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The materials which can withstand very high temperatures without melting or becoming soft are known as refractory materials. These are not affected by slags formed during the extraction of metals. These are used in the form of bricks for the internal linings of furnaces. Refractory materials used are of three types,   (1) Acid refractories : Silica, quartz, silicious sand stones, etc., are the examples.   (2) Basic refractories : Lime, dolomite, magnesite, etc., are the examples.   (3) Neutral refractories : Graphite, chromite, bone ash, etc., are the examples.     Silica \[(92%\ Si{{O}_{2}},\ 2.7%\ A{{l}_{2}}{{O}_{3}})\] and quartz, can tolerate temperatures upto about \[{{1750}^{o}}C,\] bauxite upto \[{{1800}^{o}}C,\] alumina upto \[{{2000}^{o}}C\] and magnesite, chromite, etc., upto \[{{2200}^{o}}C\]. Some carbides such as silicon carbide is used as refractory for special purposes.  

In the extraction of metal different types of furnaces are used. Each furnace has its own characteristics. Some principal furnaces have been described below,   (1) Blast furnace : It is a special type of tall cylindrical furnace, about 100 feet high with a diameter of 15-28 feet. It is made of steel sheets lined inside with fire-proof bricks. The charge is added through a cup and cone arrangement at the top. At the upper part of the furnace there is a hole for the escape of the waste gases of the furnace. There are two outlets in the hearth of the furnace, one for tapping the molten metal and the other above it for the slag. The waste gases are heated and a hot air blast under pressure is blown into the furnace by means of bellows or fans through water cooled nozzles ortuyers. The temperature of the furnace varies from \[{{250}^{o}}C\]to \[{{1500}^{o}}C\]. Thus the charge descends slowly into zone of increasing temperatures. The blast furnace is used for the extraction of metal like copper and iron.     (2) Reverberatory Furnace : In this furnace fuel burns in a separate part and does not mix with the charge. The furnace may be divided into 3 parts,   (i) Fire Grate : It is on one side where the fuel burns.   (ii) Flue or Chimney : It is on the other side of the fire grate. The waste gases escape through it.   (iii) Hearth : It is the middle part of the furnace where the charge is heated with the flames and hot gases.   The material to be heated is placed on the hearth or bed of the furnace and is heated by the hot gases or flames produced by the burning of fuel. The waste gases escape out of the chimney. Since the fuel does not come in contact with the charge, the furnace is very suitable for calcination and roasting and is employed for both oxidising and reducing purposes. For oxidation, the material is heated by the current of hot air while for reduction the material is mixed with coke and heated. The furnace find wide application in the extractive metallurgy.       (3) Electric Furnace : The fuel burnt furnaces described in this chapter produce temperature in the range of \[1000-{{1500}^{o}}C\]. Although these furnaces have the great utility in the extraction of metals yet these are unsuitable where higher temperatures are needed. One commonly used electric furnace is Heroult’s furnace shown in fig. It consists of a steel shell lined inside with dolomite or magnesite. It is provided with movable water jacketed electrodes suspended from the roof or from the sides. Heat is generated by striking an arc between the electrodes, thereby, a temperature of over \[{{3000}^{o}}C\] may be reached. The charge melts and the impurities e.g., Si, Mn, P and S etc. present in the more...

Different metallurgical processes can be broadly divided into three main types               (1) Pyrometallurgy : Extraction is done using heat energy. The metals like \[Cu,\,Fe,\text{ }Zn,\,Pb,\,Sn,\,Ni,\,Cr,\,Hg\] etc. Which are found in the nature in the form of oxides, carbonates, sulphides are extracted by this process.               (2) Hydrometallurgy : Extraction of metals involving aqueous solution is known as hydrometallurgy. Silver, gold etc are extracted by this process.                   (3) Electrometallurgy : Extraction of highly reactive metals such as \[Na,\,K,\,Ca,\,Mg,\,Al\] etc. by carrying electrolysis of one of  the suitable compound in fused or molten state.  

The extraction of a pure metal from its ore is called metallurgy. In order to extract the metal from ores, several physical and chemical methods are used. The method used depending upon chemical properties and nature of the ore from which it is to be extracted. It involves four main steps,   (1) Crushing and grinding of the ore.   (2) Concentration or dressing of the ore.   (3) Reduction to free metal.   (4) Purification or refining of the metal.   (1) Crushing and grinding of the ore : Those ores occur in nature as huge lumps. They are broken to small pieces with the help of crushers or grinders. These pieces are then reduced to fine powder with the help of a ball mill or stamp mill. This process is called pulverisation.   (2) Concentration or dressing of the ore : The ore are usually obtained from the ground and therefore contained large amount of unwanted impurities, e.g., earthing particles, rocky matter, sand, limestone etc. These impurities are known collectively as gangue or matrix. It is essential to separate the large bulk of these impurities from the ore to avoid bulk handling and in subsequent fuel costs. The removal of these impurities from the ores is known as concentration. The concentration is done by physical as well as chemical methods.   Physical Methods (i) Gravity Separation or levigation: This process of concentration is based on the difference in the specific gravity of the ore and gangue. The sieved ore is either subjected to dry centrifugal separation or is placed in big shallow tanks in which a strong current of water blows. Heavy ore particles settle down to the bottom of the tanks while lighter gangue particles are carried away by the current of water. The process removes most of the soluble and insoluble impurities. For this purpose wilfley table and hydraulic classifier are widely used. The method is particularly suitable for heavy oxide and carbonate ores like Cassiterite \[(Sn{{O}_{2}})\] and haematite.       (ii) Froth floatation process : In some cases for example, sulphides ores of copper, zinc and lead concentration is brought by this method. In this method advantage is taken of the preferential wetting of the ore by an oil. The finely ground ore is taken in a tank containing water and 1% of pine oil or terpentine oil. A strong current of air is blown through the suspension, producing a heavy froth or foam on the surface. The metal sulphide is wetted by the oil but the gangues is not and the sulphide-oil mixture is carried to the surface by films of oil The froth is skimmed off, the gangue settles down on the bottom or remains underneath the froth. By this floatation method it is possible to concentrate over 90% of a sulphite ore to 1/10 of its original bulk.       (ii) Activators and Depressants more...

Metals are also found in living organisms, e.g.,          (1) Magnesium is found in chlorophyll.                                 (2) Potassium is present in plant roots.            (3) Manganese, Iron and copper are present in chloroplast.                (4) Zinc is present in eyes of cats and cows.            (5) Iron is present in haemoglobin.                                                                       (6) Calcium is present in bones.            (7) Vanadium is present in cucumbers.                                                                 (8) Chromium is present in prown.  

Element which have low chemical reactivity generally occur native or free or metallic state. e.g. \[Au,\,Pt,\,\]noble gas etc. Element which are chemically reactive, generally occur in the combined state. e.g. halogens, chalcogens etc. The natural materials in which the metals occur in the earth are called minerals. The mineral from which the metal is conveniently and economically extracted is called an ore. All the ores are minerals but all  minerals cannot be ores. Ores may be divided into four groups,   (1) Metallic core (siderophile) of the earth crust contains (Mn, Fe, Co, Ni, Cu, Ru, Rb, Pd, Ag, Re, Os, Ir, Pt, Au). Entire composition of metals in earth crust may be given as,   Al (8.3%); Ca(3.6%); Na (2.8%); K (2.6%); Mg (2.1%); Ti (0.4%); Mn (0.1%); Fe (5.1%) other metals (0.1%).   (i) Native ores : These ores contain metals in free state, e.g., silver, gold, platinum, mercury, copper, etc. These are found usually associated with rock or alluvial materials like clay, sand, etc. sometimes lumps of pure metals are also found. These are termed nuggets. Iron is found in free state as meteroites which also have 20 to 30% nickel.   (ii) Sulphurised and arsenical ores : These ores consist of sulphides and arsenides in simple and complex forms of metals. Important ores of this group are    

Metal	Name of the ore	Composition
Pb	Galena	PbS
Zn	Zinc blende	ZnS
Hg	Cinnabar	HgS
Ag	Argentite or silver glance Pyrargyrite or ruby silver	\[A{{g}_{2}}S3A{{g}_{2}}S.S{{b}_{2}}{{S}_{3}}\]
Fe	Iron pyrites	\[Fe{{S}_{2}}\]
Ni	Kupfer nickel	NiAs
Cu	Copper pyrites Chalcocite or Copper glance	\[CuFe{{S}_{2}}C{{u}_{2}}S\]

  (iii) Oxidised ores : In these ores, metals are present as their oxides or oxysalts such as carbonates, nitrates, sulphates, phosphates, silicates, etc.   more...

(1) A gas may be liquefied by cooling or by the application of high pressure or by the combined effect of both. The first successful attempt for liquefying gases was made by Faraday.   (2) Gases for which the intermolecular forces of attraction are small such as \[{{H}_{2}}\], \[{{N}_{2}}\], Ar and \[{{O}_{2}}\], have low values of \[{{T}_{c}}\] and cannot be liquefied by the application of pressure are known as “permanent gases” while the gases for which the intermolecular forces of attraction are large, such as polar molecules \[N{{H}_{3}}\], \[S{{O}_{2}}\] and \[{{H}_{2}}O\] have high values of \[{{T}_{c}}\] and can be liquefied easily.   (3) Methods of liquefaction of gases : The modern methods of cooling the gas to or below their \[{{T}_{c}}\] and hence of liquefaction of gases are done by Linde's method and Claude's method.   (i) Linde's method : This process is based upon Joule-Thomson effect which states that “When a gas is allowed to expand adiabatically from a region of high pressure to a region of extremely low pressure, it is accompained by cooling.”   (ii) Claude's method : This process is based upon the principle that when a gas expands adiabatically against an external pressure (as a piston in an engine), it does some external work. Since work is done by the molecules at the cost of their kinetic energy, the temperature of the gas falls causing cooling.   (iii) By adiabatic demagnetisation.   (4) Uses of liquefied gases : Liquefied and gases compressed under a high pressure are of great importance in industries.   (i) Liquid ammonia and liquid sulphur dioxide are used as refrigerants.   (ii) Liquid carbon dioxide finds use in soda fountains.   (iii) Liquid chlorine is used for bleaching and disinfectant purposes.   (iv) Liquid air is an important source of oxygen in rockets and jet-propelled planes and bombs.   (v) Compressed oxygen is used for welding purposes.   (vi) Compressed helium is used in airships.   (5) Joule-Thomson effect : When a real gas is allowed to expand adiabatically through a porous plug or a fine hole into a region of low pressure, it is accompanied by cooling (except for hydrogen and helium which get warmed up).   Cooling takes place because some work is done to overcome the intermolecular forces of attraction. As a result, the internal energy decreases and so does the temperature.   Ideal gases do not show any cooling or heating because there are no intermolecular forces of attraction i.e., they do not show Joule-Thomson effect.   During Joule-Thomson effect, enthalpy of the system remains constant.   Joule-Thomson coefficient. \[\mu ={{(\partial T/\partial P)}_{H}}\].   For cooling, \[\mu =+ve\] (because \[dT\] and \[dP\] will be \[-ve\])   For heating \[\mu =-ve\](because \[dT=+ve,\ dP=-ve)\].   For no heating or cooling \[\mu =0\] (because \[dT=0)\].   (6) Inversion temperature : It is the temperature at which gas shows neither cooling effect nor heating effect i.e., Joule-Thomson coefficient \[\mu =0\]. Below this temperature, it shows cooling effect and above this temperature, more...

(1) Specific heat (or specific heat capacity) of a substance is the quantity of heat (in calories, joules, kcal, or kilo joules) required to raise the temperature of 1g of that substance through \[{{1}^{o}}C\]. It can be measured at constant pressure \[({{c}_{p}})\] and at constant volume \[({{c}_{v}})\].   (2) Molar heat capacity of a substance is the quantity of heat required to raise the temperature of 1 mole of the substance by \[{{1}^{o}}C\].   \[\therefore \]          Molar heat capacity = Specific heat capacity ´ Molecular weight, i.e.,   \[{{C}_{v}}={{c}_{v}}\times M\] and \[{{C}_{p}}={{c}_{p}}\times M\].   (3) Since gases upon heating show considerable tendency towards expansion if heated under constant pressure conditions, an additional energy has to be supplied for raising its temperature by \[{{1}^{o}}C\] relative to that required under constant volume conditions, i.e.,   \[{{C}_{p}}>{{C}_{v}}\]or \[{{C}_{p}}={{C}_{v}}+\text{Work done on expansion, }P\Delta V(=R)\]   where, \[{{C}_{p}}=\] molar heat capacity at constant pressure; \[{{C}_{v}}=\] molar heat capacity at constant volume.   (4) Some useful relations of Cp and Cv   (i) \[{{C}_{p}}-{{C}_{v}}=R=2\,calories=8.314J\]   (ii) \[{{C}_{v}}=\frac{3}{2}R\] (for monoatomic gas) and \[{{C}_{v}}=\frac{3}{2}+x\] (for di and polyatomic gas), where x varies from gas to gas.   (iii) \[\frac{{{C}_{p}}}{{{C}_{v}}}=\gamma \] (Ratio of molar capacities)   (iv) For monoatomic gas \[{{C}_{v}}=3\,calories\] whereas, \[{{C}_{p}}={{C}_{v}}+R=5calories\]   (v) For monoatomic gas, \[(\gamma )=\frac{{{C}_{p}}}{{{C}_{v}}}=\frac{\frac{5}{2}R}{\frac{3}{2}R}=1.66\].   (vi) For diatomic gas \[(\gamma )=\frac{{{C}_{p}}}{{{C}_{v}}}=\frac{\frac{7}{2}R}{\frac{5}{2}R}=1.40\]   (vii) For triatomic gas \[(\gamma )=\frac{{{C}_{p}}}{{{C}_{v}}}=\frac{8R}{6R}=1.33\]

(1) The motion of atoms and molecules is generally described in terms of the degree of freedom which they possess.   (2) The degrees of freedom of a molecule are defined as the independent number of parameters required to describe the state of the molecule completely.   (3) When a gaseous molecule is heated, the energy supplied to it may bring about three kinds of motion in it, these are,   (i) The translational motion      (ii) The rotational motion                    (iii) The vibrational motion.   This is expressed by saying that the molecule possesses translational, rotational and vibrational degrees of freedom.   (4) For a molecule made up of N atoms, total degrees of freedom = 3N. Further split up of these is as follows,                                                                                  Translational        Rotational         Vibrational  For linear molecule :                                           3                                 2                        3N – 5 For non-linear molecule :                                 3                                  3                       3N – 6

(1) A state for every substance at which the vapour and liquid states are indistinguishable is known as critical state. It is defined by critical temperature and critical pressure.   (2) Critical temperature \[\mathbf{(}{{\mathbf{T}}_{\mathbf{c}}}\mathbf{)}\] of a gas is that temperature above which the gas cannot be liquified however large pressure is applied. It is given by, \[{{T}_{c}}=\frac{8a}{27Rb}\]   (3) Critical pressure \[\mathbf{(}{{\mathbf{P}}_{\mathbf{c}}}\mathbf{)}\] is the minimum pressure which must be applied to a gas to liquify it at its critical temperature. It is given by, \[{{P}_{c}}=\frac{a}{27{{b}^{2}}}\]   (4) Critical volume \[\mathbf{(}{{\mathbf{V}}_{\mathbf{c}}}\mathbf{)}\] is the volume occupied by one mole of the substance at its critical temperature and critical pressure. It is given by, \[{{V}_{c}}=3b\]   (5) Critical compressibility factor \[\mathbf{(}{{\mathbf{Z}}_{\mathbf{c}}}\mathbf{)}\] is given by, \[{{Z}_{c}}=\frac{{{P}_{c}}{{V}_{c}}}{R{{T}_{c}}}=\frac{3}{8}=0.375\]   A gas behaves as a Vander Waal’s gas if its critical compressibility factor \[({{Z}_{c}})\] is equal to 0.375. A substance is the gaseous state below \[{{T}_{c}}\]is called vapour and above \[{{T}_{c}}\]is called gas.