Closing the loop of raw material flows through a circular economy and thereby finding sustainable refractory solutions is one fundamental strategic pillar of RHI Magnesita. In the last years, a major effort has been undertaken to translate this approach into gunning mixes. The main challenge was to implement a significant amount of circular raw materials, while keeping the main properties of the gunning mixes on the same level, for example the refractory performance, adhesive properties, and machinery handling. By following these criteria in a systematic development process, it has been possible to create a new sustainable gunning mix portfolio with a reduced product carbon footprint of up to 85%. In an intense and comprehensive trial phase in the main steel producing units, namely electric arc furnaces, basic oxygen furnaces, and ladles, it was possible to fully prove this new refractory concept.
With the targets of increasing sustainability and substantially reducing CO2 emissions, RHI Magnesita entered into a joint venture with Horn & Co. Group, the industry leader when it comes to circular material processing. This partnership called MIRECO positions RHI Magnesita as a pioneer in circular economy solutions for the refractory industry. Both companies have been working together for many years, with RHI Magnesita having purchased the majority of its circular raw materials from Horn & Co. Group. As a result, a close and trustful relationship evolved over time, forming an ideal basis for a joint and sustainable future. This was a crucial step to pave the way towards RHI Magnesita’s ambitious global target of achieving a 15% CO2 emissions reduction by 2025, as amongst other measures the usage of circular materials significantly impacts this area. In this article factors that influence incorporating circular refractory materials in basic gunning mixes are discussed as well as the approaches taken to develop the new sustainable product portfolio.
To provide increasing customer transparency, RHI Magnesita is calculating the product carbon footprint (PCF) of its refractory products and has implemented this information on the technical data sheets. All emerging greenhouse gases are considered in these calculations, starting with the raw material extraction, followed by transportation, production, and packaging. Furthermore, the indirect emissions from the electricity used and externally purchased raw materials are included in the calculations—namely scope 1, 2, and 3 emissions. The so-called cradle-to-gate approach adopted excludes the final transportation from RHI Magnesita’s production plants to the customer.
Once the refractory products have been shipped, this PCF can be considered as scope 3 emissions at the customer site. This means that the emissions value RHI Magnesita delivers can serve as a basis for further calculations in for example a steel plant, which will continue to gain importance in the near future. The PCF of our products will be reevaluated and recalculated on a regular basis.
Up to now, the predominant opinion was that the wetting behaviour of circular MgO-C raw materials makes it impossible to use them in basic gunning mixes because of the negative effect on processing due to a low setting speed and initial adhesion. Therefore, a complete reexamination was required, including fundamental investigations on how circular materials could be implemented into basic gunning mixes.
The first approach to increase the gunning mix sustainability was to use leftovers that would otherwise have been landfilled. Therefore, detailed research on different material sources was performed to obtain a holistic overview of the chemical composition, including impurities. Additionally, microscopic investigations were carried out to gain information about the microstructural properties and the bonding structure, for example:
From these investigations it could be concluded that the loss on drying (LOD) was relatively high, (i.e., up to 12%), and there was a huge variation in the main oxides such as MgO, CaO, SiO2, and Al2O3, as well as the carbon content between different samples. However, the amount of heavy metals was negligible and no hexavalent chromium (Cr6+) could be detected. After these investigations, the first test specimens were prepared to enable investigations on the final product characteristics. These specimens were based on the standard silicate-bonded ANKERJET GW gunning mix series and contained either very low or low addition of two circular raw material sources and different grain fractions. Reference specimens were prepared with the standard recipe for comparison.
To achieve RHI Magnesita’s goal of further reducing the carbon footprint of its products, another project was launched to find additional sources of circular raw materials suitable for basic gunning mixes. After considering all the important raw material factors, such as a stable chemical composition, a LOD below 1%, cost efficiency, and a secured supply chain in terms of availability and on-time shipment, it was decided to start an in-depth investigation of magnesia spinel circular material and its potential usage in refractory mixes.
The first step to investigate three different magnesia spinel types was the setting test, which determines the strength, setting behaviour, and temperature development when water is added to the gunning mix. In the initial approach, a 50/50 blend of the different magnesia spinel types with original raw materials was prepared, and the test was carried out on both a silicate- and a phosphate-bonded mixture. During these trials, there was no evidence that the magnesia spinel circular raw materials were detrimental, as all the relevant properties were within the known specifications.
Subsequently, different specimens were prepared that contained a medium and high proportion of magnesia spinel circular raw material in both silicate- and phosphate-bonded versions. To understand the processes induced by heat, the samples were exposed to different temperatures. These tests showed that the physical properties of the samples were not negatively affected when compared to the standard mixture, and although different levels of circular material addition showed different characteristics, no exclusion criteria were identified.
Due to the intense R&D activities, it was possible to implement completely new product types in the gunning mix portfolio, based on different amounts of MgO-C or magnesia spinel circular material. These solutions are paving the way towards a more sustainable future, by decreasing RHI Magnesita’s scope 1 CO2 equivalent (CO2e) emissions, as well as customers’ scope 3 emissions. Another aspect that increases the sustainability is being able to serve the European market with products produced in Europe—local for local—as the gunning mix product portfolio is currently available from the production plant in Veitsch.
Based on detailed R&D, RHI Magnesita has implemented completely new product lines for basic gunning mixes that are paving the way towards a more sustainable future. Through this new but well-established portfolio, customers are able to choose refractory products with lower PCFs and thereby minimise their scope 3 emissions. Due to the continuously increasing demand, RHI Magnesita is working on expanding these product lines to the production plant in Eskisehir (Turkey), thereby enabling further markets to be supplied with regional and sustainable products. To exploit the full potential of circular materials, additional investigations will be performed to determine the capabilities and limits of use, which will lead to an ever-growing sustainable product portfolio for basic gunning mixes as well as other refractory products.
 Lammer, G., Jandl, C. and Zettl, K. Maintenance Matrices: Overview of Common Refractory Maintenance Methods for BOFs and EAFs. Millennium Steel. 2013, 61–65.
 Mosser, J. and Siegl, W. High Lime Gunning Mixes for BOF and EAF. IREFCON 96: 2nd India International Refractory Congress, New Delhi, India, Feb. 8–9, 1996.
 Petio, F. Top Quality Gunning Mixes for BOF, EAF and Ladles. Proceedings of UNITECR 97, New Orleans, USA, Nov. 4–8, 1997.
 Siegl, W. High Quality Gunning Mixes for BOF and EAF. 9th Intercompany Conference, Japan, Nov. 23–28, 1995.