Sustainable sLag process to obtain a valuable METAL

STILLMETAL project develops a sustainable process to convert foundries slag into ferroalloys. It solves the problem of slag landfill disposal, transforming a cost into a revenue and increasing competiveness and independence from raw materials supply. Know-how belongs to OPIGEO (SME specialized in slag valorisation), to UNIPD and ZAG, whereas ITALGHISA (SME ferrolloys leading supplier) possesses trade secret. ZEROCENTO will be the 1st customer building the industrial plant (TRL9). Cast iron foundry companies produce an average of 1.000 tons/year of slag (500.000 tons/year in Italy; 5 million tons/years in Europe) that’s now disposed of in landfill with a cost of 25€/tons. The project aims to valorise the slag through a process, sustainable from both technical and economical point of view, able to transform it into valuable materials. This process involves the reaction at high temperatures, in the molten state, between the slag and specific added materials to give a metal and a residual oxide slag. The added materials are either home or new or old scraps rich in Si and old scraps of Al. The obtained metal has a composition of a Ferroalloy, a valuable alloy of iron with silicon, that can be sold or reused inside the same foundry for the production of new cast iron, whereas the residual oxide slag, despite being a slag, possesses a right composition, a mix of oxides of aluminium, silicon and alkali, to have a market value for ceramic and/or cement industry. The process has already been tested at TRL5 and during the project a process at TRL9 will be realized and installed in a cast iron foundry. The process will contribute to improve both the cost saving (reducing to zero the waste management) and the resource and energy efficiency (producing ferroalloy from slag) of cast iron foundries.

The STILLMETAL project makes an important contribution to scientific progress by introducing a new, research-based approach to treating foundry slag as a valuable secondary raw material. It expands the scientific understanding of high-temperature reduction reactions in complex oxide systems and advances knowledge in the field of sustainable metallurgy. The validation of the process from TRL5 to TRL9 in a real industrial environment provides rare data on the behaviour of molten materials in practice, strengthening the reliability of theoretical and thermodynamic models. At the same time, the project demonstrates that high-quality ferrosilicon alloys can be produced from non-traditional, waste-based sources, opening new research directions in circular economy and materials science. STILLMETAL therefore represents a significant scientific breakthrough towards the complete mineral-metal recovery of waste and the development of low-carbon technologies.

The STILLMETAL project has significant strategic importance for Slovenia’s development, as it strengthens the technological independence of domestic foundries and steel industry by enabling them to convert slag into their own ferrosilicon alloys instead of disposing of it. This reduces dependence on imported raw materials and improves competitiveness. The project also supports the creation of high-tech jobs and fosters domestic expertise in advanced metallurgy and the circular economy. By eliminating slag disposal, STILLMETAL contributes directly to Slovenia’s environmental goals, reducing the use of primary resources and supporting industrial decarbonisation. It thus represents a strong example of industrial innovation that connects science and industry and reinforces the country’s long-term sustainable and technological development.