Iron ore

The iron ore is a Roche containing Fer, generally in the form of Oxyde S, like the Bauxite.

The iron ores have a content of variable iron according to iron-bearing mineral; also knowing that isomorphism, almost always present in natural minerals, reduced theoretical content.

The oxides which form the gangue obviously will decrease the content of Fer of the Minerai S employed.

Compared to their content of Iron, the Minerai S are classified in:

* raffs: Fe <= 30%

* average ores: Fe = 30% ÷ 50%

* high-grade ores: Fe > 50%

The content of iron of the mineral native lies between approximate limits:

* mineral magnetic: Fe = 50% ÷ 67%

* mineral of hematite: Fe = 30% ÷ 65%

* mineral of limonite: Fe = 25% ÷ 45%

* mineral carbonates: Fe = 30% ÷ 40%

Principal the Minerai S of iron is Sulfure S, Carbonate S and Oxyde S.

the Sulfure S, whose principal representatives are the Pyrite and the Pyrrhotite, are never used directly for the production of iron because of the weakening effect of the Soufre on the Alliage S ferrous. They constitute on the other hand an important primary matter for the production of Sulfur dioxide, obtained thanks to the Grillage. There remains a residue of Oxide iron (“pyrite ashes”) which is pulverulent and can still contain awkward quantities of Soufre: its use as Minerai of Fer can thus appear problematic.
Like Carbonate, one finds the Sidérite or siderite , FeCO₃, which gives the Oxyde by Calcination. With the humid air, the Sidérite is transformed into Lépidocrocite or, more rarely, into Goethite. The Sidérite is frequently associated with the Pyrite, the Magnésie, the Chaux, the Manganèse. One distinguishes the spathic spathic iron , ore crystalline white, slightly yellowish, very widespread, and the sphaerosiderite , in spheroid masses, mixed with settleable solids, rare in France. The ore of the layers of Houille contains coal: it is of black color and easy netting. In England it is known like blackband .

The Magnetite, ferrimagnetic spinel Fe₃O₄, is the iron mineral richest in metal. It is often associated with hematite in same the lodging, but pure magnetite lodgings are also known. Density 5,15, black color, metallic luster, often accompanied by impurities like the Silica, the Lime, the Alumina and the Phosphorus.

The Hematite α-Fe₂O₃, is component the most important of iron minerals treated in the Iron and steel industry. It east comprises several types:

* l'oligiste crystallizes in rhombohedrons and often replaces the Pyrite (Pseudomorphisme);

* the spécularite consists of aggregates of specular hematite flakes of appearance and silver plated color;

* l'hématite red ordinaire is presented in fibrous, earthy or compact masses;

* l'hématite red oolitique is formed small agglomerated spheres;

* the martite is a hematite which results from the oxidation of magnetite.

The Maghémite, γ-Fe2O₃, is a metastable form of the Hématite, α-Fe2O₃, which is formed starting from the Magnétite by progressive oxidation. It has the same magnetic characteristics of magnetite, whereas hematite is slightly magnetic. The structure is spinel, but with gaps of iron atoms.

The Hydroxyde S of Fer are found mixed, in a microcrystalline state, in the Limonite or brown hematite and constitute the “Chapeau of iron”. It is about a sedimentary ore of origin which contains Goethite, Lépidocrocite and in small quantities of the Hématite, Hydroxyde S of Aluminum, colloidal Silice, minerals Argile ux, Phosphate S, Arséniate S, as well as organic compounds. In fibrous masses, the Limonite is rather pure, but at the time it is presented in compact or earthy masses, it loses its iron and steel share, because it contains Sulfure S (of Fer, but also of the Plomb), phosphates and arsenates. In France, there exists little of limonite, but one finds some with the the United States, in Russia and Scandinavia.

The Ilmenite, mineral with structure of Hematite, is used rather for the extraction of the Titane, iron having additional interest.

The Silicate S are not used for the extraction of iron, because the process of enrichment is complex.

See too

Lorraine Iron ore

Nds-nl: Oer

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