It contains the occurrence, extraction and metallurgy, Physical and chemical properties and applications, Compounds of metals of Zirconium, Hafnium and Niobium

1. Occurrence, extraction and metallurgy
Physical and Chemical Properties and applications
Compounds of these metals, alloys and the uses:
ZIRCONIUM, HAFNIUM AND NIOBIUM

2. ZIRCONIUM
A] OCCURRENCE:
• Does not occur free in nature but is found widely distributed.
• Comprises about 0.028% of the earth's crust.
• But it is considered to be rare because it found only few concentrated sources.
• The chief sources are:
Baddeleyite ZrO2
Zircon ZrSiO4
Unlignnite Ca(Zr,Ti)2O5 Al2 TiO5
Zirkelite (Ca, Fe)O, 2(Zr, Ti, Th)O3
• The sands of Travanore (India) contain fair amounts of Zr in the form of its oxide
(ZrO2) known as Zirconia.

3. B] EXTRACTION:
Mainly extracted from its ores, Baddeleyite and Zircon.
From Zircon:
1. Zircon is best decomposed by fusion method. The pulverized zircon is fused with 4-6 times its weight of KHF.
ZrSiO4 + 8KHF2 → K2ZrF6 + K2SiF6 + H2O + 4KF
Product is extracted with hot water & then filtered to separate the insoluble K2SiF6 .
Filtrate on cooling deposits the crystals of pot. fluozirconate.
2. Pulverized zircon is fused with caustic soda or soda ash so it is converted into a mixture containing sod.
zirconate & sod. silicate.
ZrSiO4 + 4NaOH → Na2ZrO3 + 2H2O + Na2SiO3
Na2ZrO3 is converted to ZrO2 is described in case of Baddeleyite ore.
3. Finely pulverized zircon is mixed with lime & carbon. The mixture is heated to a high temp when zirconium
carbide (ZrC) is formed. The prod is then extracted with water & HCl leaving behind ZrC. It is then conveted
into ZrCl4 by treatment with Cl2 at 300℃.
ZrC + 2Cl2 → C + ZrCl4
ZrCl4 is then treated with NH4OH to yield zirconium hydroxide which on ignition is converted into ZrO2.
ZrCl4 + 4NH4OH → Zr(OH)4 + 4NH4Cl
Zr(OH)4 → 2H2O + ZrO2

4. From Baddeleyite:
1. The ore is finely powdered & then fused with 4-6 times its weight of KHF2
ZrO2 + 4KHF2 → K2ZrF6 + 2H2O + 2KF
pot.oxyfluozirconate
↓
boiled with water & the filtrate on cooling deposits the crystals.
2. Finely pulverized baddeleyite ore is fused either with caustic soda or soda ash to convert it into sod. zirconate
(Na2ZrO3). Fusion with soda ash requires higher temp than that with caustic soda.
ZrO2 + Na2CO3 → Na2ZrO3 + CO2
ZrO2 + 2NaOH → Na2ZrO3 + H2O
• The prod is sintered & extracted with water. The zirconate is hydrolysed to give insoluble hydrated oxide ZrO2.H2O.
Na2ZrO3 + 2H2O → ZrO2.H2O ↓ + 2NaOH
• The mass is extracted with HCl & the soln on evaporation yields the crystals of zirconyl chloride.
ZrO2.H2O + 2HCl → ZrOCl2 + 2H2O
• The crystals are redissolved in water & the soln of ZrOCl2, hydrated ZrO2 is precipitated by ammonia & on ignition
gives zirconium dioxide.

5. C] METALLURGY:
Pure Zr is difficult to obtain. The oxide is very stable & is not reduced by H2. Following methods are used which
produce pure metal form:
1. Redn of ZrO2 with Ca & Al:
• A mixture of zirconia & Ca is heated.
2Zr + 2Ca → CaZrO3 + 2Zr + CaO
• On raising the temp to 1050℃, cal. zirconate is further reduced to Zr.
CaZrO3 + 3Ca → Zr + 3CaO
• The prodt is cooled, powdered & washed with water, HCl, CH3COOH & again with water to remove the
impurities. Then dried at ordinary temp.
• On redn with Al, we get:
ZrO2 + 4Al → 2Al2O2 + 3Zr
2. Redn with Fluozirconate:
• Dry K2ZrF6 is mixed with potassium & then heated at low temp in an iron tube.
K2ZrF6 + 4K → 6KF + Zr
• Cold mass is washed many times with dil. HCl & a soln of NH4Cl. It is finally washed with alc to get the metal
Zr.
• Redn can also be carried out with Al but at high temp.
3K2ZrF6 + 4Al → 4AlF3 + 3Zr + 6KF
600℃

6. 3. Electrolytic Redn:
On electrolysing the soln of ZrCl4 mixed with a small proportion of FeCl2. Zr is
deposited at the cathode.
4. A very pure form of Zr metal maybe best obtained by dissociating the vapour of ZrI4
on tungsten metal filament a 1000-1500℃. But the method is costly.
ZrI4 → 2I2 + Zr
5. Redn of halides (Kroll process):
• Sublimation of ZrCl4 into molten Mg-metal where Zr is obtained by displacement.
ZrCl4 + 2Mg → 2MgCl2 + Zr
↓
removed by washing with water
• Can also be obtained by reducing with Na or Al in an evacuated iron tube
ZrCl4 + 4Na → 4NaCl + Zr
3ZrCl4 + 4Al → 4AlCl3 + 3Zr

7. D] PROPERTIES:
• Physical: Exists in 2 forms:
1. Metallic form:
 Soft,ductile, silvery white metal & forms hard alloys.
 Coherent metallic form takes a fine polish like Ni.
 Element Zr is crystalline metal.
 MP = 1857℃
 BP= 2900℃
 Sp. gr. = 6.52
2. Amorphous form:
 Bluish black powder
 Obtained by redn of K2ZrF4 or other halogen salt by Mg or an alkali metal.

8. • Chemical:
i. Rxn with water:
remains unaffected by cold water but decomposes with steam by forming ZrO2.
Zr + 2H2O → 2H2 + ZrO2
ii. Rxn with air:
Quite stable in air at ordinary temp but burns to form dioxide & some nitride at high temp.
Zr + O2 → ZrO2
2Zr + N2 → 2ZrN
iii. Rxn with hydrogen:
At about 700℃, it combines with hydrogen giving ZrH2.
iv. Rxn with metals & non-metals:
• With metals like Cu, Al, Fe, etc., forms good alloys.
• Directly combines with halogens, S, Se, Te, N, K, C, Si & B when heated to a very high
temp to form the corres. cmpds.

9. v. Rxn with alkalies:
Not attached by alkali solns at ordinary temp but when fused with alkalies in
presence of air forms alkali zirconates.
Zr + 2NaOH + O → Na2ZrO3 + H2
vi. Rxn with acids:
• Dissolves readily in HF & in aqua regia.
• Dil. H2SO4 has no action on it but hot H2SO4 (60%) reacts with it liberating SO2
• Unaffected by cold or hot dil & conc HCl & vapours of HCl attacks the metal to
form ZrCl4
Zr + 4HCl → 2H2 + ZrCl4
E] USES:
i. Refractory material:
ZrO2 is used in the manufacture of highly refractory wares & crucibles. Fire
bricks are also made with zirconia & clay.

10. ii. Glass wares:
When ZrO2 is added to glass, its resistance to chemical reagents increases
but the viscosity, density & thermal expansion decreases.
iii. Powdered form is used for ammunition, deionators & preparation of
smokeless flash-light powders.
iv. Electrical appliances:
Extensive application in photoflash bulbs, radio-transmitter tubes,
vacuum tubes, electric welding, etc.
v. Zr-alloys:
Zr-alloys are of great interest. Cu-Zr alloys have almost constant specific
resistance while tensile strength & low resistance are its distinct advantages. It
imparts to steel toughness, tenacity, resistance to wear & resistance to
corrosion. Also employed as a scavenger in the steel industries.

11. vi. Atomic reactors:
Metallic Zr is now becoming an element of outstanding interest in
the field of atomic energy because of its very slow tendency to absorb slow
neutrons. Its use is being invested.
vii. Catalyst:
Also suggested as a catalyst in hydrogenation & in synthesis of
ammonia.
F] COMPOUNDS OF Zr:
1) Halides:
Forms various halides of type ZrX4, ZrX3 & ZrX2 (X=halogen atoms).
i. Zirconium tetrafluoride, ZrF4 :
• Prepared by dissolving ZrO2 in Hf.
• Can also be prepared by the action of anhy. HF on ZrCl4.
ZrCl4 + 4HF → ZrF4 + 4HCl

12. ii. Zirconium tribromide, ZrBr3 :
• formed by passing a mixture of ZrBr4 vapours & hydrogen over an Al-wire heated to
450℃.
• ZrBr2 is also formed along ZrBr3.
iii. Zirconium triiodide, ZrI3 :
• Produced by heating ZrI4 with Zr-metal.
• In 1952, Ehrlich reported the formation of ZrF3 which decomposes to elements on being
sublimed in vacuum.
iv. Zirconium tetrachloride, ZrCl4 :
Prepared by passing Cl2 or HCl over red hot Zr
Zr + 2Cl2 → ZrCl4
Can also be prepared by passing a stream of Cl & CO over ZrO2 at 400℃
ZrO2 + 2Cl2 + 2CO → ZrCl4 + 2CO2

13. 2) Hydroxides:
Seems unable to form a true hydroxides because 2 or more hydroxyl grps in the
presence of each other on the same Zr are unstable.
3) Oxides:
Oxides of Zr : ZrO2, Zr2O2, Zr2O6, ZrO3 are known oxides.
Of all these, ZrO2 has been widely studied.

14. HAFNIUM
A] OCCURRENCE:
• Occurs in Zr-minerals, was first discovered in those minerals by X-ray method.
• occurs in extent of 0.002% in earth's crust.
• Richest minerals are Alvite which is Zirconium Thorium orthosilicate (Zr,Th,Hf)SiO4, malacone,
nageite,etc.
B] EXTRACTION:
Separation of Zirconium & Hafnium:
• Zircon contains about 0.5-2% hafnium & all extraction methods for Zr also lead to the extraction
of Hf.
• As the chemistry of these 2 metals is so similar that no direct chemical method can be employed
for their separation & independent extraction.
• The only way lies in their slight difference in extraction behavior or in their solubility of their
cmpds.
• Different methods given so far are as follows:

15. 1. Extraction of Zirconyl Chloride with Thiocynate-Rich Methyl Isobutyl Ketone (MIBK):
• Crude zirconyl chloride (ZrOCl2) is treated with counter current stream of thiocynate rich methyl
isobutyl ketone.
• Hafnyl chloride goes into the MIBK.
• Hf is preferentially extracted bbeing contaminated with less than 2% Zr.
• MIBK extract is then treated with aq.HCl & then with aq.H2SO4.
• By this treatment, Hf is brought into the aqu. layer.
• It is then ppted with NH4OH which on ignition yields oxide.
2. Fractional Crystallisation of the Double Fluorides:
• Possible to get reasonable separation by repeated crystallisation of double fluorides.
• Solubilities in water at 0℃:
(NH4)2ZrF6 : 0.611 mol/litre
(NH4)2HfF6 : 0.891 mol/litre
• In practice, the mineral is fused with pot. hydrofluoride & hexafluozirconate are separated from each
other due to difference in their solubility.
• Fractional crystallisation method is nowadays replaced by ion exchange & solvent exchange methods.

16. 3. Ion exchange method:
• Best method for separating Zr & Hf
• Mixture of (NH4)2ZrF6 & (NH4)2HfF6 is passed through an ion exchange resin of the type
[RNMe3]Cl when the hexafluoanions of Zr & Hf are absorbed by resin but at a diff. capacity
• Then the adsorbed anions are eluted with an aqu mixture of HF & HCl which releases the
hexafluoroanions from the resin.
• Anions, so formed, are eluted one after the other.
2[RNMe3]Cl + (NH4)2ZrF6 → [RNMe3]2ZrF6 + 2NH4Cl
2[RNMe3]Cl + (NH4)2HfF6 → [RNMe3]2HfF6 + 2NH4Cl
[RNMe3]2ZrF6 +2HCl → H2ZrF6 + 2[RNMe3]Cl
[RNMe3]2HfF6 + 2HCl → H2HfF6 + 2[RNMe3]Cl
4. Elution of tetrachlorides from Silica gel column:
• Anhy. methanol soln of tetrachloride of Zr & Hf is passed through silica gel column.
• Fixed chlorides are then washed first with 2N HCl in methanol which removes ZrCl4.
• Finally elution is done with 7N H2SO4 which removes HfCl4.

17. FRACTIONAL PPT METHODS:
a) Method of Caster & Haversy:
• Zirconium phosphate ZrO(H2PO4)2 & Hafnium phosphate HfO(H2PO4)2 are dissolved in HF
when the complex phosphofluozirconates & hafnates are formed.
• To this mixture, an equivalent amount of boric acid or some other born cmpd is added, when a
phosphate gets pptd which is richer in Hf than the soln from which it was originally pptd.
• By this procedure, a concn of 60% Hf can be obtained.
b) De Boer's Method:
Hf can be separated from Zr by action of water on H2SO4 soln of phosphates of 2 elements. On
dilution, Hf concentrates in the first fraction.
Fractional Volatization of Halides Van Arkel & De Boer Method:
• Hf is also separated from Zr by taking advantage of high volatility of Hf double chloride.
• It is found that HfCl4.PCl5 is more volatile than the corresp Zr cmpd (ZrCl4.PCl5) & hence
distills over earlier.
• Similarly the double fluorides can be used.

18. C] METALLURGY:
1. Redn of tetrachloride or tetraiodide:
HfCl4 + 4Na → Hf + 4NaCl
By Van Arkel & de Boer method, ie., by passing vapour of tetraiodide, HfI4 over
a heated tungsten filament, when decomposition of iodide occurs & Hf gets
deposited on filament.
HfI4 → Hf + 2I2
2. Redn of oxide:
Reduced with Na, Mg or Ca by heating strongly.
HfO2 + 2Mg → Hf + 2MgO
HfO2 + 4Na → Hf + 2Na2O
HfO2 + 2Mg → Hf + 2CaO

19. D] PROPERTIES:
• Physical:
 Like Zr, silvery white metal
 very ductile
 high MP & BP, 2200℃ & 5000℃ resp
 paramagnetic in nature
 corrosion resistant
 notable physical difference b/w Hf & Zr is their density (Zr has one-half the density of
Hf)
• Chemical:
Its chem props have been found to be similar to that of Zr
i. Rxn with acids:
Unaffected by dilute acids. However soluble in 96% of H2SO4 & is also attacked by HF.
Hf + 4HF → HfF4 + 2SO2 + 3H2O

20. ii. Rxn with oxygen:
Unaffected by air or oxygen at ordinary temp but it reacts both with oxygen & nitrogen at elevated temp.
Hf + O2 → HfO2
Hf + N2 → HfN2
iii. Rxn with halogens:
reacts with halogens at high temp forming tetrahalides. (X=halogens)
Hf + 4X → HfX4
E] USES:
• mainly used in atomic power engineering for absorbing neutrons.
• also used in electronics as cathodes of television tubes.
• largest use is as an alloying addictive (1-2%) in Ni-based super alloys. These alloys are used in turbine
vanes in combustion zone of jet aircraft engines.
• Hafnium oxide is used as an electrical insulator in microchips while Hf-catalysts have been used in
polymerisation rxns.

21. F] COMPOUNDS:
1) Oxide (Hafnium dioxide, HfO2 ):
• Also known as hafnia.
• colourless solid.
• One of the most common & stable cmpds
• reacts with strong acids & strong bases.
• dissolves slowly in HF to give fluorohafnate anions.
2) Carbide (Hafnium carbide, HfC ):
• black odourless powder.
• obtained by redn of HfO2 with carbon at 1100-2000℃
• insoluble in water.
3) Sulphide (Hafnium disulphide, HfS2 ):
• brown solid
• can be produced by reacting hydrogen sulphide and hafnium oxides at 500-1300℃
4) Sulphate (Hafnium sulphate Hf(SO4)2 ):
• obtained by dissolving hafnia in conc. H2SO4 or by action of fuming H2SO4 in HfCl4
HfO2 + 2H2SO4 → Hf(SO4)2 + 2H2O
HfCl4 + 2H2SO4 → Hf(SO4)2 + 4HCl
• white powder which decomposes at 500℃

22. NIOBIUM
A] OCCURRENCE:
• known as Columbium always occurs associated
with tantalum in nature.
• A no. of ores have been discovered out of which
the important ones are as follows:
1. Pyrochlore:
• complex of Na & Ca with general compositon as
(Na.Ca.Nb2O6.F)
• contains about 55% Nb2O5 & 4% Ta2O5
2. Euxenite:
• complex niobate titanite of Y, Ce, Er, Th, Zr &
U
• possesses 18-35% of Nb2O5
3. Fergusonite:
• metaniobate & tantalate with composition
(Y,Er,Ce)(Nb,Ta)O4
4. Columbite:
• General formula: (Fe,Mn)(Nb,Ta)2O6
• contains 26-77% Nb2O5 & 1-77% Ta2O5
5. Tantalite:
• same general composition of columbite
• may have 3-40% Nb2O5 & 42-84% Ta2O5

23. B] EXTRACTION:
• main sources for niobium or tantalum is the mineral niobite
• extraction for both the metals are similar & hence these 2 metals are extracted
together freed from other elements & then separated from each other
• Methods followed for extraction of metals are only fusion methods since their
cmpds are insoluble in mineral acids except HF:
a] Fusion with KHSO4 :
• Ore niobite is finely powdered & fused with 7 parts of pot.hydrogen sulphate in
iron vessel
• fused mass is extracted with boiling water when Fe, Mn, etc form their sulphates &
pass into the soln. Sn & W, if any are then separated by digesting the residue with
yellow (NH4)2S.
• the residue containing oxide of Nb, Ta & Si is washed with water & treated with
HF when most of SiO2 is removed as silicon tetrafluoride vapours.
• enough amount of KF is then added to get K2NbOF5 & K2TaF7.

24. 2Fe(NbO3)2 + 4KHSO4 → 2FeSO4 + 2Nb2O5 + 2H2O + 2K2SO4
Nb2O5 +10HF → 2NbF5 + 5H2O
NbF5 +2KF + H2O → K2NbPF5 + 2HF
Fe(TaO3)2 + KHSO4 → 2FeSO4 + 2Ta2O5 + 2H2O + 2K2SO4
Ta2O5 + 10HF → 2TaF5 + 5H2O
TaF5 + 2KF → K2TaF7
• since the solubility of K2NbO5 is 10 times more than that of K2TaF7, most of the Ta-salt
is separated out by fractional crystallisation from Nb-salt as neddle shaped crystal.
b] Fusion with caustic soda:
• Ore niobite is finely powdered & then fused with NaOH
Fe(NbO3)2 + 2NaOH → 2NaNbO5 + H2O + FeO
sod. niobate
Fe(TaO3)2 + 2NaOH → 2NaTaO3 + H2O + FeO
sod. tantalate

25. • fused mass-extracted with dil. HCl & the residue-digested with conc. HCl
• acid solns- mixed together which on concn yields hydrated Nb2O5 & Ta2O5 as white powder
Fe(NbO3)2 + 2HCl → FeCl2 + 2HNbO3
2HNbO3 → Nb2O5 ↓ + H2O
2NaNbO3 + 2HCl → 2NaCl + Nb2O5 ↓ + H2O
2NaTaO2 + 2HCl → 2NaCl + Ta2O5 + H2O
• white powder is washed with water & then dissolved in HCl & then large amounts of KF is
added to the soln to obtain pot. niobium oxyfluoride (K2NbOF5) & pot. tantalum fluoride
(K2TaF7)
Nb2O5 + 10HF → 2NbF5 + 5H2O
NbF5 + 2KF + H2O → K2NbOF5 + 2HF
Ta2O5 + 10HF → 2TaF5 + 5H2O
TaF5 + 2KF → K2TaF7
• Chakravarthy & Prince (1957) : above process is effective in case of Pyrochlore mineral also
which fails to respond to other conventional methods.
• Ta- salt K2TaF7 separated from soln by fractional crystallisation.
• It can also be done by Separating Ta & Nb (K2TaF7 & K2NbOF5.H2O) by Fractional
crystallisation where end prodts are K2TaF7 & Nb2O5 .

26. C] METALLURGY:
1. Kroll's method:
• NbCl5 is sublimated over Mg in a glass tube at 750℃ in atmosphere of He.
• After completion of rxn, MgCl2 removed by distilling in vacuum at 900℃.
2. Sod. redn of chloride:
• Molten NbCl5 is brought in contact with molten NaCl.
• redn takes place & Nb-metal granules sink to bottom.
3. Alumino thermic redn of pentoxide:
• Pure Nb2O5 & Al is heated strongly to form an alloy from which Al can be voltalized during prolonged fusion in electric
vacuum furnance.
4. Carbide redn of pentoxide:
• Mixture of NbC & Nb2O5 is heated to a temp 1800℃ in vacuum, redn of pentoxide into metal takes place & CO is evolved.
However, some oxide is voltalized as such causing loss of yield.
Purification of metal:
Van Arkel & De Boer's method:
• Impure metal & little niobium iodide is taken in an evacuated vessel through the centre of which runs a thin wire of very
pure Nb which is heated to a very high temp., while the temp of the vessel is kept lower.
• Iodide decomposes on the wire depositing the metal on it & releasing iodide which combines with impure metal.
• This cycle continues tii the wire becomes sufficiently thick & then it is taken out.

27. D] PROPERTIES:
• Physical:
 steel grey metal
 bright characteristic lustre & a slight yellow tinge.
 MP= 1450℃
 BP= 3700℃
 Sp. gravity= 8.5
• Chemical:
 very reactive & resists attacks of many chemmical reagents.
 difficult to obtain in pure state because at high temp it reacts with oxygen & nitrogen.
i. Rxn with nitrogen:
Nitrogen at 1200℃ combines with Nb to form nitride.
ii. Rxn with hydrogen:
Nb is heated in H2 to form NbH.

28. iii. Rxn with water:
Unaffected by water but decomposes at red heat liberating hydrogen.
iv. Rxn with air:
• stable in air at ordinary temp.
• But on heating forms a protective film of its oxide.
v. Rxn with halogen:
metal burns with incandescence in fluorine at RT but speedily with chlorine when heated
to redness.
2Nb + 3F2 → 2NbF3
2Nb +5Cl2 → 2NbCl5
vi. Rxn with alkalies:
does not dissolve in soln of caustic alkalies but when fused with caustic soda, it forms
alkali metal Nb.
vii. Rxn with acids:
• dissolves slowly in HF to form trifluoride.
• not dissolved by HCl, HNO3 & aqua regia.

29. E] USES:
• Pure Nb is used in jet engines & rocket missiles.
• In construction of nuclear reactor because of its negligible tendency to absorb thermal neutrons & excellent high
temp mechanical props.
• as an alloying agent: increases the strength of low carbon steels at high temp & minimizes intergranular corrosion.
• used in arc wielding rods for some stabilized grades of stainless steel.
F] COMPOUNDS:
• Nb is pentavalent in most of its cmpds but it is trivalent in some of its cmpds.
• There is also tendency to form oxycmpds.
1) Halide :
Niobium pentachloride (NbCl5 ):
• Nb is heated in Cl2 or pentoxide is heated with CCl4
2Nb + 5Cl2 → 2NbCl5
Nb2O5 + 5CCl4 → 2NbCl5 + 5COCl2
• yellow crystalline solid
• dissolves in many org solvents
• decomposed by water forming hydrated pentoxide

30. 2) Oxide :
Niobium pentaoxide (Nb2O5 ) :
• obtained by heating the element, its sulphide, carbide or nitride in air.
• more conveniently prepared by heating sod. or pot. niobates with an acid.
• ppt is hydrated oxide which on heating gives the pentaoxide.
2KNbO3 + 2HCl → Nb2O5 + H2O + 2KCl
Nb2O5.H2O → Nb2O5 + H2O ↑
• When obtained by pptn method, it is white amorphous powder but if heated to red heat becomes incandescent & passes
into crystalline state.
• insoluble in water & amphoteric but acidic character is prominnt.
• dissolves in fused KOH or KHSO4.
3) Nitride :
Niobium nitride (NbN):
• obtained by heating Nb with nitrogen at 1200℃
• grey metallic, interstitial cmpd
• On strong heating in air, converts in Nb2O5.
• Nb also forms Nb2N2.

31. BIBLIOGRAPHY:
www.google.com
 www.wikipedia.org
 Priniples of Inorganic Chemistry; Puri, Sharma and Kalia
 Industrial Chemistry; B.K.Sharma