Ladle metallurgy stainless steel slag as a raw material in Ordinary Portland Cement production: a possibility for industrial symbiosis
Introduction
Cement production approaches 3700–4000 Mt/y (U.S. Geology Survey, 2013), corresponding to a substantial CO2 footprint. Considering the process of cement clinker production, half of the carbon footprint originates from the dissociation of limestone during clinkering, whereas the other half is due to fuel combustion. This accounts for about 8% of global CO2 emissions according to the latest 2012 report (Olivier et al., 2012). As a consequence, both the industry and academia are exploring strategies to minimise and/or capture CO2 emissions and a wide portfolio of options appear feasible (Benhelal et al., 2013, Brunke and Blesl, 2014, Gao et al., 2014, Ishak and Hashim, 2014). One of the paths with great potential involves the use of alternative raw materials, preferably Ca-bearing so as to minimise the use of limestone, and the above may become more realistic and sustainable in an industrial symbiosis context (Ammenberg et al., 2014). Examples of industrial symbiosis already exist for decades, the use of ground granulated blast furnace slag and that of fly ash from coal-burning power plants, being two of the most well established. In the paper herein, a new proposal is put forward, aiming to widen the envelope of possibilities.
Stainless steel slags include EAF (Electric Arc Furnace), AOD (Argon Oxygen Decarburization) and LM (Ladle Metallurgy) slags. The last two types of slag are generated during the refining process step in stainless steel making. Stainless steel slag (EAF S – stainless slag) is registered at the European Chemicals Agency (CAS 91722-10-0; Einecs 294-410-9; submission number HQ948325-18) as non-hazardous waste. However, their status in Belgium, Flanders region, is somewhat different. For two specific applications (use in concrete and in asphalt concrete), EAF S slag has the status of raw material instead of waste (Ministrieel besluit, 2012). The quantity of stainless steel produced worldwide in the first half of 2012 accounts to 17.2 Mt (International Stainless Steel Forum). It is estimated that the slag/steel ratio is around 0.33 (tslag/tsteel) (Durinck, 2008). Both the AOD and LM generated slags consist of a high content in CaO, SiO2, MgO but also some Cr2O3 and fluorine (F). The crystalline phase composition is mainly C2S, especially in γ-polymorphic form, with lower levels of merwinite, bredigite, cuspidine and periclase (Kriskova et al., 2012). The major problem with LM slags is the high content in γ-C2S which is less dense than the other polymorphs of C2S. This phase causes a volume increase of about 12% on cooling, generating a voluminous powder; this phenomenon is known as dusting (Taylor, 1990). An important issue resulting from this transformation is the disposal and downstream utilisation of stainless LM slag.
Both cement and steel industries take action to address their environmental footprint. The former, according to the EU ETS (EU Emissions Trading Scheme), aspire to reduce the overall emissions by at least 20% by 2020 and 50% by 2050, compared to the 1990 levels (European Commission, 2008). With respect to the latter, the amount of steel slag produced in 2010 accounts to approximately 21.8 Mt (The European Slag Association, 2012). From this amount, only 6% was used in cement production, 48% for road construction and the rest was deposited or used for other purposes. The challenge lies in the development of integrated, “zero-waste” flow sheets, which recover both metals and utilise the various residues into building applications.
Considering the above, a push and pull scheme appears possible for the metallurgical and cement industrial sector, where residues from metallurgies could become raw materials for the cement industry. Conceptually, this is an example of industrial symbiosis and has been happening for years, e.g. ground granulated blast furnace slag. The use of other slags however does not appear to be straightforward, as presented below for the case of EAF, AOD and LM slags from stainless steel production.
In an overview with respect to the utilisation of EAF and AOD slags from the stainless steel industry (Huaiwei and Xin, 2011) claim that these slags can be very stable on a long term after a stabilisation/solidification process, being further suitable for utilisation in cement production, road construction, civil engineering work. Moosberg-bustnes (2004) has investigated the properties of AOD slag as a filler in concrete. The results revealed a clear potential, provided some of the negative aspects such as activation (effect on cement hydration) and durability can be overcome. Manso et al. (2006) and Pellegrino et al. (2013), find EAF slag suitable as aggregate in concrete production with better or comparable mechanical properties when compared to a reference sample, if the substitution of the aggregate is lower than 50 wt%. Kriskova et al. (2012) have shown that the hydraulic properties of AOD and LM slag can be enhanced through mechanical activation. More work in this area has in fact demonstrated that both mechanical and alkali activation of LM slag appears to be a promising path for delivering an alternative binder (Kriskova et al., 2014, Muhammad et al., 2014). Maslehuddin et al. (2011) have used EAF dust as replacer of 2 wt% OPC in blended cements, indicating improved mechanical properties and durability in their studies. Xuefeng and Yuhong (1998) and Hilton (1998) have also used stabilized EAF dust as raw material in clinker cement production. To the best of our knowledge, there is no work available regarding the utilisation of LM slag as raw feed material in clinker production.
The envisaged work therefore explores an alternative path which seeks to overcome some of the existing issues of the stainless steel and cement industry. The production of OPC cement clinker with addition of 6 wt% and 14 wt% of the fine fraction of LM slag is investigated. A benchmark sample was also produced for comparison. The central aim was to understand the influence of LM slag in the clinkering process, on the microstructure of clinker, on the mechanical and physical properties of the final cement mortars as well as on the environmental performance of these new cements.
Section snippets
Characterisation of raw materials
The raw materials used in this study were LM slag fraction below 160 μm (called also “the fine fraction”), limestone, flysch and bauxite residue (red mud). The fine fraction of LM slag amounts to about 73 wt%, and it has been used as received. This was determined by sieving approximately 50 kg of a representative batch of LM slag. To investigate the variation of slag chemistry for different particle sizes, the LM slag was sieved at different fractions and characterised. The chemical analysis (
Characterisation of the raw materials
The chemical composition of raw materials is presented in Table 1, Table 2, the particle size distribution of the received slag (fraction < 160 μm) in Fig. 1, XRD patterns in Fig. 2 and the QXRD in Table 3.
Limestone was used as main source of CaO (∼54 wt%), flysch for SiO2 (∼58 wt%) and Al2O3 (∼14 wt%), whereas bauxite residue for compensating the needs of Al2O3 and Fe2O3 in the raw meal. The fine fraction of LM slag consisted mainly of CaO (∼56 wt%) and SiO2 (∼32 wt%), which will result in
Environmental aspects and a conceptual process
The motivation to introduce LM slag for clinker production was to reduce the environmental footprint of two industrial processes without compromising the quality of the final product. In the current work, the suggested industrial symbiosis approach has as follows: a) the steel company after the coarse sieving (Table 2), keeps the metal-rich fraction and supplies the metal-poor, dicalcium silicate-rich one to the cement company; and b) the cement company takes the reject of the steel company,
Conclusions
In the transition towards more sustainable industrial processes, incremental, gradual changes that address a range of technical and non-technical considerations appear to be a realistic path forward. Aspiring to contribute to the above, a process was suggested herein that has the potential to become industrially realistic, in the framework of industrial symbiosis. In detail:
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The utilisation of LM slag as a raw material in Ordinary Portland Cement production was feasible at 1450 °C.
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The addition
Acknowledgements
Dr. Angeliki Christogerou and Dimitra Koumpouri from University of Patras, Greece, are acknowledged for their contribution in the production of cement clinker and in the thermal analysis of the raw meals. Dr. Annelies Malfliet from KU Leuven, Belgium, is acknowledged for her contribution in EPMA-WDS analysis. The EPMA-WDS work has been feasible due to the support of the Hercules Foundation (project ZW09-09). Y. Pontikes is thankful to the Research Foundation – Flanders for the post-doctoral
References (49)
- et al.
Global strategies and potentials to curb CO2 emissions in cement industry
J. Clean. Prod.
(2013) - et al.
Energy conservation measures for the German cement industry and their ability to compensate for rising energy-related production costs
J. Clean. Prod.
(2014) - et al.
An overview for the utilization of wastes from stainless steel industries
Resour. Conserv. Recycl.
(2011) - et al.
Effect of mechanical activation on the hydraulic properties of stainless steel slags
Cem. Concr. Res.
(2012) - et al.
Influence of mechanical and chemical activation on the hydraulic properties of gamma dicalcium silicate
Cem. Concr. Res.
(2014) - et al.
Durability of concrete made with EAF slag as aggregate
Cem. Concr. Compos.
(2006) - et al.
Effect of electric arc furnace dust on the properties of OPC and blended cement concretes
Constr. Build. Mater.
(2011) - et al.
Heat of hydration of high reactive pozzolans in blended cements: Isothermal conduction calorimetry
Thermochim. Acta
(2005) - et al.
Properties of concretes with Black/Oxidizing electric arc furnace slag aggregate
Cem. Concr. Compos.
(2013) - et al.
Chromium behavior during cement-production processes: a clinkerization, hydration, and leaching study
J. Hazard. Mater.
(2011)
Characterization of cement minerals, cements and their reaction products at the atomic and nano scale
Cem. Concr. Res.
The existence of amorphous phase in Portland cements: physical factors affecting Rietveld quantitative phase analysis
Cem. Concr. Res.
Utilization of ferroalumina as raw material in the production of ordinary Portland cement
J. Hazard. Mater.
Solidification/stabilization of Cr(VI) with cement: leachability and XRD analyses
Cem. Concr. Res.
Improving the CO2 performance of cement, part III: the relevance of industrial symbiosis and how to measure its impact
J. Clean. Prod.
Standard Test Methods for Chemical Analysis of Hydraulic Cement
Structure and Performance of Cements
Innovations in Portland Cement Manufacturing
High Temperature Processing of Metallurgical Slags: a Method to Promote Recycling
Effect of Mineralizers in Cement Production, Advanced Cementing Materials, Reduced CO2 – Emission
EU Action against Climate Chage. Leading Global Action to 2020 and beyond, Luxembourg
EN 196-1, Methods of Testing Cement – Part 1: Determination of Strength
EN 196-3, Methods of Testing Cement – Part 3: Determination of Setting Time and Soundness
2003/53/EC of the European Parliament and of the Council
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