Direct reduced iron

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Direct reduced iron (DRI), also called sponge iron, [1] is produced from the direct reduction of iron ore (in the form of lumps, pellets, or fines) into iron by a reducing gas or elemental carbon produced from natural gas or coal. Many ores are suitable for direct reduction.


Direct reduction refers to solid-state processes which reduce iron oxides to metallic iron at temperatures below the melting point of iron. Reduced iron derives its name from these processes, one example being heating iron ore in a furnace at a high temperature of 800 to 1,200 °C (1,470 to 2,190 °F) in the presence of the reducing gas syngas, a mixture of hydrogen and carbon monoxide. [2]


Direct reduction processes can be divided roughly into two categories: gas-based, and coal-based. In both cases, the objective of the process is to remove the oxygen contained in various forms of iron ore (sized ore, concentrates, pellets, mill scale, furnace dust, etc.), in order to convert the ore to metallic iron, without melting it (below 1,200 °C (2,190 °F)).

The direct reduction process is comparatively energy efficient. Steel made using DRI requires significantly less fuel, in that a traditional blast furnace is not needed. DRI is most commonly made into steel using electric arc furnaces to take advantage of the heat produced by the DRI product. [3]


Direct reduction processes were developed to overcome the difficulties of conventional blast furnaces. DRI plants need not be part of an integrated steel plant, as is characteristic of blast furnaces. The initial capital investment and operating costs of direct reduction plants are lower than integrated steel plants and are more suitable for developing countries where supplies of high grade coking coal are limited, but where steel scrap is generally available for recycling. India is the world’s largest producer of direct-reduced iron. [4] Many other countries use variants of the process.

Factors that help make DRI economical:


Direct reduced iron is highly susceptible to oxidation and rusting if left unprotected, and is normally quickly processed further to steel.[ citation needed ] The bulk iron can also catch fire since it is pyrophoric. [6] Unlike blast furnace pig iron, which is almost pure metal, DRI contains some siliceous gangue (if made from scrap, not from new iron from direct reduced iron with natural gas), which needs to be removed in the steel-making process.


Producing sponge iron and then working it was the earliest method used to obtain iron in the Middle East, Egypt, and Europe, where it remained in use until at least the 16th century. There is some evidence that the bloomery method was also used in China, but China had developed blast furnaces to obtain pig iron by 500 BCE.

The advantage of the bloomery technique is that iron can be obtained at a lower furnace temperature, only about 1,100 °C or so. The disadvantage, relative to a blast furnace, is that only small quantities can be made at a time.


The following reactions successively convert hematite (from iron ore) into magnetite, magnetite into ferrous oxide, and ferrous oxide into iron by reduction with carbon monoxide or hydrogen. [7]

Carburizing produces cementite:


Sponge iron is not useful by itself, but can be processed to create wrought iron or steel. The sponge is removed from the furnace, called a bloomery, and repeatedly beaten with heavy hammers and folded over to remove the slag, oxidise any carbon or carbide, and weld the iron together. This treatment usually creates wrought iron with about three percent slag and a fraction of a percent of other impurities. Further treatment may add controlled amounts of carbon, allowing various kinds of heat treatment (e.g. "steeling").

Today, sponge iron is created by reducing iron ore without melting it. This makes for an energy-efficient feedstock for specialty steel manufacturers which used to rely upon scrap metal.

See also

Related Research Articles

Smelting Use of heat and a reducing agent to extract metal from ore

Smelting is a process of applying heat to ore in order to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a chemical reducing agent to decompose the ore, driving off other elements as gases or slag and leaving the metal base behind. The reducing agent is commonly a fossil fuel source of carbon, such as coke—or, in earlier times, charcoal. The oxygen in the ore binds to carbon at high temperatures due to the lower potential energy of the bonds in carbon dioxide. Smelting most prominently takes place in a blast furnace to produce pig iron, which is converted into steel.

Coke (fuel) A grey, hard and porous fuel with high carbon content and few impurities.

Coke is a grey, hard, and porous fuel with a high carbon content and few impurities, made by heating coal or oil in the absence of air—a destructive distillation process. It is an important industrial product, used mainly in iron ore smelting, but also as a fuel in stoves and forges when air pollution is a concern.

Iron ore Ore rich in iron or the element Fe

Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe
, 72.4% Fe), hematite (Fe
, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H2O), 55% Fe) or siderite (FeCO3, 48.2% Fe).

Steelmaking Process for producing steel from iron ore and scrap

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Syngas Fossil fuel derived from other hydrocarbon sources

Syngas, or synthetic gas, is a fuel gas mixture consisting primarily of hydrogen, carbon monoxide, and very often some carbon dioxide. The name comes from its use as intermediates in creating synthetic natural gas (SNG) and for producing ammonia or methanol. Syngas is usually a product of coal gasification and the main application is electricity generation. Syngas is combustible and can be used as a fuel of internal combustion engines. Historically, it has been used as a replacement for gasoline, when gasoline supply has been limited; for example, wood gas was used to power cars in Europe during WWII. However, it has less than half the energy density of natural gas.

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Industrial processes

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Iron(II,III) oxide Chemical compound

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Bloomery Type of furnace once used widely for smelting iron from its oxides

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