General Framework of the Iron-Steel and Metallurgy Sector

Türkiye is among the world's top ten crude steel producers, and the sector feeds dozens of sub-sectors, chiefly automotive, construction, white goods, machinery, defense, shipbuilding and energy.

Metallurgy is the engineering discipline that studies the extraction, refining, alloying and shaping of metals from ore; iron and steel constitutes the highest-volume branch of this discipline.

The production line starts from iron ore, coking coal, scrap metal and slag-forming additives, reaching crude steel via the blast furnace or electric arc furnace, and then the continuous casting and rolling mill lines. As of 2026, owing to its high carbon footprint, the sector is undergoing an intense transformation around topics such as green steel, hydrogen reduction, direct reduced iron (DRI) and carbon capture.

General Framework of the Iron-Steel and Metallurgy Sector

Iron-Steel Production Processes and Fundamental Steps

Modern iron and steel production is based on two main methods: integrated plants (BF-BOF, i.e. the blast furnace - basic oxygen furnace route) and electric arc furnace (EAF) plants.

In the integrated route, iron ore, coking coal and slag-forming materials are charged into the blast furnace; the liquid hot metal obtained here is subsequently converted into steel in the basic oxygen furnace by lowering its carbon through oxygen blowing.

In the EAF route, scrap metal or direct reduced iron (DRI) is melted with electrical energy. Both methods pass through similar stages: raw material preparation, preheating, melting, refining, casting, rolling and final heat treatment.

Iron-Steel Production Processes and Fundamental Steps

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Slag Chemistry and Impurity Control in Metallurgical Reactions

Slag is a critical by-product at the heart of iron and steel production that is often overlooked. Slag is the oxide melt floating on top of the liquid metal and performs three fundamental functions: isolating the liquid metal from the atmosphere, reducing heat losses and removing undesired elements from the metal.

For slag to be functional, its basicity (CaO/SiO₂ ratio) must be controlled. This ratio is generally kept between 2.5 and 4 depending on the production type.

Insufficient basicity causes sulfur and phosphorus to return from the slag back into the metal, while excessive basicity disrupts the viscosity of the slag and accelerates refractory wear. The fundamental components in slag chemistry are calcium oxide (CaO), magnesium oxide (MgO), silicon dioxide (SiO₂) and aluminum oxide (Al₂O₃).

Slag Chemistry and Impurity Control in Metallurgical Reactions

The Role of Lime-Based Solutions in Iron-Steel Production

In iron-steel and metallurgy processes, lime products are indispensable in terms of production efficiency and final steel quality. The most heavily used products in the sector are quicklime (CaO, calcium oxide), dolomitic quicklime (CaO·MgO), aggregate-grade limestone particles, and, in auxiliary processes, hydrated lime and gas-removing lime products.

The function of each is directed toward a different chemical objective at different stages. Quicklime (CaO): Used as a slag former in basic oxygen furnaces (BOF) and generally dosed at 30-50 kg per ton of steel.

When charged together with scrap in electric arc furnaces (EAF), the typical usage range is at the level of 30-90 kg per ton of steel. When added to the slag, it reacts with impurities such as silicon, phosphorus and sulfur, enabling their removal from the metal.

The Role of Lime-Based Solutions in Iron-Steel Production

Sulfur and Phosphorus Removal: The Critical Task of Quicklime

Sulfur is an undesired element because it causes hot shortness, forming problems and reduced corrosion resistance in steel. For this reason, lowering the sulfur level from the hot metal stage onward is one of the priorities of modern steel production.

The Hot Metal Desulfurization (HMD) process is carried out by injecting a fluidized mixture of ground lime or calcium carbide into the liquid hot metal via a lance. Inert gases such as argon or nitrogen serve as the carrier.

Since the reaction is diffusion-controlled, how fine and reactive the lime particle is directly determines the removal efficiency. Phosphorus removal, on the other hand, is performed at the BOF stage by correctly balancing the basicity and oxidation conditions.

Sulfur and Phosphorus Removal: The Critical Task of Quicklime

Sustainable Iron-Steel Production and Auxiliary Materials as of 2026

The steel sector is responsible for approximately seven percent of global CO₂ emissions, and as of 2026 the pressure for green transformation is higher than ever. The EU Carbon Border Adjustment Mechanism (CBAM) creates a direct financial impact on firms exporting steel from Türkiye to Europe.

Within this framework, auxiliary materials are also expected to have a low carbon footprint. High-activity lime with a homogeneous particle size provides a more efficient reaction with lower consumption in the steel plant, thereby indirectly offering an emission reduction per ton.

The valorization of slag is also an important item on the sustainability agenda. BOF slag can be used as a substitute for cement clinker, while granulated blast furnace slag (GBFS) has become one of the fundamental components of low-carbon cements.

Sustainable Iron-Steel Production and Auxiliary Materials as of 2026

Frequently Asked Questions

Quicklime (CaO) acts as a slag former. It chemically binds impurities present in the liquid metal, such as silicon, sulfur and phosphorus, and transfers them to the slag. At the same time, by raising the basicity of the slag, it ensures the liquid metal is protected from the atmosphere and reaches the desired chemical composition. It is not possible to produce modern steel without lime.

Consumption varies according to the production method. While 30-50 kg of quicklime per ton of steel is generally used in the basic oxygen furnace (BOF), this value is between 30-90 kg in electric arc furnaces (EAF). When hot metal desulfurization and ladle metallurgy processes are added, the total lime consumption can rise even further.

Slag basicity is expressed by the ratio of CaO to SiO₂ (CaO/SiO₂) in the slag and is typically kept between 2.5-4. If this ratio is too low, sulfur and phosphorus cannot pass from the metal to the slag; if it is too high, the slag loses its fluidity, reducing reaction efficiency and shortening refractory life.

The blast furnace (BF) produces liquid hot metal by reducing iron ore with coking coal; it is then converted into steel in the basic oxygen furnace. The electric arc furnace (EAF), on the other hand, melts scrap metal or direct reduced iron with electrical energy. The EAF route offers more flexible production and often lower direct CO₂ emissions.

In the hot metal desulfurization process, a mixture of finely ground lime or calcium carbide is injected into the liquid hot metal through a submerged lance together with an inert carrier gas such as argon or nitrogen. Since the reaction is diffusion-controlled, the finer and more reactive the lime is, the higher the removal efficiency.

While ordinary quicklime predominantly contains calcium oxide (CaO), dolomitic quicklime additionally contains a high proportion of magnesium oxide (MgO). MgO slows the wear of the refractory lining in steel plant furnaces. For this reason, the use of dolomitic lime extends furnace life and reduces maintenance costs.

Phosphorus causes cold shortness by reducing the toughness and formability of steel. At the BOF stage, high-basicity slag binds phosphorus as calcium phosphate (Ca₃(PO₄)₂) and removes it from the metal. The efficiency of this reaction depends largely on the quicklime dosage and slag composition.

Steel plant wastewater generally has a low pH, scale-derived suspended solids and heavy metals. By adding hydrated lime (Ca(OH)₂), the pH is raised to the 9-11 range; in this range, metals such as iron, zinc and chromium precipitate as hydroxides. At the same time, the hardness of the water is controlled and discharge limits are met.

Acidic components such as SO₂, HCl and HF present in sinter and EAF flue gases are captured by means of lime-based sorbents in dry sorbent injection (DSI) or semi-dry desulfurization (SDA) systems. As a result of the reaction, solid salts such as calcium sulfate and calcium chloride form and are retained in the filters.

Next-generation routes such as hydrogen reduction and direct reduced iron (DRI) do not eliminate the need for lime; on the contrary, they increase the demand for high-purity, high-activity lime. This is because controlling the steel chemistry, lowering sulfur and treating the flue gases are necessary in every scenario. Low-carbon lime production has become a critical supply criterion after 2026.