An ore is a mineral aggregate in which the share of a useful component or more of them is such as to justify its economical exploitation. Iron ores are profitable for exploitation if they contain min. 25-30% Fe.
According to their chemical composition, iron ores are divided into:
• oxide: magnetite (Fe3O4) - about 72% Fe, hematite (Fe2O3) - about 70% Fe, limonite (FeO (OH) - about 50… 66% Fe
• carbonate: siderite (FeCO3) - about 48% Fe
• silicate: chamosite (Fe, Mg) 5Al (Si3Al) O10 (OH) 8
• sulfide: pyrite (FeS2).
Iron ore consists of a useful part (all components containing iron), companions (various elements bound to the useful part) and tailings (compounds that are mechanically bound to the useful part). Today, the following methods are used for the production of pig iron:
• blast furnace (approx. 95% of total production)
• electro-reduction furnace (approx. 2 (3%)
• direct reduction (approx. 2… 3%). Production of pig iron 6
• stage of production of pig iron from the blast furnace. - physical (tailings removal, crushing) and - chemical (drying, frying, etc.) The process of production of pig iron from ore.
The process of production of pig iron from ore takes place in two stages:
• phase of preparation of iron ore for metallurgical processing
- physical (tailings removal, crushing) and
- chemical (drying, frying, etc.)
• stage of production of pig iron from the blast furnace.
The prepared ore together with the smelting additives and reducing agents comes into the blast furnace for the production of pig iron.
Melting additives (limestone CaCO3 - for acid tailings or quartz sand SiO2 - for basic tailings) bind ash and tailings from the ore during the process. This produces an easily melting mass of lower density than the molten iron, which collects on the surface and is discharged as slag.
Coke (most often), natural gas, oil and powdered coal are used as reducing agents (carbon carriers). Coke in the blast furnace also serves as a carrier of the thermal energy of the process.
The production of steel in the blast furnace begins with the processes of reduction (release of oxygen) of iron ore.
The reduction takes place directly using carbon from coke (eg Fe3O4 + 4C → 3Fe + 4CO) or indirectly via CO (FeO + CO → Fe + CO2). Reduced (molten) iron in contact with coke, limestone, flint, air and refractory wall of the furnace dissolves certain amounts of carbon, part of the accompanying elements (Mn and Si) and impurities (P and S).
The product of the blast furnace is white or gray pig iron with a relatively high mass fraction of carbon (2… 4% C), phosphorus and sulfur and other impurities (6… 10%). Due to the high mass fraction of carbon and phosphorus, pig iron is brittle and unusable for technical applications. On a ton of pig iron comes a ton of by-product of slag (slag) which serves as a base for backfilling, for making mineral wool, cement and fertilizer.