General Methods of Extraction or Extraction Metallurgy



General Methods of Extraction

Extraction metallurgy is divided into three fields namely:

(1) Pyrometallurgical Unit Operations (Fire metallurgy)

Pyrometallurgy covers metallurgical operations that involve processing at temperatures substantially above ambient conditions, generally involving chemical reactions as distinct from metal casting which involves only a physical transformation (i.e. solidification). Some important metals such as Iron and steel, nickel and tin are exclusively produced with this method. Pyromet unit operations include calcining, roasting, reduction, smelting. refining and recycling.

Calcining

It involves the decomposition of a mineral and removal of (CO2, water, organic matter etc. )

CaCO3 →  CaO + CO2

Roasting

This is carried out at high temperature but it involves the combination of the heating gases with the minerals. It is usually an oxidizing process.

Sintering

The agglomeration of fine particles at high temperatures is called sintering.

Smelting

It is that process in which the oxides get reduced to give molten metals

2. Hydrometallurgy

This branch of metallurgy, deals with the extraction of metals by dissolving or leaching out the metal or its compounds from the ore with the help of a selective solvent. The solution is separated from the undissolved material and the metal is recovered from the leach liquor by electrolysis or by precipitation with a suitable metal.

3-Thermo-Electrical Metallurgy

Electrometallurgy involves processing with the passage of electrical current; it can be in an aqueous system or can be at temperatures substantially above ambient conditions in fused salt systems, it generally involves chemical reactions to either precipitate a metal from the liquid phase or to refine a metal by transferring the metal from an anode to a cathode leaving the impurities in the anode behind. This process is expensive and is applied only if pyrometallurgical or hydrometallurgical methods fail due to one reason or the other. Thus the production of aluminium and magnesium, beryllium, sodium and calcium is exclusively based on this method. All of these metals are highly reactive and it is not possible to extract them under ordinary conditions by electro deposition from solution. The electrolysis of the molten mass is therefore carried out.

Now the ores have been concentrated, the subsequent steps for the production of metals vary depending upon their nature and types of ore. Therefore, the other metallurgical operations will be discussed along with the metallurgy of the corresponding metal.

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