The metals industry is confronted with a twofold challenge of both increasing the production output, so that green energy solutions can play a vital role in the future, while simultaneously decreasing its own CO₂ emissions. To achieve both goals, more focus should be put on metals recycling, increasing the recycling yields and decarbonizing the existing technologies to do so. Current production technologies can present metal losses in the slag and produce significant CO₂ emissions from burning coke for heat and as a reducing agent. A potential solution to both problems is to utilize a submerged electric arc furnace (SAF) which functions both as a settling and reduction furnace. This furnace operates via Joule’s law in which heat is generated via the conversion of electricity via the slag’s resistance.

Recycling and decarburizing current metallurgical processes is key for our planet’s future and for both aspects, digital twinning will play an important role. However, the various modelling techniques being used for digital twinning require a lot of input variables (viscosities, diffusion coefficients and surface energies need to be known as a function of temperature, atmosphere and composition). Unfortunately, there are no full databases for properties such as electrical conductivities and diffusion coefficients, as these data are typically scarce, which in turn is related to the inherent difficulty of determining them experimentally. The need for more and more accurate data regarding physical slag properties is clear and will be extremely valuable in making the simulations quantitative and more realistic.

The high temperature slag properties are difficult to determine, but at the Sustainable Materials Science research group of Ghent University, we focus on determining them via a combined experimental-modelling method. On the modelling side, molecular dynamics simulations are used to investigate oxidic slag physical properties. With MD simulations, one can follow the time evolution of a system (consisting of atoms or molecules) by integrating Newton’s equation of motion. The input for an MD simulation mainly consists of a force field as well as initial positions, velocities, mass and charge of each atom. The determination of the transport properties in existing literature of molecular dynamics simulations in oxidic systems, is typically based on incorrect assumptions. For example, to determine the ionic conductivity, the frequently-used Einstein-Stokes equation fails to take into account all ionic types and neglects correlated motion. Furthermore, the viscosity determination using the Einstein-Stokes formula also assumes independent motion of the different ions.

This is why, for this study, specific attention is given to a proper analysis of the simulations to evaluate the physical slag properties without making a priori assumptions such as independent ionic movement. The electrical conductivity will be calculated according to the more general Einstein relationship. The first results compare different available empirical force fields, which were optimized to describe various systems and properties. A critical comparison with experimental values, both from literature and from our own lab, will be used as validation.

Ferrous metallurgical slag is recognized as one of the precious domestic resources because of its stable amount and quality in Japan, where natural resources are very limited. It has been widely used in various ways such as a cement raw material, artificial stone material, fertilizer, and so on. In particular, the use of blast furnace slag as a cement raw material contributes significantly to reducing CO2 emissions during cement production. In addition, blast furnace slag and steelmaking slag are widely used in the agricultural sector as fertilizer substitutes.

Meanwhile, the rapid transformation of steel production process is expected to promote the decarbonisation in steel manufacturing sector, and it is easy to imagine that the physical and chemical properties and the ratio of ferrous metallurgical slag generated from carbon-free process will dramatically vary from their current situation, resulting in the significant changes in the flow of slags both domestically and overseas.

In this talk, an overview of research and developments on the utilization of ferrous metallurgical slag in Japan so far will be summarized, and the ideal steel manufacturing process and associated ideal slag valorisation to achieve the decarbonisation in the steel sector will be discussed.

Betolar Plc is a pioneering Finnish materials technology company driving the green transition in mining, metallurgy and construction. It was founded in 2016 and is domiciled in Kannonkoski, Finland. Betolar is listed on the Nasdaq First North Growth Market.

Our mission is to help reduce CO₂ emissions and the use of virgin natural resources. Since established, Betolar has developed services to commercialize cement free concrete solutions with low climate impact under Geoprime brand in which metallurgical slags have been played an important role. Key focus is on how to convert the waste / non-utilized materials into usable products with significant value.

There are numerous mineral-based waste side streams like tailings, precipitates and slags in mining and metal industry, which are not utilized and thus, resulting in waste. Reasons for this are multiple, which may hinder their utilization. However, Betolar has recently developed several solutions how to process non-utilized side streams (practically wastes), resulting in generation of valuable products at zero waste.

There are several benefits in our slag valorisation approach: in addition to added value, there is a significant reduction in waste material and required land fill area. Knowledge on slag chemistry, thermodynamics, reducing agents, existing side streams and their mineralogy, chemical composition, among others can make treating the side streams commercially attractive. Some selected examples are presented in this paper.

Against the backdrop of several technological breakthroughs, the valorisation of slag (and other materials) is first and foremost a regulatory challenge. The main focus of this talk is to highlight ongoing trends across Europe (and beyond), both in terms of policies and standards developments. While the future for slag valorisation looks bright in Europe, key hurdles will need to be overcome to accelerate and maximise their deployment in key sectors like cement and concrete.