Online Notes on "General Principles & Processes Of Isolation of Elements" (Chapter=>6 ) Part 1

These are Online Notes on "General Principles & Processes

Of Isolation of Elements" (Chapter=>6 ) Part 1 for practice of CBSE BOARD, CBSE NEET, CSIR NET Chemical Sciences etc.

1. Minerals: The naturally occurring chemical substances in the earth’s crust which are obtained by mining are known as minerals. Metals may or may not be extracted profitably from them.

2. Ores: The rocky materials which contain sufficient quantity of mineral so that the metal can be extracted profitably or economically are known as ores.

3. Gangue: The earthy or undesirable materials present in ore are known as gangue.

4. Metallurgy: The entire scientific and technological process used for isolation of the metal from its ores is known as metallurgy.

5. Chief Ores and Methods of Extraction of Some Common Metals:

Metals	Occurrence	Extraction Method				Remark
Sodium	Rock salt: NaCl	Electrolysis of fused			Sodium		is	highly
	Feldspar:Na3AlSi3O8	NaCl or NaCl/ CaCl2			reactive,		it  reacts		with
					water
Copper	Copper pyrites:CuFeS2	Roasting	of	sulphide	It is self reduction in a
	Malachite:CuCO3.Cu(OH)2	partially and reduction			specially			designed
	Cuprite: Cu2O	2Cu2O + Cu2S → 6 Cu			converter.			Sulphuric
	Copper glance: Cu2S			+SO2	acid	leaching  is			also
					employed.
Aluminium	Bauxite: AlOx(OH)3-2x	Electrolysis    of    Al2O3			A	good	source		of
	where 0<x<1	dissolved	in	molten	electricity		is	needed  in
	Cryolite: Na3AlF6	cryolite or in Na3AlCl6			the extraction of Al
	Kaolinite: [Al2(OH)4Si2O5]
Zinc	Zinc blende or Sphalerite:	Roasting	and	then	The	metal		may	be
	ZnS	reduction with C			purified		by	fractional
	Zincite: ZnO				distillation.
	Calamine: ZnCO3
Lead	Galena: PbS	Roasting of the sulphide			Sulphide			ore	is
		ore  and	then  reduction		concentrated			by	froth
		of the oxide			floatation process
Silver	Argentite: Ag2S	Sodium cyanide leaching			It	involves		complex
		of the sulphide ore and			formation				and
		finally replacement of Ag			displacement
		by Zn

Metals	Occurrence	Extraction Method				Remark
Sodium	Rock salt: NaCl	Electrolysis of fused			Sodium		is	highly
	Feldspar:Na3AlSi3O8	NaCl or NaCl/ CaCl2			reactive,		it  reacts		with
					water
Copper	Copper pyrites:CuFeS2	Roasting	of	sulphide	It is self reduction in a
	Malachite:CuCO3.Cu(OH)2	partially and reduction			specially			designed
	Cuprite: Cu2O	2Cu2O + Cu2S → 6 Cu			converter.			Sulphuric
	Copper glance: Cu2S			+SO2	acid	leaching  is			also
					employed.
Aluminium	Bauxite: AlOx(OH)3-2x	Electrolysis    of    Al2O3			A	good	source		of
	where 0<x<1	dissolved	in	molten	electricity		is	needed  in
	Cryolite: Na3AlF6	cryolite or in Na3AlCl6			the extraction of Al
	Kaolinite: [Al2(OH)4Si2O5]
Zinc	Zinc blende or Sphalerite:	Roasting	and	then	The	metal		may	be
	ZnS	reduction with C			purified		by	fractional
	Zincite: ZnO				distillation.
	Calamine: ZnCO3
Lead	Galena: PbS	Roasting of the sulphide			Sulphide			ore	is
		ore  and	then  reduction		concentrated			by	froth
		of the oxide			floatation process
Silver	Argentite: Ag2S	Sodium cyanide leaching			It	involves		complex
		of the sulphide ore and			formation				and
		finally replacement of Ag			displacement
		by Zn

6. Steps of metallurgy:

a. Concentration of ore

b. Conversion of concentrated ore to oxide

c. Reduction of oxide to metal

d. Refining of metal

7. Concentration of ore: The process of removal unwanted materials like sand, clay, rocks etc from the ore is known as concentration, ore – dressing or benefaction. It involves several steps which depend upon physical properties of metal compound and impurity (gangue). 

The type of metal, available facilities and environmental factors are also taken into consideration.

8. Hydraulic washing (or gravity separation): It is based on difference in densities of ore and gangue particles. Ore is washed with a stream of water under pressure so that lighter impurities are washed away whereas heavy ores are left behind.

9. Magnetic separation: This method is based on the difference in magnetic and non – magnetic properties of two components of ore (pure and impure). This method is used to remove tungsten ore particles from cassiterite (SnO₂). 

It is also used to concentrate magnetite (Fe₃O₄), chromite (FeCr₂O₄) and pyrolusite (MnO₂) from unwanted gangue.

10. Froth Floatation Process: The principle of froth floatation process is that sulphide ores are preferentially wetted by the pine oil, whereas the gangue particles are wetted by the water. 

Collectors are added to enhance the non-wettability of the mineral particles. 

Examples are pine oil, fatty acids and xanthates are added to it. Froth stabilizers are added to stabilize the froth. 

Examples are cresols, aniline. If two sulphide ores are present, it is possible to separate the two sulphide ores by adjusting proportion of oil to water or by adding depressants.

For example- In the case of an ore containing ZnS and PbS, the depressant used is NaCN. It selectively prevents ZnS from coming to froth but allows PbS to come with the froth.
Click HERE for Online Notes on "General Principles & Processes Of Isolation of Elements" (Chapter=>6 ) Part 2