INORGANIC CHEMISTRY

ORES, MINERALSANDEXTRACTIVEMETALLURGY
Ores and minerals Commonlyoccurring oresofiron, copper, lead, magnesiumand aluminium.
(Mains Only : Tin and silver)
Extractivemetallurgy (Chemicalprinciplesand reactions only;industrialdetails excluded):
Carbon reduction method (iron)(Mains Only : Tin also),
Selfreduction method(copper and lead),
Electrolyticreductionmethod(magnesiumand aluminium),
(Mains Only : cyanide process :Gold and silver)
ORES AND MINERALS
Metals occur in nature in combined formasminerals.
Minerals fromwhich a metalcan be profitably extracted is termed asore. e.g. FeS2 is a mineralof
iron, not anore.
IMPORTANT ORES OFSOME METALS (Principal ore is given in bold letters)
Iron: In the combinedstate, iron occurs inthe following minerals.
Haematite, Fe2O3 Magnetite, Fe3O4
Limonite, 3Fe2O3 · 3H2O Spathic iron ore, FeCO3
Tin: Cassiterite or tin stone, SnO2.
Copper occurs inthe native state as wellas in the compounds form. The naturalores of
copper are
Copper pyrites, CuFeS2 Malachite, Cu(OH)2 · CuCO3(green)
Cuprite or ruby copper, Cu2O Azurite, Cu(OH)2·2CuCO3
Copper glance, Cu2S Cu5FeS4(peacock ore)
Lead:
Galena, PbS Cerussite, PbCO3
Anglesite, PbSO4 Wulfenite, PbMnO4
Stolzite, PbWO4
Magnesium :
Dolomite, MgCO3 · CaCO3 Carnallite, MgCl2·KCl·6H2O
Magnesite, MgCO3 Epsomite(epsomsalt), 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
occurs in minerallike olivine (Mg2SiO4), spinel (MgAl2O4),
talc (Mg3H2(SiO3)4), asbestos (CaMg3(SiO3)4), etc.
Aluminium: Aluminiumisthethird most abundant element ofearth’s crust.
Oxides: Corundum, Al2O3; diaspore, Al2O3·H2O and bauxite, Al2O3·2H2O.
Fluorides: Cryolite, Na3AlF6
Silicates: Feldspar, KAlSiO3O8, mica(KAlSi3O10(OH)2) and
kaolinite (Al(OH)4, Si2O5)
Basic Sulphates: Alunite or alumstone, K2SO4·Al2(SO4)3·2Al(OH)3
Basic Phosphates: Turquoise,AlPO4·Al(OH)3·H2O
Aluminates: Aluminates ofMg, Fe and Mn.
Silver in the native formis associated with copper and gold. The main ores ofsilver are
Argentite or silver glance, Ag2S Hornsilver,AgCl
Proustite, 3Ag2S ·As2S3 Pyragyrite, 3Ag2S · Sb2S3

METALLURGICALPROCESSES
INITIAL TREATMENT
(i) Crushing and Grinding :The oreis first crushed byjaw crushers and ground invarioussize reduction
equipments likeballmills.
(ii) Concentration (dressing) of Ore: The crushed ore is concentrated either by one of the following
methods orbytheir combination.
(a) Gravity Separation:When the differencein densities oforeand gangue is considerable, the ore canbe
concentrated bya streamofrunning waterwhichwashes offthelighter gangue particles.
(b) Magnetic Separation Anyore having magnetic properties can effectively be separated by magnetic
separation. e.g.
(c) Froth Floatation: Mostlyemployed for sulphide ores. Water is mixed with3.5% byweight eucalyptus oil
(or some other cheap oil) and the mixture is stirred by compressed air as shown in Fig.2. Froth is
generated at surface. Sulphide particles inores are preferentiallywettedbythis frothandrise to surface.
Theyare skimmed offbya skimmer. Gangue is preferentiallywetted bywater and it sinks to bottom.
Reagents employedin frothfloatationare offour types.
(I) FROTHERS: Which create frothe.g. palmoil.
(II) COLLECTORS: Whichhelp in attachment ofore particle to anair bubble in forth. e.g. Sodiumxanthates
(III)ACTIVATORS: Simpleinorganic compounds whichenhanceoffloating propertyofmetalsulphide e.g.CuSO4
(IV) DEPRESSANTS: Which suppress the floatationofa particular particleselectively, e.g. when anore containing
PbS and ZnS is floated in presence ofCN-, floatation of ZnS is suppressed and onlyPbS is
removed. CN- is thendestroyed byanyoxidizing agent and ZnS is floated again.
Calcination. When the ore is heated below its melting point inlimited supplyof air, chiefly decomposition
reactionsoccur. Thisis roasting. It is highlyendothermic. During calcination:
* Allthe volatileimpuritiesare lost
* Water ofcrystallizations is lost
Al2O3 · 2H2O  Al2O3 + 2H2O(g) 
Roasting is done at a temperatureslightlyhigher thanthat ofcalcination inexcess ofair. The ore doesnot melt
during roasting. All the combustible organic matter burns away and the ore becomes more porous.
Exothermic reactions supplymuch ofthe heat and much lesser energyis required inthis case.
Sintering: Heatingtillfusionoforejust begins. Helps inconverting smallplaces ofore to a biggermass. Most of
the features arecommonwith roasting.
FURNACES. Furnaces areeither powered byfuel(mostlycoal, as inblast furnace or reverberatoryfurnace) or
byelectricity.Fuelfiredfurnaces generatormaximumtemperatureof1400-1500°Cwhileelectricfurnaces
can supplyas high as 3000° temperature.
Fig.1
MAGNETIC SEPARATION
ORE
NON-
MAGNETIC
PARTICLES
MAGNETIC
PARTICLES
 
ELECTRO-
MAGNETIC
WHEEL 

FROTH FLOATATION
COMPRESSED AIR
OIL
WATER
MIXTURE





FROTH
SKIMMER
CONCENTRATED
ORE
GANGUE
Fig.2

Kilns. When fueland ore are mixed and heated. No reduction occurs. e.g. Lime Kilns.
Blast Furnace.Fuel and ore are mixed and charged fromthe top offurnace andhot air is blownfromthe holes
(tuyers) near the bottom. The ore is reduced as it descends down.
Reverberatory Furnace.Materialto be heated is placed on the hearth ofa reverberatoryfurnace.As hot air is
blown in(see fig.) flames rise and hit the concavetop ofthe furnace, therebyturning in andheating the
hearth. fueland ore are separate in this case.
GENERALCLASSIFICATION OFEXTRACTION PROCESSES
An ore to be treated must first be examined. Following methods should be tried (inthis sequence).
Mechanical Separation Ifmetal occurs in its native state(e.g. gold), it is simplyseparated mechanicallyby
crushing thenuggets or rocks andseparating it.
ThermalDecomposition:Ifaparticularcompoundcansimplydecomposeonheatingthenthemetalisrecovered
bysimple heating. e.g. Hg fromHgO. Two interesting processes are described below.
(i) Mond’s Process. When nickel oxide is heated with water gas (CO + H2), H2 reduces nickel oxide to
nickel, whichreadilycombines with CO to formNi(CO)4 , a highlyinflammable, volatilegas. This gas,
when separated out and heated to 180°C, decomposes to give pure nickel.
(ii) vanArkel’s Process. Manymetals (e.g. zirconium) formvolatile iodides which, whencontacted with
hot tungstenwire, release I2 andthe metalis depositedonthewire. Whensufficient quantityofmetalhas
beendeposited, tungsten core is bored out. This method is used for obtaining smallquantities ofhighly
puremetal.
DisplacementMethod:Inthismethodacheapermetal, whichoccupiesahigherplaceinelectrochemical
series, displaces a costlier metal fromits salt solution. e.g. displacement of gold and silver fromtheir
solutionbyscrap zinc incyanideprocess.Another example istreatment ofleanoreofcopper (containing
very small amount ofcopper). Such ores are dug out and dumped in trenches inopen. The rainwater
collects in trenches and dissolves the sulphides when they are oxidised to sulphates by atmospheric
oxygen.
CuS + 2O2 CuSO4 (aq)
After a year or two, dilute solutionofcopper sulphate is simplypumped out leaving behind allthemud
and otherimpurities. This solution, whentreated withscrap iron, precipitates copper.
Cu2+ (aq) + Fe Fe2+ (aq) + Cu
High Temperature Chemical Reduction.
(i) By Carbon. e.g. inmetallurgyofironand tin (discussed later).
(ii) Thermite Process : Reduction byaluminium is highly exothermic, so much so that the products are
formed in molten state. This is thermite process. e.g. Cr2O3 + 2AlAl2O3 + 2Cr + heat
(iii) Self Reduction as in the case od copper and lead (discussed later).
ELECTROLYTIC REDUCTION
(i) Inaqueoussolutionand
(ii) In fusedmelts, ifthe metalis too reactive. It is costly, hence it is resorted to onlywhenno other method
is available. e.g. for Na, Mg,Aletc. (discussed later).
Fig. 3
 CHIMNEY
AIR
ASHES
HEARTH




EXTRACTIVE METALLURGY
IRON AND TIN
Both iron and tin are extracted by the carbon reduction method.
Extraction of Iron
Iron is extracted from its principal ore, haematite. After the preliminarywashing, concentration and
roasting, the ore is smelted in the presence of coke and limestone in a blast furnace (fig.1).
Roasted ore (8 parts) with desulphurized coke (4 parts) and limestone pieces (1 part) is fed into
the blast furnace from the top. Preheated air is blown in through waterjacketed pipes called
tuyeres fixed in the lower part ofthe furnace. There is a temperature gradient as we move from the
bottom (temperature about 2000K) to the top (temperature about 500K) of the blast furnace. The
blast furnace maybe broadly divided into three main parts as described in the following.
1. Zinc of fusion The lower portion where coke burns and produced carbon dioxide and a lot of
heating is known as zone of fusion:
C + O2  CO2 H = 406 kJ mol1
Here the temperature is about 1775 K. Alittle above this, where temperature is above this, where
temperature is about 1475 K  1575 K, iron coming from above melts.
2. Zone of heat absorption The middle portion (temperature 1075 K  1275 K), CO2 rising up
is reduced to CO with the absorption of heat:
CO2 + C  2CO H = 163 kJ mol1
In this portion, limestone coming from above is decomposed and the resultant lime (CaO), which
acts as flux, combines with silica (present as impuritygangue) to form calcium silicate (fusible
slag): CaCO3  CaO + CO2
CaO + SiO2  CaSiO3
3. Zone of reduction The upper portion (675K 975K) where iron oxide is reduced to spongy
iron bycarbon monoxide rising up the furnace:
Fe2O3 + 3CO  2Fe + 3CO2
Fig.4
BLAST FURNACE
WASTE GASES
FIRE BRICKS
HOT AIR BLAST
SLAG
1500K
1800K
2000K
I RO N
HEARTH
500K
1000K
CHARGE (ORE, LIMESTONE AND COKE)
G
AS
E
S
R
I
S
E
C+ O2
 C O2
SOLID
CHARGE
DESCENDS
3Fe2
O3
+ CO  2Fe3
O4
- CO2
CaCO3
 CaO + CO2
Fe3
O4
+ CO  3FeO + CO2
Phosphates and Silicates reduced,
Impure iron melts
C+CO2
 2CO
FeO + CO  Fe(S) + CO2
P and S pass into molten iron
Molten slag forms

The reduction is believed to take place in stages:
3Fe2O3 + CO  2Fe3O4 + CO2
Fe3O4 + CO  3FeO + CO2
FeO + CO  Fe + CO2
At the bottom of the furnace the molten iron sinks down while above this floats the fusible slag
which protects the molten iron form oxidation. These two can be removed from different holes
(Fig. 4). Waste gases escaping at the top consists of about 30% CO, 10% CO2 and the rest
nitrogen.
Iron obtained from the blast furnace is known as pig iron.
Pig iron contains about 25% carbon as well as other impurities (usually Si, Mn, S and P). Pig iron
is converted into cast iron by remelting in a vertical furnace heated by coke. Cast iron expands on
solidification and is used for casting various articles. Wrought iron, which is the purest form of iron,
can be obtained by heating cast iron in a reverberatoryfurnace lined with iron oxide. Wrought iron
contains about 0.2% carbon.
Extraction of Tin.
Metallic tin is extracted from tin stone which contains about 10% of the metal as SnO2 , the rest
being siliceous matter, tungstates of Fe, Cu and As.
After crushing, the ore is concentrated by washing in a current ofwater (Gravityprocess to remove
lighter gangue particles) and by magnetic separator to remove tungstates of Fe and Mn.
The ore is roasted to remove A and As their oxides. The ore then may be washed to remove
sulphates of Cu and Fe. This gives black tin.
Finally, the ore is smelted in a reverberatoryfurnace or in a blast furnace at 14751575K. The ore
is mixed with onefifth ofits mass of powdered anthracite (coal) and little of lime or fluorspar which
is used as flux. Tin oxide is reduced to tin:
SnO2 + 2C  Sn + 2CO
The molten metal collected from the bottom of furnace contains impurities such as Fe, Pb, S and
As. The metalmay be purified electrolytically
REFINING OF TIN
(i) Liquation or sweating- When the block of impure tin is heated on the sloping hearth of
reverberatory furnace tin, alongwith lead and bismuth (all having a much lower melting points than
other metals), run off leaving dross, an alloy of Sn, Fe, Cu, W, As.
(ii) Poling (stirring with logs of green wood) of this sweated tin is done. Impurities get oxidised &
form scum which is skimmed off. 99% Sn is obtained.
Scum & dross are repurified. Slag contains 1025% Sn as SnSiO3 because of amphoteric nature
of tin. This is recovered by smelting with carbon and CaO flux at a much higher temperature.
SnSiO3 + CaO + C  Sn + CaSiO3 + CO
Electrolytic refining : Cathodepure metal, Anode pure tin, Electrolyte SnSO4(aq) with sulphuric
acid and hydrofluosilicic acid.
COPPER AND LEAD
Both copper and lead may be extracted by selfreduction method.
Extraction of Copper :Copper is mainly extracted fromcopper pyrites. After the concentration of
its ore byfroth flotation process, the ore is roasted in a current of air to remove arsenic, antimony
and much of sulphur. The reactions occurring are
(i) 2CuFeS2 + O2  Cu2S + 2FeS + SO2  (major reaction)
(ii) 2Cu2S + 3O2  2Cu2O + 2SO2
(iii) 2FeS + 3O2  2FeO + 2SO2 (minor reactions)

The ore is then mixed with a little coke and sand and smelted in a waterjacketed blast furnace.
The minor reactions that occured during roasting continue here. Ferrous oxide combines with sand
to forma fusible slag. 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.
(iv) FeO + SiO2  FeSiO3
(v) Cu2 O + 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 Bessemer converter (Fig. 5). Ablast 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 oxides and ferrous oxide as slag (reaction iv). At the same time Cu2S is
oxidized mostly into Cu2O (reaction ii) and partly into CuO and CuSO4. Allthese react with Cu2S
giving copper. The reactions are
(ii) 2Cu2S + 3O2  2Cu2O + 2SO2 
2Cu2S + 5O2  2CuSO4 + 2CuO
2Cu2O + Cu2S  6Cu + SO2 
CuSO4 + Cu2S  3Cu + 2SO2 
Cu2S + 2 CuO  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 flotation process, the ore is roasted in a reverberatory furnace for about six hours at a
moderate temperature in a current of air. Part of galena is converted into lead oxide and lead
sulphate. After this, the supply of air is stopped and small quantities of carbon, quicklime and
cheap iron ore are added along with increase of temperature. At this stage, unreacted sulphide
reacts with the lead oxide and sulphate giving metallic lead:
PbS + 2PbO  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 moltenzinc is added to molten impure lead. The former is immiscible with the latter.
Silver is more soluble in molten zinc than in molten lead. Zincsilver alloy solidifies earlier then
molten lead and thus can be separated.After this, crude lead is refined electrolytically (Electrolyte;
lead silicofluoride, PbSiF6 and hydrofluosilicic acid, H2SiF6 with a little gelatin, anode; crude lead
and cathode; pure lead).
Converter 
SiO2
-- air 
Molten matte
FIG. 5
BESSEMER CONVERTER

MAGNESIUM AND ALUMINIUM
Extraction of magnesium Magnesium is commonly obtained by the electrolysis of fused
magnesium chloride containing a little (25%) sodium chloride and sodium fluoride at 7000C 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 then the electrolyte, it floats
over the fused electrolyte and is withdrawn (Fig. 6). Voltage ~ 6V.
In Dow process, magnesium is recovered from seawater as magnesium chloride which is then
electrolysed using cell described above (Fig. 6).
Dow’s Sea Water Process. Sea water contains 0.13% Mg ions.
Mg2+ (seawater) + Ca(OH)2 (fromoyster shells)  Mg(OH)2 + CaCl2 MgCl2
.2H2O
MgCl2
.2H2O   MgCl2
.1.5H2O   MgCl2
Dow’s Natural Brine Process.
MgCO3.CaCO3  MgO.CaO  CaCl2 (aq)+ MgCl2(aq)  MgCl2(aq) + CaCO3
(dolomite) (calcineddolomite)
The reaction is : CaCl2
.MgCl2(aq) MgO.CaO + 2CO2  MgCl2(aq) + 2CaCO3 3
Electrolysis. 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 thecathode dissolves inmoltenlead. Thealloyofleadmagnesiumissubjectedto electrolysis
to obtainpure magnesium(electrolyte: fusedcarnallite, anodeleadmagnesiumalloyandcathodesteel
rods.)
Extraction ofAluminiumAluminiumis isolatedfromthe electrolysis ofbauxite,Al2O3· 2H2O. Since it
is difficult to purifyaluminium, bauxite ore is purified either byBaeyer's process (or Hall's process) or
Serpek's process depending upon the impuritypresent in the ore.
Ifthe bauxite contains iron oxide as the impurity, one can use Baeyer's or Hall's process as described
below.
FIG. 6
ELECTROLYTIC CELL FOR THE
PRODUCTION OF MAGNESIUM
Graphite anode
Porcelain hood
Inert gas
(coal gas)
Iron cathode
Mg
Molten electrolyte
Cl2
Inert gas
Iron cell
Thickened in
Dorr Thickeners
dil. HCl (10%)
spray drying
dry HCl
heat
dil. HCl
heat CO2
( c a lc in ed
dolomite)

Baeyer's Process: Finallygroundoreis roasted to convertferrousoxide to ferricoxideand thendigested
with concentrated caustic soda solution at 423K.Al2O3 dissolves while Fe2O3 remains undissolved.
The latter is filtered offand fromthe solutionAl(OH)3 givesAl2O3.
Al2O3 + 2OH + 3H2O  2Al(OH)
4
Aluminate ion dissolves
Al(OH)
4 + H+  Al(OH)3 + H2O
precipitates
2Al(OH)3
heat
 
 Al2O3 + 3H2O
Hall's Process: In this process the ore is fused with sodium carbonate when soluble metaaluminate
(NaAlO2) isproduced. This is extractedwithwater leaving behind iron oxide. Carbondioxide at 323
333 K is passed throughwater extract to getAl(OH)3 whichon heating givesAl2O3.
Al2O3 + Na2CO3
fused
 

 2NaAlO2 + CO2
extracted withwater
2NaAlO2 + 3H2O + CO2  2Al(OH)3 + Na2CO3
2Al(OH)3
heat
 
 Al2 O3 + 3H2O
Ifthe impurityis silica, the Serpek's process is used to purifybauxite.
Serpek's Process : The powdered ore is mixed with coke and heated to 2075K in a current of
nitrogen. Silicapresent isreduced to siliconwhichvolatilizes offandaluminagivesaluminiumnitride. The
hydrolysis ofthelatter givesAl(OH)3, heating ofwhichgivesAl2O3.
SiO2 + 2C  Si ­ + 2CO2­
Al2O3 + 3C + N2  2AlN + 3CO
AlN + 3H2O  Al(OH)3 + NH3
2Al(OH)3 heat
 
 Al2O3 + 3H2O
After obtaining pureAl2O3, it is dissolved in fused cryollite, Na3AlF6, withalittle fluorspar, CaF2 and is
electrolysed in anirontank lined withblocks ofcarbonwhichserve as the cathode. The anode consists
ofa number ofgraphite rods suspended verticallyinside the tank (Fig. 7)
Aluminiumgets settled at the bottomofthe tank and can be removed. The reactions occurring at the
electrodes are
Cathode Al3+ + 3e  Al
Anode 2O2
2  O2 + 4e
C + O2  CO2
Anode isreplaced periodicallybecause ofits consumption.
SILVERAND GOLD
Cyanide Process: Silver and gold are extracted bythe cyanide process (MacArthurForrest process).
After the preliminarycrushing and concentrationbyfrothfloatationprocess, theore (crushed auriferous
rocks in the case ofgold)is leached with dilute (0.47%) solutionofsodiumcyanide made alkaline by
adding lime kept agitated bya current ofair. Silver (or gold) pass into solutionas argentocyanide(or
aurocyanide) :
Ag2S + 4NaCN l 2Na[Ag(CN)2] + Na2S
FIG. 7
ELECTROLYTIC CELLFORTHE PRODUCTION OF
ALUMINIUM
At the cathode : Al3+
+ 3e-
 Al
At the anode: C(s) + 2O2-
 CO2
(g) + 4e-

The air blown in remove Na2S as Na2S2O3 and Na2SO4 causing the above reaction to proceed to
completion.
2Na2S + 2O2 + H2O  Na2S2O3 + 2NaOH
Na2S2O3 + 2NaOH + 2O2  2Na2SO4 + H2O
4Au + 8NaCN + 2H2O + O2 l 4Na[Au(CN)2] + 4NaOH
The solution obtained above is filtered and treated with scrap iron or zinc when silver (or gold) get
precipitated:
2Ag(CN)
2 + Zn  Zn(CN)2
4 + 2Ag
2Na[Au(CN)2] + Zn  Na2[Zn(CN)4] + 2Au
Theobtainedsilver ispurified electrolytically(electrolyte:silvernitrate solutioncontaining1%nitric acid,
anode: impuresilver and cathode: puresilver). The impurities likezinc and copper passinto the solution
while gold fallsdown as anode mud.
Gold thus obtained is contaminated by zinc which is dissolved out by sulphuric acid. The dried
residue of gold is then fused under borax (flux) in graphite crucible and the melted down gold
(bullion) which invariably contains silver, is sent for refining.
METALLURGY AT A GLANCE