How Does the Sponge Iron Production Process Work in Modern Metallurgy?

Tid: 7 October 2025

The sponge iron production process is a modern method widely used in metallurgy to produce iron in a physical and chemically reduced state without melting, primarily for use in steelmaking. Sponge iron, also known as direct reduced iron (DRI), is a porous, solid iron product obtained by reducing iron ore using various reducing agents. Here’s how the process works:

1. Raw Material Used

• Iron Ore: Typically, hematite (Fe₂O₃) or magnetite (Fe₃O₄) is used as the primary source of iron.
• Reducing Agent: Usually non-coking coal or natural gas is used as the reducing agent to remove oxygen from iron ore.
• Other Additives: Limestone or dolomite may be added to remove impurities.

2. Reduction Process:

Sponge iron is produced through direct reduction, meaning iron ore is reduced to metallic iron at temperatures below its melting point (800–1200°C). There are two widely used methods:

A. Coal-Based Process:

• Iron ore is crushed and mixed with non-coking coal as the reducing agent.
• The mixture is then heated in rotary kilns or vertical shaft furnaces at around 900–1000°C.
• Oxygen molecules in iron ore react with carbon from coal to form carbon monoxide and carbon dioxide, leaving behind solid metallic iron (sponge iron).

• Key reaction:
  Fe₂O₃ + CO → Fe + CO₂
  Fe₂O₃ + C → Fe + CO + CO₂

  B. Gas-Based Process:

• Iron ore is reduced using natural gas as the reducing agent (predominantly methane, CH₄).
• Natural gas is first reformed into a mixture of hydrogen (H₂) and carbon monoxide (CO).
• Reduction takes place in reactors such as shaft furnaces at temperatures of 800–1000°C.
• Key reaction:
  Fe₂O₃ + H₂ → Fe + H₂O
  Fe₂O₃ + CO → Fe + CO₂

3. Cooling and Separation:

• After the reduction process, the sponge iron is cooled to prevent oxidation.
• Excess reducing agent or impurities are removed mechanically.

4. Advantages of Sponge Iron Production:

• Energieffektivitet: Requires less energy than the blast furnace process.
• Flexibility: Can use coal or gas as reducing agent, making it adaptable to local resources.
• Environmentally Friendly: Produces fewer emissions compared to traditional methods.
• High Yield: Produces high-purity iron suitable for steelmaking.

5. Applications of Sponge Iron:

• Sponge iron is mainly used as a feedstock in Electric Arc Furnaces (EAFs) and induction furnaces to produce high-quality steel.
• Can also be used directly in steelmaking as a substitute for scrap steel.

Summary:

The sponge iron production process is a highly efficient and environmentally friendly method of producing metallic iron without melting. By using reducing agents such as coal or natural gas, oxygen is removed from iron ore to produce porous iron suitable for further steelmaking applications. This process provides a sustainable solution, particularly for countries lacking coking coal reserves.

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