Iron ore raw materials

Man began to make and use iron tools during the Iron Age, about four thousand years ago. Today, iron ores are one of the most common minerals. Perhaps, only coal and construction materials are mined on a larger scale. More than 90 % iron ores are used in metal sector for producing pig iron and steel.

Pig iron is a usually brittle iron-carbon alloy with 2–4 % carbon that also contains residual elements like silicon, manganese, sulphur, phosphorus and sometimes alloying elements like chromium, nickel, vanadium, aluminium, etc. Pig iron is produced from iron ores in blast furnaces. A major portion (over 85 %) of pig iron is processed into steel in the form of conversion pig iron and a minor portion is used as foundry pig iron to produce shaped castings.

Steel is a malleable alloy of iron, carbon (and alloying elements) and also the main end product of iron ore treatment. Steel has a high strength, toughness, ability to easily change form during hot and cold working and, depending on chemical composition and heat treatment method, acquire specific properties: high-temperature strength, abrasion resistance and corrosion resistance. That is why steel is a construction material of paramount importance.

Iron and steel products are used in all areas of industrial production, mainly in engineering and capital projects.

Iron ore is a raw material for melting ferrous metals. Mined iron ore is commonly referred to as crudes.

Iron-ore raw materials are a type of iron source used in the metal sector for producing pig iron and metallized products (DRI and HBI) and also in small quantities for steelmaking. Iron ore raw materials are divided into two kinds: ready-made (agglomerated) and natural (unagglomerated) raw materials. Iron-ore raw materials of the first kind are ready to be used in blast furnaces to produce pig iron, while materials of the second kind are used to produce agglomerated raw materials. Natural raw materials include concentrates, direct-shipping ores and sinter ores. Concentrate is mainly produced by magnetic separation of fine low-grade ore. Iron recovery in concentrates is on average about 80 %, iron content in them being 60–65 %.

Sinter ore (iron-ore fines) is produced by crushing, screening and deslurrying high-grade ore rich in iron, fineness being less than 10 mm.

Direct-shipping ore (lumpy ore) is also produced from high-grade ore, fineness being minus 70 and plus 10 mm. Iron-ore raw materials for a blast-furnace process are usually sintered or pelletized. Sinter is made of sinter ore and concentrate while pellets are made of concentrates only.

Pellets are produced from iron-ore concentrate containing limestone by pelletizing the mixture into 1 cm pellets and their heat hardening.

Hot-briquetted iron iron is not an iron-ore raw material in the proper sense of the term, since it is a product of metallurgical extraction, actually. To produce sinter, a mixture of sinter ore, siderite, limestone and iron-bearing waste products rich in iron (like scale, etc.) is used as a raw material. The mixture is also pelletized and sintered.

In the metal sector, value of iron ores and concentrates is determined by their grade (iron percentage) as well as content of useful elements (Mn, Ni, Cr, V, Ti), harmful impurities (S, P, As, Zn, Pb, Cu, K, Na) and fluxing components (Si, Ca, Mg and Al oxides). The useful impurities are natural alloying elements in steel that improve its properties. The harmful impurities either impair metal properties (sulphur and copper result in red-short, phosphorus is the cause of cold brittleness, arsenic and copper decrease welding characteristics) or complicate operational process in a blast furnace (zinc damages blast-furnace brickwork, lead erodes the hearth, potassium and sodium facilitate incrustation in the flue system).

Sulphur should not exceed 0.15 % in commercial ore. Acceptable sulphur content in ores and concentrates for producing sinter and pellets is 0.6 % max, as sintering and heat hardening of pellets remove sulphur by 60- 90 %. Phosphorus content in ores, sinter and pellets is limited to 0.07–0.15 %. 0.05–0.1 % As max, 0.1-0.2 % Zn max and up to 0.2 % Cu are allowed in the iron-ore part of the blast-furnace burden for the production of standard conversion pig iron. Slag-forming components are divided into basic oxides (Ca, Mg) and acidic oxides (Si, Al). Ores and concentrates with a higher ratio of basic to acidic oxides are preferred, as in this case, consumption of raw fluxing materials during the subsequent metallurgical extraction reduces.

Iron ores — are natural mineral formations containing iron and its compounds in concentrations suitable for industrial extraction of iron. Although iron is present in a greater or lesser degree in all the rocks, iron ores are only understood as splashes of ferrous compounds from which metallic iron can be economically extracted on a massive scale.

Industrial types of iron ores are classified as follows:

• titanomagnetite and ilmenite- titanomagnetite in basites and ultrabasites;
• apatite-magnetite in carbonatites;
• magnetite and magnomagnetite in skarns;
• magnetite-hematite in banded iron formations;
• martite and martite-hydrohematite (rich ores formed in banded iron formations);
• goethite-hydrogoethite in crusts of weathering.

There are three types of iron ore products used in iron and steel industry: separated iron ore (ore in bulk concentrated by magnetic separation), sinter (sintered lumps produced after thermal treatment) and pellets (raw iron-bearing bulk usually fluxed with limestone and formed into pellets ca. 1–2 cm in diameter).

Composition

Chemically, iron ores are oxides, hydroxides and ferrous carbonates; they occur naturally as a variety of metallic minerals, of which the most important are magnetite, or lodestone; goethite, or specularite (red iron ore); limonite, or ironstone, including bog iron ores and marsh ores; and finally siderite, or spathic iron ore (chalybite) and its variety sphaerosiderite. Any splash of the above mentioned ore minerals is usually a mixture, albeit an intimate one at times, of them with iron-free minerals such as clay, limestone or even components of crystalline extrusive rocks. Sometimes, some of these minerals occur together in the same deposit, although in most cases some one mineral dominates and the others are allied.

Rich iron ore

Rich iron ore contains more than 57 % iron, less than 8–10 % silica, less than 0.15 % sulphur and phosphorus. It is a product of natural enrichment of banded iron formations originated by leaching quartz and decomposition of silicates during long-term weathering or metamorphosis. Lean iron ores may contain 26 % iron min.

Flat-like and linear ore bodies represent the two main morphological types of rich iron ore deposits. The flat-like ones underlay atop steeply sloping seams of banded iron formations in the form of expanded ore bodies with a pocket-like base and are classified as typical crusts of weathering. The linear deposits represent dipping wedge-shape bodies of rich ores in zones of metamorphosis faults, jointing, crush and folds. The ores are characterized by high iron content 54–69 % and low sulphur and phosphorus. Pervomayskoye and Zheltye Vody deposits in the northern part of Krivoy Rog Basin are perfect examples of the metamorphosis deposits of rich ores. The rich iron ores are used for steelmaking in open-hearth furnaces and converters or for producing direct-reduced (hot-briquetted) iron.

Reserves

By estimate, world proven reserves of iron ore are about 160 billion tons and contain about 80 billion tons of metallic iron. According to the U.S. Geological Survey, the share of iron ore deposits in Russia and Brazil accounts for 18 % of the world reserves of iron. World resources and reserves of iron ore as of January 1, 2010 are as follows:

The largest producers of iron ore in 2010

According to the US Geological Survey, world production of iron ore totaled 2.3 billion tons in 2009 (an increase by 3.6 % as compared to 2008).

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