From ore to green steel with an approach to optimizing energy and carbon
This article is based on specialized analyzes by Dr. Babak Al-Tah, senior advisor in the field of geology and geometallurgy, and examines the role of geometallurgy in optimizing energy consumption, reducing carbon footprint, and facilitating the transition of the steel industry to low-carbon production.
Abstract
The steel industry is one of the largest consumers of energy and a major source of carbon dioxide emissions worldwide. In the transition to green steel, technologies such as hydrogen-based direct reduction, the use of renewable energies, the increase in the share of electric arc furnaces, and scrap recycling play a crucial role. However, one of the less visible issues in this path is the role of geological, mineralogical, and geometallurgical characteristics of iron ore in determining the energy intensity and carbon footprint of the steel production chain.
Geometallurgy, by linking geological, mineralogical, geochemical, mechanical, and process data, provides the possibility of predicting the behavior of ore in different stages of the steel value chain. This approach can help optimize energy consumption and reduce carbon emissions from the extraction and crushing stage to processing, concentrate production, pelletizing, direct reduction, and steelmaking.
In the context of low-carbon steel, geometallurgy is not just a processing tool or mine planning program, but rather a technical infrastructure for energy-oriented and carbon-oriented decision-making throughout the mine-to-steel chain.
1. Introduction
The steel industry is one of the main pillars of industrial development worldwide, with over two billion tons of steel produced annually. However, this industry is one of the most energy-intensive industrial sectors, accounting for approximately 7 to 9 percent of global carbon dioxide emissions.
The steel production chain begins with ore extraction and includes various stages, including mining, crushing and grinding, processing and concentration, pelletizing, direct reduction, sponge iron production, steelmaking, casting, and production of steel products. The performance of each of these stages is directly influenced by the geological, mineralogical, textural, physical, and mechanical characteristics of the initial ore.
In recent years, the focus of the steel industry has shifted towards technologies such as hydrogen-based direct reduction, renewable energies, and electric arc furnaces. Despite the importance of these technologies, the quality of the mineral material and the geometallurgical behavior of the feed remain one of the key factors in the success or failure of green steel projects.
2. Geometallurgy and the Challenge of the Green Steel Industry
The Transition of the Steel Industry to a Low-Carbon Economy
Climatic pressures, carbon taxes, ESG requirements, the Paris Agreement, and Net-Zero targets have forced the steel industry to move towards reducing energy intensity and carbon emissions.
In this path, green steel refers to steel whose production process has minimized carbon emissions as much as possible. However, producing green steel is not just about changing fuel or using renewable energy. To achieve low-carbon steel, the entire chain from mine to steel needs to be redesigned and optimized.
One of the most important links in this redesign is the accurate understanding of the behavior of the ore; this is where geometallurgy comes in.
Limitations of Traditional Approaches in Iron Ore Feed Management
In many mining and steel units, decision-making about extraction and feeding is mainly based on parameters such as iron grade, silica content, alumina, phosphorus, sulfur, and metal recovery.
Although these indicators are essential for controlling product quality, they are not sufficient to predict the actual behavior of the ore in downstream processes.
For example, two mineral blocks may have similar iron grades but exhibit completely different behavior in crushing, pelletizing, and direct reduction due to differences in iron ore mineral types, mineral liberation, hardness, mechanical resistance, texture, porosity, gangue mineral types and amounts, reducibility, and other factors.
Therefore, focusing solely on iron grade cannot be a suitable strategy for producing low-carbon steel.
Geometallurgy; The Link Between Geology and Steelmaking
Geometallurgy is an interdisciplinary approach that combines geological, mineralogical, geochemical, mechanical, and process data into an integrated model.
The main goal of geometallurgy is to predict the behavior of the ore throughout the production chain. In the iron ore industry, this approach can answer key questions such as:
- Which part of the deposit requires the least energy for crushing?
- Which mineral domain produces the best quality concentrate?
- Which type of iron ore is the most suitable feed for pelletizing?
- Which domain has the highest reducibility?
- Which part of the deposit creates the lowest carbon footprint in steel production?
Thus, geometallurgy establishes a direct connection between the geological characteristics of the deposit and the performance indicators of the steel chain.
3. The Role of Iron Ore Mineralogy in Pelletizing and Direct Reduction
In the steel production chain based on direct reduction, the quality of the feed is not just a function of the iron grade. The mineralogical composition, textural characteristics, and relationships between minerals play a determining role in the performance of concentration, pelletizing, and direct reduction processes.
From a geometallurgical perspective, each type of iron ore mineral exhibits different behavior in the stages of grinding, pellet formation, firing, reduction, and metallization.
Magnetite
Magnetite is one of the most desirable iron ore minerals for pellet production. The most important feature of magnetite is its oxidizability in the pellet firing process. This exothermic reaction provides part of the energy required for the firing process.
The advantages of magnetite in pelletizing include:
- Reduced fuel consumption in the firing kiln
- Increased strength of the fired pellet
- Improved hematitic bonds
- Reduced energy costs
However, magnetite usually requires finer grinding to achieve suitable liberation, which can reduce part of its energy advantage in upstream stages.
Hematite
Hematite lacks the potential for exothermic oxidation in the firing kiln. Therefore, the energy required for pelletizing must be largely supplied through external fuel.
The characteristics of hematitic pellets include:
- Higher energy requirement in firing
- Greater sensitivity to thermal cracks
- Higher fuel consumption in pelletizing
- Relatively good reducibility in direct reduction units
Therefore, hematite may be more energy-intensive from the perspective of pelletizing but can perform well in the reduction process.
Goethite, Limonite, and Martite
Goethite, due to its structural water, undergoes dehydration during heating. This process can increase the porosity of the pellet and improve the penetration of reducing gases, but on the other hand, it increases energy consumption in pelletizing.
Limonite also increases energy consumption in drying and firing due to its high inherent moisture and can reduce the strength of the pellet.
<p-Martite, which is the result of hematite replacing magnetite, usually has a porous structure and is considered one of the favorable iron ore phases for direct reduction, as it facilitates the penetration of reducing gases.The Role of Gangue Minerals
Gangue minerals also have a significant impact on pellet quality and reduction performance. Quartz, clay minerals, and carbonates are among the most important of these minerals.
Quartz can increase energy consumption in grinding, reduce iron grade, and increase slag volume. Clay minerals such as kaolinite, smectite, and illite can decrease the filtration efficiency of the concentrate by increasing its moisture content and thus increase the energy consumption of dryers.
Carbonates such as calcite and dolomite decompose during heating, consuming energy and directly emitting carbon dioxide.
4. Geometallurgical Models for Predicting Concentrate and Pellet Quality
One of the most important objectives of geometallurgy is to predict the behavior of the mineral feed before extraction and entry into the plant.
In traditional approaches, controlling the quality of the concentrate and pellet is mainly done through factory sampling and online process monitoring. However, in the geometallurgical approach, an attempt is made to predict the quality of the final products from the stage of deposit modeling.
The geometallurgical model is a set of quantitative relationships that relate geological and mineralogical variables to processing and metallurgical performance indicators:
Geological variables → Mineralogical variables → Geometallurgical variables → Process performance → Product quality
The input data for these models usually include:
- Geological data such as lithology, ore type, and geological structures
- Chemical data such as Fe, SiO₂, Al₂O₃, P, S, LOI, CaO, and MgO
- Mineralogical data such as the percentage of magnetite, hematite, goethite, martite, quartz, clay minerals, and carbonates
- Mechanical and process data such as Bond Work Index, fragmentation index, abrasion index, recovery, concentrate grade, pellet quality index, and reducibility index
In the new generation of geometallurgical models, indices such as Pellet Quality Index, Reducibility Index, Geometallurgical Energy Index, and Geometallurgical Carbon Index can be added to the block model of the deposit.
This allows each mineral block to be evaluated not only in terms of iron grade but also in terms of energy, carbon, reducibility, and pellet quality.
Conclusion
In the first part of the article, it was shown that geometallurgy can create a bridge between the geology of the deposit and the actual performance of the steel chain. The quality of the iron ore feed, the type of minerals, hardness, liberation degree, porosity, gangue minerals, and reducibility all affect energy consumption and carbon emissions.
Therefore, in the path to producing green steel, the best ore is not necessarily the one with the highest grade; rather, it is the ore that can be converted to steel with the lowest energy consumption, the lowest carbon footprint, and the highest process stability.