The decarbonisation of the steel and cement industry is of utmost importance in tackling climate change. Hence, steel production in modern integrated steel mills will be shifted towards electric arc furnaces in the future, in turn causing dwindling supplies of blast furnace slag, which is used as a supplementary cementitious material inter alia to reduce the CO₂ emissions of cement production. Achieving a sustainable circular steel and building material economy requires the valorisation of currently landfilled steel slags and investigating utilisation options for electric arc furnace slag, which is increasingly being generated. For this purpose, different metallurgical residues and by-products were treated by carbothermal reduction in an inductively heated graphite crucible and then rapidly cooled by wet granulation, yielding a slag fraction similar to granulated blast furnace slag and a metal fraction valuable as a secondary raw material. A spreadsheet-based model was developed to calculate residue combinations to accomplish target compositions of the slag and metal fractions to fulfil previously identified requirements of the targeted cementitious and ferrous products. The results demonstrate the high accuracy of the model in predicting the properties (e.g. main oxide composition) of the generated slag and metal fraction, which fulfil the needed requirements for their use as (i) a supplementary cementitious material and (ii) a secondary raw material in steel production.

Mineral wool is commonly used in construction as thermal insulation material. After the product’s lifetime, it is classified as hazardous waste if no trademark of the European Certification Board for Mineral Wool Products (EUCEB) or the German Institute for Quality Assurance and Labelling (RAL) exists. Mineral Wool Waste (MWW) is typically landfilled in Europe, which is challenging due to its low bulk density and dimensional stability. This circumstance highlights the need for alternative recycling methods that increase the recycling rate of construction and demolition (C&D) waste. This article outlines the recycling opportunities of MWW and focuses on the use of thermochemical treatment of different mixtures of input materials to produce a supplementary cementitious material (SCM). The material characterisation results and investigations on the binder suitability demonstrate that the slag fractions after the thermochemical treatment are well-qualified to be used as reactive binder components. Additionally, a material flow analysis was conducted to estimate the substitution potential of MWW as SCM in the Austrian cement industry.

Advancing material efficiency in the steel and cement industry is essential for achieving climate goals. One approach to addressing this is to increase the provisioning of alternative reactive binder materials from residues, in this case, from the steel industry. Different mixtures of identified residues are evaluated for metal recovery and suitability as supplementary cementitious material. For this purpose, suitable combinations are modeled according to specified quality requirements from the cement industry. These mixtures are heated up to 1600 °C for a targeted reduction of predominantly transition metal oxides and a separation into a mineral fraction. Subsequently, controlled cooling of the molten material is implemented through water granulation. The produced granulate is crushed and sieved, and finally, the metallic and mineral fractions are magnetically separated. The chemical modification, reduction, and phase modification are tested to prevent landfilling and provide alternative secondary resources for the steel and cement industry. According to the results, it is possible to recover metals from metallurgical residues and simultaneously separate the modified mineral fraction as an alternative cement constituent. These findings will be further investigated through additional research to identify the variables that influence and impact/affect the reduction efficiency.

The 1.9 billion metric tons of steel globally manufactured in 2023 justify the steel industry’s pivotal role in modern society’s growth. Considering the rapid development of countries that have not fully taken part in the global market, such as Africa, steel production is expected to increase in the next decade. However, the environmental burden associated with steel manufacturing must be mitigated to achieve sustainable production, which would align with the European Green Deal pathway. Such a burden is associated both with the GHG emissions and with the solid residues arising from steel manufacturing, considering both the integrated and electrical routes. The valorisation of the main steel residues from the electrical steelmaking is the central theme of this work, referring to the steel electric manufacturing in the Dalmine case study. The investigation was carried out from two different points of view, comprising the action of a plasma electric reactor and a RecoDust unit to optimize the recovery of iron and zinc, respectively, being the two main technologies envisioned in the EU-funded research project ReMFra. This work focuses on those preliminary steps required to detect the optimal recipes to consider for such industrial units, such as thermodynamic modelling, testing the mechanical properties of the briquettes produced, and the smelting trials carried out at pilot scale. However, tests for the usability of the dusty feedstock for RecoDust are carried out, and, with the results, some recommendations for pretreatment can be made. The outcomes show the high potential of these streams for metal and mineral recovery.

Mineral wool products are man-made vitreous fibres (MMVFs), such as glass wool and stone wool, mainly used for thermal and acoustic insulation. Demolition of buildings generates mineral wool (MW) waste. With regard to the intended recycling of materials, the European Union's circular economy package currently foresees a landfill ban for certain waste streams by 2030. As a result, Austria will have a landfill ban for MMVFs from 2027. This paper presents an investigated route for the recycling of MW waste into new mineral wool (wool2wool). The recycling route aims to conserve valuable and limited landfill volume and enables the reduction of primary resource consumption and CO2 emissions. The investigation was based on pH-dependent leaching tests of the fibres according to ÖNORM EN 14429 and hydrogeochemical modelling using LeachXS/Orchestra to identify the solubility-controlling mechanisms. The next step was a thermochemical treatment using correction materials to adjust the chemical composition, followed by rapid cooling through a spinning process. Another focus was on the theoretical determination of the dynamic viscosity to ensure suitable flow behaviour during fibre production. The chemical composition of the mineral wool produced was analysed, and it was shown that the target formulation could not be achieved for all elements within the permitted variation. The variations were due to the dissolution of the kiln lining, which had a more significant influence on the experiment than expected. Overall, the recycling pathway showed a high potential for CO2 savings, resource savings and other environmental benefits by recycling waste that is currently landfilled.

Zusammenfassung: Die Hochtemperaturprozesstechnik als Arbeitsgruppe des Lehrstuhls für Thermoprozesstechnik beschäftigt sich mit konkreten metallurgischen und verfahrenstechnischen Problemstellungen bei Temperaturen über 1000 °C. Die gegenwärtig behandelten Schwerpunkte der Arbeitsgruppe sind Recycling- bzw. Wärmerückgewinnungsprozesse sowie Brenner- und Industrieofentechnik. Die grundlegende Motivation liegt dabei in der nachhaltigen Primärressourcenschonung, Abfallvermeidung sowie der Energieeffizienzsteigerung von Gesamtprozessen.In Folge werden die Bestrebungen anhand der Kompetenzen und Anlagenausstattung sowie der aktuellen Forschungsprojekte am Lehrstuhl im Bereich der Hochtemperaturprozesstechnik dargelegt.