced innovative advancements in optimizing BOF slag behavior through studying its activation with a continuous spectrum of potassium phosphates, from KH2PO4 (MonoKP) to K3PO4 (TriKP), imposing a range of conditions from acidic to basic during hydration. In general, the phosphate salts significantly improved the extent of reaction of C2S, the major BOF slag phase, forming beneficial phases such as C-S-H gel, hydrogarnet, and hydroxyapatite, yielding product strength and immobilizing heavy metals. Acidic endmembers (MonoKP), showed strong reaction but resulted in too high porosity of the building product. Dipotassium hydrogen phosphate (DiKP) (at ~2wt% of slag addition) proved to be the optimal activation, offering exceptional resistance to carbonation and stabilizing the material’s pH, thereby effectively immobilizing harmful elements like vanadium, chromium, and molybdenum in compliance with Dutch Soil Quality Decree standards. The insights gained provide better control over the activation process, paving the way for optimized and sustainable applications. These innovations led to the patent application titled “Method for Activating Basic Oxygen Furnace Steel Slag” (WO2024/052265A1), which protects the activation processes and formulations developed through this research.

Industrial Impact and Sustainability
The project’s findings highlight BOF slag’s potential as a cost-effective and environmentally friendly alternative in construction. Unlike conventional cement production, which generates significant CO₂ emissions, phosphate-activated BOF slag offers a sustainable solution that leverages existing production facilities with minimal additional investment. Applications of this novel material span precast concrete elements, paving blocks, and waste containment systems. The enhanced durability, mechanical properties, and environmental compliance make it ideal for demanding conditions, and for extending the service life of ordinary cement-based concrete by applying it as a carbonation resistant coating (render) aligning with global sustainability goals.

Collaborative Effort and Future Directions
This project demonstrates the power of collaboration between academia and industry. The involvement of Tata Steel ensured a direct link to industrial needs, while the academic rigor of TU/e’s Built Environment Department provided a solid foundation for innovation. Looking ahead, the research team envisions scaling up to mortar and concrete applications, optimizing particle packing using slag based sand and aggregate to enhance overall performance and creating a 100% slag-based product. Furthermore, exploring options for extending the activation by including other additives could offer even more economical and efficient solutions.

The project T22019 got PPS funding in 2022. Project partners are grateful to Dutch government for providing financial support.
For more information about the project or collaboration opportunities, please contact M2i, the Materials Innovation Institute. Together, let’s build a sustainable future.

Yanjie Tang, Eindhoven University
“As a researcher, I am happy to see our work on phosphate activation of BOF slag yielding such promising results. This project allowed us to not only enhance the material’s hydration and mechanical properties but also address critical environmental challenges by effectively immobilizing heavy metals. The recognition of our efforts through the patent application WO2024/052265A1 underscores the potential of this innovation to drive sustainable solutions in the construction industry.”

Katrin Schollbach, Eindhoven University
“Supervising this project has been an inspiring journey, as it represents a perfect synergy between scientific innovation and practical application. Yanjie’s innovative work on phosphate activation of BOF slag not only addresses critical environmental challenges but also aligns closely with the needs of industrial partner, Tata Steel.”

Sieger van der Laan, Tata Steel
“At Tata Steel, we are always looking for innovative ways to repurpose by-products like BOF slag in a sustainable and cost-effective manner. This collaboration with TU/e and Yanjie Tang has provided us with a deeper understanding of how phosphate activation can unlock the potential of BOF slag as a high-performance construction material. The project solved a critical issue with slag use, by improving its environmental performance, and creating value-added applications. This Tata Steel sponsored research project is an example of our commitment to sustainability and circularity in the steel industry.”