How lime enhances steel production
Steel is often seen as the foundation of modern civilization used in everything from skyscrapers and bridges to cars and renewable energy infrastructure. Yet behind the scenes, lime is a strategic asset in the steelmaking process. Its role goes far beyond chemistry as lime contributes to efficiency, quality, and environmental performance, making it indispensable in the steelmaking landscape.
Lime, primarily in the form of quicklime (CaO) and dolime (CaO·MgO), is a cost-efficient, and vital raw material in steelmaking. It plays a central role in the process by purifying and refining steel throughout key process stages. It is used predominantly as a fluxing agent during the ironmaking and steelmaking processes to promote slag formation which is essential to capture and remove impurities such as silica, phosphorus, and sulfur. Thereby lime improves steel quality, protects equipment, and enhances process efficiency.
In steel production, lime influences:
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Process Efficiency: Lime plays a dual role in steelmaking: enhancing both product quality and process efficiency. By accelerating the removal of impurities such as sulfur and phosphorus, lime helps in stabilizing furnace operations, reducing downtime, and lowering overall production costs. Its contribution to consistent slag formation also supports smoother workflows and better resource utilization.
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Material longevity: Dolime protects refractory linings and promotes slag foaming, extending the life of costly equipment.
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Environmental impact: Lime enables more sustainable production by reducing emissions of pollutants, improving waste management and supporting by-product recycling. It contributes to a more sustainable and responsible steelmaking process.
Key benefits of lime in steel production
Lime adds value at each stage of steel production from ironmaking to steelmaking:
At the beginning: Iron ore agglomeration and ironmaking
Before using iron ore in steelmaking, it must be transformed into larger, more uniform particles through a process called agglomeration. This includes techniques like sintering and pelletizing, which enhance the handling and performance of fine iron ores in both Direct Reduction (DR) plants and blast furnaces. Lime plays a crucial role in agglomeration improving the mechanical strength and reducibility of iron ore agglomerates. This leads to more consistent product quality, better furnace permeability and ultimately, increased productivity and efficiency in the steelmaking process.
During transformation: Crude steelmaking
Lime enables the efficient removal of impurities such as silica and phosphorus, which can compromise the strength, durability and overall quality of steel. In both basic oxygen furnaces (BOF) and electric arc furnaces (EAF), quicklime is used to form a basic slag that absorbs these impurities, while dolime helps extend the lifespan of refractory linings. When added to the process, dolime introduces MgO into the slag, which enhances buffering capacity. Excess MgO supports the protection of refractories and tap holes, reducing the need for gunning and frequent hot refractory repairs.
Our lime and dolime solutions do more than supporting steelmaking. By accelerating slag formation and enhancing its reactivity, our products significantly improve the impurity removal and protect the refractory linings ensuring more efficient furnace operations and better metallurgical outcomes.
In refining: Secondary metallurgy
Lime plays a key role in many secondary refining processes, where it performs critical functions, such as adjusting steel chemistry, removing residual impurities, and preventing the reabsorption of contaminants from slag back into the steel.
In the ladle furnace, our tailored lime and dolime blends are used to form synthetic slags, which act as a flux to remove additional sulfur and phosphorus after the initial steel refining process by forming calcium sulfate and calcium phosphate compounds that report to the slag.
Throughout the process, it protects furnaces and ladles, reducing downtime and extending the life of critical infrastructure. Each of these steps are essential to produce steel that meets today’s technical, economical, and environmental demands.
Supporting the transition to low-carbon steel
As the steel industry works to reduce its environmental footprint, the role of lime continues to evolve. It goes from improving process efficiency and quality, to enabling more sustainable production. To achieve these ambitious environmental objectives, we believe LEVEL|GREEN® lime will be a key enabler in transforming steel production toward a more sustainable future.
Once available, low-carbon lime and dolime, produced using, among other methods, renewable energy or carbon-capture technologies, offer a way to lower CO₂ emissions in steel production. By integrating low-carbon lime and dolime into existing and new processes, steel producers could take meaningful steps toward more sustainable steel. At Lhoist, we aim to support this through innovative solutions such as our LEVEL|GREEN® product range, designed to help industries meet their sustainability goals in a low-carbon future.
From agglomeration to secondary metallurgy, lime consistently enhances steelmaking processes. Its ability to improve impurity removal, protect infrastructure, and support cleaner production makes it an essential component in delivering high-quality steel.