Iron ore is a rock or mineral deposit from which metallic iron can be extracted economically. This material is the fundamental raw material for the production of steel, which forms the backbone of global infrastructure and manufacturing. Iron does not naturally exist in a pure metallic state on Earth’s surface but is chemically bonded with other elements, most commonly oxygen.
The Primary Minerals and Ore Classifications
Iron ores are predominantly composed of iron oxides, and their commercial value depends on the iron concentration and mineral type. The two most significant iron minerals are hematite (Fe2O3) and magnetite (Fe3O4). Hematite is the most widely sought-after ore because its pure form contains approximately 70% iron by weight and often requires less intense processing before smelting.
Magnetite is another major ore, which, in its pure state, contains a slightly higher iron content of about 72.4%. Its strong magnetic property allows for efficient separation from waste rock using magnetic fields. Other less common but commercially relevant ores include goethite, a hydrated iron oxide, and limonite.
Ores are classified by quality. A notable low-grade ore is Taconite, a hard sedimentary rock containing fine-grained iron minerals, typically magnetite, interlayered with quartz. Taconite, as mined, may only contain 25% to 30% iron, requiring extensive processing to concentrate the iron content. High-grade ores that can be shipped directly to steel mills with minimal preparation are called Direct Shipping Ores (DSO), which are usually hematite-rich deposits.
How Iron Ores Formed and Where They Are Found
The vast majority of commercial iron ore deposits formed billions of years ago in geological features known as Banded Iron Formations (BIFs). These unique sedimentary rocks are characterized by distinct, alternating layers of iron-rich minerals, such as hematite and magnetite, and bands of silica-rich chert. Their formation began in the oceans between 3.8 and 1.8 billion years ago, during the Archean and Proterozoic eons.
At that time, the oceans contained large amounts of dissolved iron, but the atmosphere had very little free oxygen. Primitive photosynthetic organisms, such as cyanobacteria, began releasing oxygen into the seawater. This oxygen reacted chemically with the dissolved iron, causing it to precipitate out of the water as insoluble iron oxides that settled on the ocean floor.
The cyclical nature of this process led to the layering of iron-rich bands and silica-rich bands. These ancient BIFs are now found on nearly every continent and provide the source for most modern iron mining. Major deposits originating from BIFs are found in regions like the Hamersley Basin in Australia, the Carajás Mine in Brazil, and the Mesabi Range in the United States.
The Process of Extracting Iron from Ore (Smelting)
The transformation of iron ore into metallic iron involves a multi-stage industrial process that begins with mining and ends with chemical reduction in a furnace.
Mining and Beneficiation
Most iron ore is extracted from large, surface-level deposits using open-pit mining methods. Once mined, the raw ore undergoes beneficiation, a preparation step to increase the iron concentration and remove impurities, known as gangue.
Beneficiation starts by crushing large ore chunks and grinding them into a fine powder to separate the iron-bearing minerals from the surrounding rock. For magnetite ores, magnetic separation uses powerful magnets to pull the iron particles away from the non-magnetic gangue. Non-magnetic hematite ores are concentrated using gravity separation or flotation techniques.
Agglomeration
The resulting fine iron concentrate is too powdery to be efficiently used in a blast furnace, so it must be agglomerated through pelletizing or sintering. Pelletizing involves mixing the concentrate with a binder and rolling it into marble-sized spheres. These spheres are then hardened by firing at high temperatures, creating a uniform product that allows gases to flow through the furnace effectively.
Smelting in the Blast Furnace
The final step is smelting, which occurs in a large structure called a blast furnace. Iron ore (as pellets or sinter), coke (a form of carbon), and limestone (a flux) are continuously fed into the top of the furnace. A blast of hot air, reaching temperatures up to 2,000°C, is injected near the bottom.
The burning coke serves two purposes: it provides the intense heat necessary for the process and reacts with oxygen to form carbon monoxide (CO), which acts as the primary reducing agent. The carbon monoxide chemically strips the oxygen from the iron oxide minerals, reducing them to molten iron. The limestone reacts with the remaining impurities in the ore, such as silica, to form a molten waste product called slag. Slag floats on top of the heavier molten iron and is tapped off separately. The resulting product is pig iron, which is then further refined to make steel.