The metals extracted from various reduction process is not very pure Why?
Answers
The process of extracting a metal in pure form from its ore is known as metallurgy. The process of treatment depends on upon the nature of the ore, impurities, and the metal.
From the extraction point of view, the metals can be broadly classified into five categories.
Category I :Highly electropositive metals such as alkali metals are extracted by the electrolytic method from their molten/fused salts.
Category II :Electropositive metals such as alkaline earth metals are extracted by electrolytic method form their molten salt.
Category III : Reactive metals of high valency are extracted by reduction and electrolytic method.
Catagory IV :Heavy metals such as Fe, Co, Ni , Cu , etc . are extracted by roasting and reduction methods.
Catagory V :Less reactive metals such as Ag, Au, Pt, etc. are extracted by amalgamation or cyanide process.
The various process involved in the extraction of pure metals from their ores are :
Concentration or Benefaction of the ore
Extraction of crude metal from the concentrated ore
Refining of the crude metal.
A. Concentration or Benefaction of the Ore
This is a very important in metallurgy. The ore is obtained from the earth and usually contain dust, stone, quartz, feldspar and other foreign materials.These impurities are known as gangue or matrix. The process of separation of gangue from ore is known as concentration. The important process of concentration is discussed below .
Crushing and grinding of the ore
Big lumps of ore are first broken into small pieces by the means of mechanical crusher or by hammering. The crushed ore is then ground in a ball mill or a roller mill or a stamp mill. The powdered ore is passed through sieves of the particular size and remains of the sieves are further pulverized in a ball mill or a stamp mill to get ultimately fine dust like powder of theor.
Gravity separation or Levigation
This method depends on the specific gravity of metallic ore and the earthy impurities. The powdered ore is washed with an upward stream of running water. The lighter gangue particles are washed away while the heavier ore particles settle down and are removed from the base. Generally, oxides like the tin stone (SnO2), haematite (Fe2O3) are concentrated by this method.
