Iron ore is the foundational raw material for nearly all steel production worldwide, with approximately 98% of mined iron ore dedicated to this purpose. This commodity is found primarily in the form of iron oxides like hematite and magnetite, which are extracted from the earth. Hematite ore typically contains up to 70% iron and is often directly shipped for use. Magnetite has a slightly higher theoretical iron content but often requires more extensive processing due to lower concentrations in the mined rock. The material is mined due to the global demand for steel in construction, automotive manufacturing, and infrastructure.
Locating and Extracting the Ore
The process of securing iron ore begins with extensive geological exploration and surveying to identify economically viable deposits. Geologists utilize advanced techniques such as remote sensing, magnetic surveys, and satellite imagery to pinpoint locations where the ore is concentrated. Once a promising site is confirmed, detailed planning determines the optimal extraction method based on the deposit’s depth, size, and the quality of the ore.
The most common method for iron ore recovery is open-pit mining, which is used when the ore body is near the surface. This technique involves removing the overlying soil and waste rock, known as overburden, to expose the ore deposit. The extraction proceeds in a series of steps called benches, which allow access to progressively deeper ore as the upper levels are removed.
To break the hard ore body into manageable pieces, miners employ a systematic process of drilling and blasting. Holes are drilled into the rock in a specific pattern, loaded with explosive mixtures, and detonated to fracture the material. Following the blast, massive equipment, including large electrical shovels, hydraulic excavators, and front-end loaders, move in to gather the fragmented ore.
The broken ore is then loaded onto large off-road dump trucks for transportation to the processing facility. Underground mining, which involves sinking shafts and creating tunnels to reach deep ore veins, is sometimes used for deposits that are too far beneath the surface for open-pit operations. However, surface mining is the preferred and predominant method worldwide due to its efficiency and lower cost for the large-scale operations required for iron ore.
Concentrating the Ore
Once the raw, fragmented ore arrives at the processing facility, the concentration phase, or beneficiation, begins to increase the iron content and remove impurities. The first step is primary crushing, where large chunks of ore are broken down into smaller fragments using machines like jaw crushers. This size reduction continues through secondary and tertiary crushing stages, followed by grinding, which reduces the ore to a fine powder to liberate the iron minerals from the waste materials, called gangue.
The separation technique used depends heavily on the type of iron oxide present in the ore. For magnetite, which is strongly magnetic, the process relies on magnetic separation. Under a magnetic field, the iron-rich particles are attracted and separated from the non-magnetic gangue minerals, such as quartz, with high efficiency. This method is highly effective for magnetite, often yielding a high-grade concentrate with low impurities.
For non-magnetic ores like hematite, a different approach is necessary, typically involving flotation or gravity separation. Flotation involves grinding the ore to a very fine state and mixing it with water and specific chemical reagents. These reagents cause the iron minerals to attach to air bubbles and float to the surface as a froth, or, more commonly in reverse flotation, they make the silica-based impurities hydrophobic so they float away, leaving a purified iron ore concentrate at the bottom. This separation of impurities is essential before the concentrate can be used in the steel-making process.
Final Preparation for Use
The fine iron ore concentrate produced after beneficiation cannot be used directly in a blast furnace because its powdery nature would impede the flow of gas and material. To address this, the concentrate must undergo an agglomeration process to create a feed material with the necessary physical properties. The two main agglomeration techniques are pelletizing and sintering.
Pelletizing involves mixing the fine concentrate with a binding agent, such as bentonite or limestone, and water in a rotating drum or disc to form small, uniform spheres known as green pellets. These pellets are then hardened through a high-temperature heat treatment process called induration, which gives them the mechanical strength and durability required for shipping and furnace use.
Sintering takes fine ore and flux materials and fuses them together into larger, porous, irregular clumps through combustion on a moving grate. This thermal process binds the particles together into a suitable charge material for the blast furnace. The finished products, whether pellets or sinter, are then transported via various means, including rail and ship, to steel mills around the world. This final preparation step ensures that the iron feed material has the correct size and strength to maintain permeability and operate efficiently within the steel production furnaces.