Development of an approximation model for the evaluation of slag treatment strategies
Sustainable management of resources and circular economy are key focal points of
research and development activities within the iron and steel industry. In the project Slagreus, a novel approach enhancing internal and external recycling of basic oxygen furnace (BOF) slag has been developed.
Taking advantage of different physical and chemical properties of the slag (e.g. density, solidification properties, magnetic susceptibility or thermal expansion), a primary liquid
iron enrichment process, followed by a secondary solid iron enrichment process, was established to separate the slag into an iron-rich fraction and a phosphorus- and calcium-rich fraction. Accompanying the small pilot and industrial scale tests within the framework of the project, an approximation model for the assessment of the slag treatment was created. The tool has been developed in Microsoft® Excel (including Visual Basic for Application elements) and shall provide information about expected qualities and quantities of the slag fractions as well as overall yield of the pre-treatment processes based on the available BOF slag analysis. Furthermore, it intends to enable plant operators performing parameter studies to get information about a possible treatment of the slag and thus improving BOF slag utilization.
Basic oxygen furnace (BOF) slag is generated during the processing of hot metal to crude steel in the BOF and is an essential metallurgical element of the steel making process. About 120 kg of BOF slag is formed per ton of crude steel, resulting in an annual volume of about 10 Mio tons of BOF slag in the European Union (EUROFER 2021), (World Steel Association 2021). Based on their properties as well as their technical, environmental and legal suitability, slags have various fields of application. Depending on the legal situation of requirements, BOF slag is primarily applied in road construction, whereby minor quantities are used in hydraulic engineering, as cement and concrete additives, in the fertiliser industry or recycled internally. Although BOF slag has considerable potential to be deployed as a secondary raw material, a complete valorisation of BOF slag is currently not viable, due to the volumetric instability/volatility of the free lime in the slag (external recycling) or phosphor content in the slag (internal recycling). Especially considering an enhanced circular economy, efforts are being made to recover and recycle the metal and the mineral fractions of the slag. Therefore, various initiatives have been launched to increase the external and internal utilisation of different types of slags (Algermissen et al. 2017; Burström et al. 2002; Chazarenc et al. 2014; Colla et al. 2017a; Colla et al. 2017b; Pietruck et al. 2016; Stubbe et al. 2013).
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