In the world of modern steelmaking, the materials used as feedstock play a critical role in determining the quality, cost-efficiency, and environmental impact of the final product. This article explore sponge iron meaning, how it’s made, where it’s used, properties, compostions, prices, and how it compares to pig iron. Whether you’re a manufacturer, engineer, or student, understanding the role of sponge iron is crucial to grasping the future of sustainable steelmaking.
What is Sponge Iron?
Sponge iron, also known as direct reduced iron (DRI), is a form of iron produced by reducing iron ore (usually in the form of pellets or lumps) using a reducing gas or elemental carbon, typically without melting the ore. The process removes oxygen from the iron ore, leaving behind a porous, sponge-like structure of metallic iron. This material is widely used as a raw material in steelmaking, especially in electric arc furnaces, because it is relatively pure and consistent in quality. Sponge iron is valued for its efficiency, lower emissions compared to traditional blast furnace methods, and ability to recycle iron-containing waste materials.
Why DRI is Called Sponge Iron?
DRI (Direct Reduced Iron) is called sponge iron because of its porous, sponge-like appearance that results from the removal of oxygen from iron ore during the reduction process. When iron ore is reduced in a solid-state using gases like hydrogen or carbon monoxide (derived from natural gas or coal), the resulting metallic iron retains a microscopic honeycomb structure. This texture resembles a sponge, giving it the name “sponge iron.” The spongy texture also makes it more reactive and easier to melt in electric furnaces, which is ideal for steelmaking.
What is Sponge Iron Used For?
Sponge iron, or Direct Reduced Iron (DRI), is widely used in the steelmaking industry due to its consistent quality, high iron content, and clean composition. Here are its primary applications:
1. Steel Manufacturing via Electric Arc Furnace (EAF) & Induction Furnace (IF)
Sponge iron is primarily used as a substitute or supplement for steel scrap in EAF and IF steelmaking processes. It provides a cleaner and more uniform charge material, especially where scrap quality is low or inconsistent.
2. Production of High-Quality Steel
Factories use sponge iron to produce specialty steels (e.g., stainless, alloy, or tool steels). Why?: Sponge iron allows precise control of chemistry due to its low impurity levels compared to mixed steel scrap.
3. Scrap Supplement or Replacement
When scrap is expensive or scarce, sponge iron becomes a cost-effective, reliable feedstock. It reduces dependence on scrap imports and helps maintain consistent furnace operation.
4. Blending with Other Iron Sources
Sponge iron is often mixed with hot metal or pig iron in integrated steel plants to improve the efficiency and control of steelmaking processes.
5. Environmentally Friendly Steel Production
Sponge iron contributes to lower emissions and energy efficiency compared to traditional blast furnace methods. It’s used by eco-conscious manufacturers looking to reduce their carbon footprint.
6. Rebar and Construction Steel Production
Used in manufacturing TMT bars, rods, structural beams, and angles for the construction industry. Offers better quality control and strength consistency compared to some scrap-based products.
Sponge Iron Compositions
Sponge iron, also known as Direct Reduced Iron (DRI), typically contains 84% to 95% elemental iron (Fe), depending on the quality of the raw material and the reduction process used. Below is a general breakdown of its composition:
| Component | Typical Range |
| Total Iron (Fe) | 84% – 95% |
| Metallic Iron (Feₘ) | 80% – 92% |
| Carbon (C) | 0.1% – 0.4% |
| Sulfur (S) | ≤ 0.02% |
| Phosphorus (P) | ≤ 0.06% |
| Gangue (SiO₂, Al₂O₃) | 2% – 6% |
| Moisture | ≤ 1% |
The high iron content and low impurities make sponge iron an excellent feedstock for steel production in Electric Arc Furnaces (EAF) and Induction Furnaces (IF). The porous structure helps in better melting efficiency. Sponge iron is more environmentally friendly than traditional pig iron due to its cleaner production process.
What is Sponge Iron Price?
Hot‑briquetted iron (HBI / densified sponge iron), CFR Asia:
Price assessed at US $330–338 per tonne (as of May 23)
Indian DRI export (FOB India):
Price trends have declined over recent months, standing around US $299 per tonne in March 2025
Sponge Iron Manufacturing Process
The sponge iron manufacturing process—also called the Direct Reduction Iron (DRI) process—involves converting iron ore into metallic iron without melting it. Here’s a step-by-step explanation:
1. Raw Materials Feeding
Iron Ore (usually in the form of lumps or pellets) and Non-Coking Coal are the primary raw materials. Both are fed into a rotary kiln, which is a long, inclined cylindrical furnace that rotates slowly.
2. Reduction Reaction in Rotary Kiln
The kiln is heated to 800–1,200°C. Coal acts as a reducing agent, providing carbon monoxide (CO) and hydrogen (H₂). These gases reduce the iron oxide in ore (Fe₂O₃ or Fe₃O₄) into solid metallic iron (Fe) without melting it.
3. Formation of Sponge Iron
The end product is porous, metallic iron that looks like a sponge—hence the name. It retains some non-metallic impurities and unburnt carbon.
4. Cooling & Magnetic Separation
The hot sponge iron is discharged into a cooling chamber or rotary cooler. It’s cooled with water and air, then passed through magnetic separators to separate sponge iron from char (residual coal).
5. Final Product
The sponge iron (usually 90–94% metallic iron) is collected and can be used in electric arc furnaces for steelmaking. Briquetted into HBI (Hot Briquetted Iron) for easier handling and transport.
Sponge Iron Properties
Compared to solid steel or pig iron, sponge iron is mechanically weaker and more prone to breakage during handling. Can be compacted into briquettes (HBI) for transport or storage. Due to its high porosity and reactivity, sponge iron is prone to oxidation and spontaneous combustion, especially when moist. This is why it’s either used quickly in furnaces or compacted into hot briquetted iron (HBI) for safe storage.
| Property | Description |
| Form | Porous, solid material with a sponge-like structure |
| Color | Dull grey or metallic |
| Density | ~2.5 to 3.5 g/cm³ (lower than solid iron due to porosity) |
| Porosity | High internal porosity allows for better reactivity and melting efficiency in furnaces |
| Metallic Iron (Fe) | Typically 80% to 94% Fe (high metallization) |
| Carbon Content | Low, usually around 0.1% to 0.2% |
| Impurities | Contains small amounts of silica (SiO₂), alumina (Al₂O₃), sulfur (S), phosphorus (P), and gangue material |
| Reactivity | Highly reactive, especially with moisture and oxygen (must be stored carefully to avoid re-oxidation or spontaneous heating) |
| Melting Point | Around 1,538°C, but begins softening earlier due to porosity and residual impurities |
| Shape & Size | Comes as lumps or pellets, often irregular in shape |
| Thermal Conductivity | Lower than solid iron due to porosity, but sufficient for use in EAFs and IFs |
Sponge Iron vs Pig Iron, What’s the Difference?
| Aspect | Sponge Iron (DRI) | Pig Iron |
| Definition | Direct reduced iron (DRI), made by reducing iron ore without melting | Intermediate product obtained from smelting iron ore in a blast furnace |
| Production Process | Produced via direct reduction (using gas or coal in rotary kilns or shaft furnaces) | Produced in a blast furnace with coke, limestone, and iron ore |
| Form | Porous, sponge-like structure in solid form | Liquid metal solidified into ingots or pigs |
| Carbon Content | Low (0.1%–0.2%) | High (3.5%–4.5%) |
| Other Elements | Low sulfur and phosphorus, minimal slag content | High amounts of carbon, silicon, sulfur, and phosphorus |
| Physical Strength | Brittle and fragile, must be handled with care | Stronger and denser |
| Reactivity | Highly reactive, especially with moisture and air (prone to oxidation) | Less reactive than sponge iron |
| Main Use | Used as a steelmaking feedstock in Electric Arc Furnaces (EAF) or Induction Furnaces (IF) | Used for making cast iron, or further refined to steel |
| Melting Point | Slightly higher (~1538°C), due to low carbon content | Lower due to high carbon content (~1150–1200°C) |
| Environmental Impact | More eco-friendly (lower emissions, uses less coke/coal) | Higher emissions due to coke combustion in blast furnace |
Which Should You Choose, Pig Sponge vs Pig Iron?
Choose Sponge Iron if:
-You’re using an electric arc or induction furnace
-You want a cleaner, low-carbon steel feedstock
-You’re aiming for environmentally friendly steelmaking
Choose Pig Iron if:
-You’re making cast iron products
-You require a cheaper, high-carbon feedstock for basic steelmaking
-You’re using traditional blast furnace and converter setups