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Tuesday, 29 January 2013

Copper , Lead , Magnesium , Aluminium Extraction Metallurgy.

Copper , Lead ,  Magnesium , Aluminium Extraction Metallurgy in Animated form

Bessemer Converter



Natural Copper Ores

Copper occurs in the native state as well as in the compounds form.The natural ores of copper are :

      Copper pyrites, CuFeS2                                                   Malachite , Cu(OH)2. CuCO3
      Cuprite or ruby copper, Cu2O                                               Azurite,Cu(OH)2. 2CuCO3
      Copper glance , Cu2S


Natural Lead Ores

Lead is widely distributed in nature . it is the stable end product of all natural radioactive elements. It occurs in traces in the native form . In the combined form , it occurs as :

      Galena ,PbS                                                                               Cerussite PbCO3
      Anglesite, PbSO4                                                                                              Wulfenite, PbMnO4
      Stolzite, PbWO4

Both copper and lead may be extracted by self-reduction method.

Extraction of Copper:

Copper is mainly extracted from the copper pyrites.After the concentration of its ore by froth floatation process, the ore is roasted in a current of air to remove arsenic , antimony and much of sulphur.The reaction occurring are : 

1)   2CuFeS2 + O2 ----> Cu2S + 2FeS + SO2  ^   (major reaction)

2)   2Cu2S + 3O2  -----> 2Cu2O + 2SO2

3)   2FeS + 3O2 ------> 2FeO + 2SO2                        (minor reaction)

The ore is then mixed with a little coke and sand and smelted in a water jacketed blast furnace . The minor reactions that occurred during the roasting continue here.Ferrous oxide combines with sand to form a fusable cuprous oxide formed combines with ferrous sulphide to give ferrous oxide and cuprous sulphide.This is because iron has more affinity for oxygen than copper.

4)  FeO + SiO2 ------> FeSiO3

5)  Cu2O + FeS ----> Cu2S + FeO

Molten mass collected from the bottom of furnace contains largely cuprous sulphide and a little ferrous sulphide . This molten mass is known as matte.
The molten matte is finally transferred to Bassemer converter. A blast of sand and air is blown in the converter through tuyeres which are situated a little above the bottom.This causes removal of S and As as oxides and ferrous oxide as slag.At the same time Cu2S  is oxidized mostly intoCu2O  and partly into CuO and CuSO4 all these react with Cu2S giving copper. The reactions are:

          2) 2Cu2S + 3O2  -----> 2Cu2O + 2SO2 ^
               2Cu2S + 5O2 ------> 2CuSO4 + 2CuO
               2Cu2O + Cu2S ------> 6 Cu + SO2 ^
               CuSO4 + Cu2S ------> 3Cu + 2SO2 ^
                Cu2S + 2CuO -------> 4Cu + SO2 ^

Finally copper may be refined electrolytically (electrolyte; copper sulphate : anode; impure copper and cathode;pure copper).

Extraction of Lead:

Lead is mainly extracted from Galena. After the concentration of the ore by froth floatation process , the ore is roasted in a reverberatory furnace for about six hour at a moderate temperature in a current of air. part of Galena is converted into lead oxide and lead suphate giving metallic lead:

   PbS + PbO ------> 3Pb + 2SO2
   PbS + PbSO4 -------> 2Pb + 2SO2

The obtained lead contains impurities such as Cu, Ag, Bi, Sb, and Sn.Silver is removed by Parke`s process where molten Zn is added to molten impure lead.The former is immiscible with the latter.Silver is more soluble in molten zinc tha in molten lead.Zinc -silver alloy solidified earlier than molten lead and thus can be separated. After this crude lead is refined electrolytically .


Magnesium Minerals Ores


Magnesium does not occur in the native state . Its important minerals are

     Magnesite MgCO3                                                            Dolomite, MgCO3 ,CaCO3 
     Carnallite, MgCl2 . KCl . 6H2O                            Epsomite(epsom salt), MgCO3 . 7H2O
     Kiesserite MgSO4 . H2O                                                   Kainite, MgSO4 . KCl . 3H2O
     Schonite MgSO4 . K2SO4 . 6H2O

Magnesium is widely distributed in nature, in rocks, spring and seawater. In rocks and silicates it occur in mineral like Olivine (Mg2SiO4) , talc
(Mg3H2(SiO3)4) , asbestos (CaMg3(SiO3)4) etc.

Aluminium Compound Ores

Aluminium also does not occur free in nature .In the combined state, it occurs in the following forms:

    Oxides: Corundum, Al2O3 ; diaspore, Al2O3 . H2O and bauxite,  Al2O3 . 2H2O

    Fluorides: Cryolite, Na3AlF6

    Silicates: Feldspar, KAlSi3O8, Mica (KAlSi3O10(OH)2) and Kaolinite (Al(OH)4 . Si2O5)

    Basic Sulphates:  Alunite or alnumstone K2SO4 . Al2(OH)3 . H2O

    Basic Phosphate: Turquoise, AlPO4 . Al(OH)3 . H2O

    Aluminates: Aluminates of Mg, Fe and Mn

Aluminium is the third most abundant element of earth`s crust.

Extraction of Magnesium:

Electrolytic Cell for The Production of Magnesium


Magnesium is commonly obtained by the electrolysis of fused magnesium chloride containing little sodium chloride and sodium fluoride at 700 degree C in an air tight iron pot which itself serves as the cathode, the anode being a graphite rod which dips into the electrolyte.The anode is surrounded by a perforated porcelain tube for the exit of chlorine. The electrolysis is carried out in the atmosphere of coal gas so as to prevent the attack of atmospheric oxygen and nitrogen on magnesium. Molten Magnesium being lighter than the electrolyte, it floats over the fused electrolyte and is withdrawn.

In Daw Process, Magnesium is recovered from seawater as magnesium chloride which is then electrolysed using the cell as picture shown.

Anhydrous Carnallite(KCl . MgCl2 .  6H2O) May also be employed as the starting material of Magnesium chloride . The cathode may be a layer of molten lead on the floor of the cell and anode may be graphite rods which are suspended above the molten lead. Magnesium liberated at the cathode dissolves in molten lead.The alloy of lead-Magnesium is subjected to electrolysis to obtain pure magnesium.

 Extraction of Aluminium:

Electrolytic Cell For The Production of Aluminium

Aluminium is isolated from the electrolysis of bauxite Al2O3 . 2H2O . Since it is difficult to purify aluminium, bauxite ore is purified either by baeyer`s process( Hall`s process) or Serpec`s Process depending upon the impurity present in the ore.If the bauxite contains iron oxide as the impurity, one can use Baeyer`s or Hall`s process as described below.

Baeyer`s Process:

Finally the ground ore is roasted to convert ferrous oxide to ferric oxide and then digested with concentrated caustic soda solution at 423 K. Al2O3
dissolves while Fe2O3 remains undissolved .The later is filtered off and from the solution Al(OH)3 is precipitated by adding a weak acid. The Ignition of 
Al(OH)3 gives Al2O3

      Al2O3  + 2OH(-) + 3H2O ------->2Al(OH)4(-)  (aluminium ion dissolves)

      Al(OH)4(-) + H(+) -------> Al(OH)3 + H2O
        2Al(OH)3 -------> Al2O3  + 3H2O

Hall`s Process:

In this process the ore is fused with sodium carbonate when soluble meta-almunate (NaAlO2) is produced. This extracted with water leaving behind iron oxide. Carbon dioxide at 323 - 333 K is passed through water extract to get Al(OH)3 which on heating gives Al2O3 .
 Al2O3  + Na2CO3 --------> 2NaAlO2 + CO2
                                     Extracted with water

2NaAlO2 + 3H2O + CO2 ------> 2Al(OH)3  + Na2CO3
2Al(OH)3 ------------> Al2O3  + 3H2O

If the impurity is the silica , the Serpek`s process is used to purify Bauxite.

Serpek`s process:

The powdered ore is mixed with coke and heated to 2075 K in a current of nitrogen , Silica present is reduced to silicon which Volatilizes off and alumina gives aluminium nitride.The hydrolysis of the latter gives Al(OH)3 , heating of which gives Al2O3 .

        SiO2 + 2C ----> Si ^  + 2CO2 ^
        Al2O3 + 3C + N2 ------> 2AlN + NH3
        AlN + 3H2O ----> Al(OH)3 + NH3
        2Al(OH)3  ---------> Al2O3 + 3H2O

After obtaining pure Al2O3 it is dissolved in fused cryolite, Na3AlF6, with a little fluospar, CaF2. And eletrolysed in an iron tank lined with blocks of carbon which serve as the cathode.The anode consists of a number of graphite rods suspended vertically inside the tank.Aluminium get settled at the bottom of the tank and can be removed .The reactions ocurring at the electrodes are

     Cathode :   Al(3+)  + 3e(-) -----> Al

      Anode    :   2O2(2-) ------> O2 + 4e(-)
                           C + O2 --------> CO2

Anode is replaced periodically because of its consumption.

Copper , Lead ,  Magnesium , Aluminium Extraction Metallurgy.

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