-Those elements which can show some properties of metals and some properties of nonmetals.
-These are also called border line elements because they lies in between metal and non-metal in the periodic table.
-E.g. , etc.
-They can form acidic oxides like non-metals and can conduct heat and electricity like metals.
-The naturally occurring substances which contains metal in it are known as minerals.
-Eg: Rock, Clay, etc.
-The minerals from which we can extract the metal in economical as well as efficient way are known as Ores.
- Whole proportion of ore can be used to extract metal.
-Every ore is a mineral but every mineral is not an ore.
-They are the homogeneous mixture of metals with metals or metals with non-metals.
-But the homogeneous mixture of non-metal and non-metal is not called alloy.
-Types of Alloys:
i)Ferrous: Contains Iron in it. Eg: Steel, Stainless steel
ii)Non-Ferrous: Doesn't contain Iron in it. Eg: Brass, Bronze, etc.
-The homogeneous mixture of Mercury with metal is known as amalgam.
-Eg: , [Sodium amalgam]
-, [Copper amalgam] (Used for filling cavity in teeth.))
-Metals like Iron , Cobalt and Nickel doesn’t form amalgam because they do not dissolve in Mercury.
-The unwanted earthy particles present in the ore are called Gangue.
-Flux are the substances added for the removal of refractory impurities.
-Acidic Flux: The flux used for the removal of basic impurities is known as acidic flux. E.g. , .
-Basic flux: The flux used for the removal of acidic impurities is known as basic flux. E.g. , , , etc.
-Neutral flux: The flux is used to maintain the fluidity of melted substance. Eg:
-The resulting compound obtained after treating the refractory impurity with suitable flux is called slag.
- The melting point of slag is low. So, it can be fused easily.
-(Slag= Flux + Gangue)
-Process that is used for the extraction of metal in their pure form from their respective ores.
-Process in which reduction of ore is carried out in higher temperature.
-Eg: , etc.
-Process in which ore is converted into soluble form followed by reduction.
-Process in which electrolytic reduction is carried out.
-Eg: For most electro +ve metals like Alkali metal, Alkaline earth metal, etc
- The first process in metallurgy is crushing of ores into a fine powder in a crusher or ball mill. This process is known as pulverization.
-The process of removing impurities from ore is known as a concentration of minerals or ore dressing. In metallurgy, we concentrate the ores mainly by the following methods.
-In this method, we pour the ore over a sloping, vibrating corrugated table with grooves. A jet of water is allowed to flow over the surface. The denser ore particles settle in the grooves, and the impurities are washed away by water. Eg: Bauxite ore of aluminum, Hematite or Magnetite of Iron etc.
-In this case, the crushed ore is placed on a conveyor belt. This belt rotates around two wheels in which one of the wheels is magnetic, and therefore the magnetic particles get attracted to the magnetic wheel and fall apart from the non-magnetic particles.
-In this process, we take the crushed ore in a large tank which contains oil and water. A current of compressed air is passed through it. The ore gets wet by oil and is separated from the impurities in the form of froth. Ore is lighter, and so it comes on the surface and impurities are left behind. Eg: , etc.
-If one of impurities or ore be magnetic and another is non-magnetic then such types of ores can be concentrated by using electromagnetic separation. On passing the ore in rotating belt magnetic particles will be attracted by magnetic rotator collected near the rotator. Whereas non-magnetic particles will be collected away from rotator.
-In this method powdered ore is treated with suitable chemical (Acid, Base) so that metallic portion present in given ore get dissolved with chemical but impurities don’t get dissolve. By filtration impurities can be separated as a residue while a filtrate will contain the metallic portion. From filtrate concentrated ore can be recovered by suitable chemical technique like precipitation. Generally, ores of Aluminum, gold and silver can be concentrated by leaching.
-It is the process of heating a concentrated ore in the absence of air below the melting point of ore. The purpose of calcination is to convert a concentrated ore into oxide form. Calcination is mainly carried out for oxides, hydroxides, carbonates and Nitrate ores. During calcination following changes takes place.
a) Moisture gets removed.
b) Volatile impurities gets removed.
c) Water of crystallization gets removed
d)Decomposition of ores may also take place
-It is the process of heating a concentrated ore in the presence of ore below the melting point. The purpose of roasting is to convert a concentrated ore into oxide form. It is mainly carried out for the oxidation of sulphide ores.
During roasting similar changes take place
a)Oxidation of ores takes place
b) Mixture volatile impurities and organic matters get removed.
c) Elements like etc. gets oxidized.
-Metals can be extracted from metallic oxide removing oxygen present in the metallic oxide.
-Such process of removal of oxygen with the help of suitable reducing agent is known as reducing.
-Depending upon the nature of metal reduction can be carried out by chemical method or electrolytic method.
There are two types of reduction they are:
-In this method, reduction is carried out by using suitable chemicals like Carbon, Aluminum, Hydrogen, water gas etc. depending upon the reactivity of metal, chemical method of reduction can be carried out in the following ways:
a) Reduction with Carbon:
-Metals which lies in central or lower position in electrochemical series can be extracted by using carbon as a reducing agent.
-In this method calcined or roasted ore is mixed with Carbon (as a source of Carbon we can use coke, coal or charcoal) along with suitable flux. On providing a sufficient heat, reduction proceeds and metal is obtained in a molten state. So, this method is also known as smelting.
-Flux combines with impurities resulting a slag which also exist in molten state. Taking an advantage of immiscibility of slag with metal. Slag can be removed easily and almost pure metal is obtained.
-In certain case, carbon monoxide gets formed in situ which helps for the reduction of remaining oxide.
-Refractory impurities get removed with flux resulting a slag.
-E.g. During extraction of Fe, an ore may contain as a refractory impurity so acidic flux like is added for the removal of impurity.
b) Reduction with Aluminum
-Metallic oxides in which Oxygen has strong affinity with metal than Carbon, such type of oxides can’t be reduced by Carbon. So, aluminum which is powerful reducing agent than carbon can be used as a reducing agent instead of Carbon.
-Generally metals like Manganese, Chromium and Nickel used to be extracted by this method.
- In this method, roasted ore is thoroughly mixed with Aluminum powder along with little amount of Barium Peroxide and kept in a suitable crucible fitted with magnesium ribbon. Heat energy required to initiate reduction is supplied by burning of BaO2 and magnesium ribbon.
- Once the reduction is started, heat is evolved inside a crucible because the reaction is exothermic in nature.
-In this process also metal is obtained in molten state.
-Highly reactive metals like and etc. can’t be extracted from their oxide by chemical method of reduction because in order to reduce their oxide there is necessary of huge amount of heat and at very high temperature these metals forms an undesired products.
-Extraction of such metal can be done by carrying out an electrolysis of molten salt.
- During electrolytic reduction aqueous solution of salt can’t be used because moisture is easily captured by metals and ferrous hydroxide, after electrolysis of molten salt metal is collected at cathode.
-E.g. Na can be extracted by electrolysis of molten NaCl. During this process, is collected from the cathode.
-Metals obtained by the chemical method of extraction is not in the pure state. Following impurities may be associated with metals.
i) Residual slag or flux.
ii) Metals other than the desired one.
iii) Unreduced metallic ores.
iv) Elements like etc.
In order to remove such types of impurities, metals should be purified.
Depending upon a nature of impurities following methods can be applied for the purification.
Metals with comparatively lower boiling point can be purified by carrying out distillation. Generally , (cadmium), can be purified by this process. In this process metals with low boiling point distilled out first and impurities remains in retort.
Metals with low melting point can be purified by heating in a sloping furnace. After heating metal with low melting point, it melts earlier and drains down while impurities remains unchanged in furnace. E.g. , .
Impurities present in metal can be removed by heating an impure metal in the presence of air. During heating, stirring of molten metal is done so that impurities get oxidized.
In this process molten metal is stirred with pole of green wood. Hydro carbon present in green wood acts as reducing agent so that oxide impurities get reduced into respective metal. This method is specially used for purification of Copper.
This method is cheap and convenient metals like , , and can be refined electrolytically. The impure metal is made anode and a thin strip of pure metal is made cathode in electrolytic cell. The cell is filled with solution of suitable salt of concerned metal or passing electricity, pure metal gets deposited at cathode as the anode undergoes dissolution. Insoluble impurities fall behind the anode in the form of anode mud and soluble impurities go to the solution.