Mining for Iron and Steel

Iron and Steel and manufactured using the two main raw materials: iron ore and metallurgical coal. These are mined, processed and the converted to iron and steel through different process routes like blast furnace, direct reduced iron, basic oxygen furnace and electric arc furnace.

Raw Materials

Iron ore

The USGS defines iron ore as a mineral substance which, when heated in the presence of a reductant, will yield metallic iron (Fe). It almost always consists of iron oxides, the primary forms of which are magnetite (Fe₃O₄) and hematite (Fe₂O₃). Iron-ore is generally classified into three based on its quality as:

• High-grade ore with more 60% Fe content, like the Brazilian and Australian hematite
• Medium grade ore with 55-60% Fe content
• Low-grade ore with less than 55% Fe content

Iron ore is the major raw material in steelmaking. Iron ore is the world’s third most produced commodity by volume - after crude oil and coal - and the second most traded commodity after crude oil. Globally, over 2,000 million tons of iron ore is mined in a year. Almost all of the iron ore (95-98%) is used in steelmaking.

Metallurgical Coal

Coal is considered one of the world’s most affordable energy fuel and biggest source of fuel for electricity generation. The history of coal mining and excavation often dates back to the industrial revolution. It has since been extensively used in production of iron, steel, cement, and fertilizers, generation of electricity and in steamships and trains. Coal is generally classified as coking coal and non-coking coal, due to differences in their chemical and physical properties. Coking coal has higher carbon content and lower ash content in comparison to non-coking coal. Coking coal is used for the production of coke, while non-coking coal is used for purposes like power generation. Over 70% of the global steel produced from iron ore is largely dependent on coal.

Stages of mining

Exploration

Mining begins with geological exploration to investigate the quality and quantity of deposits available. Core drilling is employed to study the potential of mine sites. The exploration of the mining site helps develop strategies for optimum exploration of the minerals.

Extraction

Most iron ore mining involves the use of the ‘open pit’ method, where the rock are drilled into and blasted with explosives to break the ore-bearing material loose. Huge excavators are then employed to gather the loosened ore. To mine metallurgical coal, vertical mine shafts are sunk into the deposits to access coal which is deposited in layers or ‘seams’ underground.

Transportation

The excavators then load the mined materials onto huge haul trucks or conveyors that carry the materials to processing plants. Sometimes trains and long-haul ships are also employed to transport raw materials from the mines to the processing sites.

Processing

In this stage, the raw materials are first stacked according to their grade. The minerals are then transformed into usable raw material. The iron ore is crushed and concentrated it in different ways, for example by milling, flotation or magnetic separation. The ore is processed further and sintered or pelletised for use in steelmaking.

Environmental Impacts

Mining of iron ore is a highly energy intensive process and causes air pollution in the form of nitrous oxide, carbon dioxide, carbon monoxide, and sulfur dioxide from diesel generators, trucks and other equipment. It also causes water pollution due to heavy metals and acid that drains to water sources from the mines. Acid drainage once caused can remain for thousands of years even after the mining activities have been stopped.