Explanation
I ) Hall – Heroult process is the major industrial process for smelting aluminium. It involves dissolving aluminium Oxide(alumina) in molten cryolite, and electrolysing the molten salt bath, typically in a purpose – built cell.
II ) The Baeyer’s process is the prinicipal industrial means of refining bauxite to produce alumina (aluminium oxide). Bauxite, the most important ore of aluminium contains only 30 –54% aluminium oxide (Al2O3), the rest being a mixture of silica, various iron oxides and titanium dioxide.
III ) Serpeck’s process is used for the purification of bauxite ore conatining silica (SiO2) as the main impurity. During this Aluminium nitride will form.
In order to remove infusible impurities a suitable substance known as Flux is added during reduction process to convert infusible impurities to fusible material, which is known as slag. The slag is lighter than molten metal hence it floats over metal and is removed from slag hole.
Ore + gangue + reducing agent + flux + heat →metal + slag + Gases
The nature of the flux used depends on nature of impurity to be removed. An acidic flux is used to remove basic impurity.
FeO + SiO2 → FeSiO3
(Basic impurity) (Acidic Flux) (Fusible slag)
A Basic Flux is used to remove acidic impurity
SiO2 + CaO → CaSiO3
(Acidic impurity) (Basic flux) (Fusible slag)
Some ores are self fluxing because they contain some gangue which is itself fusible and no foreign flux is required.
In smelting, metal is obtained in a fused state.
Sulphide ore of zinc/copper is concentrated by floatation process.
Pig iron is an impure form of iron and not an ore.
In Van-Arkel method, the metal is converted into its stable volatile iodide which is then decomposed at higher temperature to pure metal and I2.
Smelting involves heating of oxide of the metal with carbon or coke at very high temperature.
Both Ca and K are highly electropositive metals. When heated with C they form carbides.
Pine oil is adsorbed at the surface of sulphide ore particles which become water repellant and come out along with froth when air is blown through the mixture.
Highly electropositive elements are extracted by electrolytic reduction
In froth floatation process, ore particles float because their surface is hydrophobic i.e., not easily wetted by water but wetted by oil.
Chalcopyrites are sulphide minerals which are concentrated by froth floatation process.
In smelting, ore is reduced by C or other reductants in molten state
Mg and Al are highly electropositive metals and can not be obtained by electrolysis of the aqueous solution of their salts as they would react with water.
FeCrO4 being magnetic in nature can be separated from tin ore (SnO2) which is non magnetic by magnetic separation method.
Non metals form oxides with oxygen and thus reduce oxides of metals behaving reducing agents.
Al2O3.2H2O (bauxite) is concentrated by leaching with NaOH.Al2O3 dissolves leaving other impurities undissolve.
Al2O3.2H2O + 2NaOH → 2NaAlO2 + 3H2O
In blast furnace, zone of combustion has 1500–1600ºC temperature, zone of fusion (1200–1500ºC), zone of heat absorption, middle zone (800-1200ºC) and zone of reduction (300–700ºC) are other zones of the furnace.
Calcination is used to remove organic matter, water from hydrated oxides and Co2 from carbonates.
Electrolysis is done to achieve electroplating and electrorefining of metals.
In electrorefining of copper, impure copper is made anode while pure Cu strip is made cathode. On passing current impurities like Fe, Zn, Ni, Co dissolve in the solution and Au, Ag etc. settle down below as anode mud.
Silicon is purified by zone refining process.
Argentite is Ag2S and cuprite is Cu2O.
Lustre of metals is due to the presence of mobile electrons.
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