EAF-slags – mainly inert but also interesting?

In direct comparison to steel production using conventional blast furnaces, steel production using electric arc technology is more flexible, more specialised and more environmentally friendly (Swiss Steel Group). It is therefore to be expected that the amount of EAF-slags (Electric-Arc-Furnace-Slags) produced as recyclable "residual material" will increase in the future due to the increasing installation of electric furnaces. EAF-slags (Figure 1) are currently used in the construction industry, wastewater treatment and, to a lesser extent, in the cement industry. These slags can also be used as agricultural fertilisers. The use within cement production includes the substitution of raw meal for clinker production as well as the use in cement and concrete (Teo et al. 2020).

Figure 1: Coarse EAF-slag (Terrones-Saeta et al., 2021)


In terms of cement technological considerations, EAF-slag is predominantly classified as inert, so that in most cases only a small contribution to strength development can be attributed to EAF-slag (Ehrenberg, 2009). Adding 5-10 % EAF-slag to Ordinary Portland Cement can result in a strength development that is comparable to that of Ordinary Portland Cement (Tao et al. 2020).

Chemical analyses of EAF-slags produced worldwide show CaO contents between 16.9 and 50.0%. The magnesium oxide contents range from ~1.5 to 14.0% (Tao et al., 2020). Theoretically, CO₂ can be permanently bound by recarbonation of the oxidically bound mineral phases, which essentially means CaO and MgO. The maximum amount of CO₂ that can be reabsorbed is the CO₂ content emitted during the production of the EAF-slag. Investigations show that it is generally possible to incorporate CO₂ during the grinding of EAF-slag. Due to the generation of high finenesses and new specific surfaces during grinding, a sufficiently high reaction rate can be expected, but cannot yet be quantified more precisely. The boundary conditions (temperature, residence time, etc.) are also still unknown and therefore need to be investigated. EAF-slags could therefore be used in cement and concrete in the future in a climate-neutral way by means of comminution and simultaneously CO₂ binding. Studies show that wet grinding of EAF-slags with the induction of gaseous CO₂ can absorb part of the greenhouse gas. Compared to typical dry grinding - as is commonly used in the cement industry - the recarbonisation effect is considerably higher with wet grinding than in direct comparison to dry grinding (Kurusta et al., 2023; Yokoyama et al., 2010).


How do you deal with the heavy metal concentrations in the EAF-slag?

One problematic aspect in the processing of EAF-slag is the handling of heavy metals, which in the best-case scenario have to be leached out during wet grinding and subsequently be chemically precipitated and disposed. Promising results have already been achieved with regard to the leaching and precipitation of heavy metals in a research project on bypass dust washing. Wet treatment of bypass dusts allows heavy metals of interfering chlorine salts to be washed out so that the cleaned dusts can be fed back into the rotary kiln as a CO₂-reduced component. This process is still part of current research. In general, if technically feasible and with correspondingly reliable results, parallel processing of bypass dusts and EAF-slags as well as post-treatment of the heavy metals is also conceivable.


Swiss Stell Group – Internetauftritt www.dew-stahl.com. Zugriff am 20.11.2023 um 13:41 Uhr.

Teo P.T., Zakaria, S.K., Salleh, S.Z., Taib, M., Sharif, N., Seman, A., Mohamed, J., Yusoff, M., Yusoff, A., Mohamad, M., Masri, M. and Mamat, S., 2020: Assessment of Electric Arc Furnace (EAF) steel slag waste’s recycling options into value added green products: A review. Metals 2020, 10, 1347.

Ehrenberg, A., 2009: Verwendung von Stahlwerksschlacken in der Zementindustrie. ZKG 06/2010.

Kurusta, T., Mucsi, G., Kumar, S. and Kristaly, F., 2023: Carbon-dioxide sequestration by mechanical activation of Linz-Donawitz steel slag; the effect of water on CO2 capture. Fuel 352.

Yokoyama, S., Sato, R., Nik, H.B., Umemoto, M., 2010: Behavior of CO2 absorption in wet-grinding of electric arc furnace reducing slag by vibration ball mill. ISIJ International, Vol. 50, No. 3, pp. 482-489.

Picture credits

Figure 1 Taken from Terrones-Saeta, J., Suarez-Macias, J., Moreno-Lopez, E. and Corpas-Iglesias, F.A., 2021: Determination of the chemical, physical and mechanical properties of electric arc furnace slags and environmental assessment of the process for their use as aggregate in bituminous mixtures. Materials 2021, 14, 782.

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Environment and Plant technology

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