Introduction to Zinc
By Anup Pokhrel
|Discovery date||The element was discovered as an element in 1746, but known to the Greeks and Romans before 20BC.|
|Origin of the name||derivation of the name was from the German word, ‘zinc’.|
|Group||12||Melting point||419.527°C, 787.149°F, 692.677 K|
|Period||4||Boiling point||907°C, 1665°F, 1180 K|
|Block||d||Density||7.134 gram per centimeter|
|State at 20 °C||liquid||Key isotope||64Zn|
|Atomic number||30||Atomic mass||65.38|
The compounds of zinc are:
The term hydride is used to indicate compounds of the type MxHy and it is not necessarily that indicated any compounds listed would behave as same as hydrides chemically.
- Zinc hydride: ZnH2
- Zinc difluoride: ZnF2
- Zinc dichloride: ZnCl2
- Zinc dibromides: ZnBr2
- Zinc diiodide: ZnI2
- Zinc oxide: ZnO
- Zinc peroxide: ZnO2
- Zinc sulphide: ZnS
- Zinc selenide: ZnSe
- Zinc telluride: ZnTe
- Trizinc dinitride: Zn3N2
- Hexaaquozinc dinitrate: Zn(NO3)2.6H2O
- Zinc sulphate pentahydrate: ZnSO4.7H2O
Calamine → ZnCO3
Zincite → ZnO
Zinc blende → ZnS
Willemite → ZnO.SiO2
Extraction of zinc (Zn)
It is extracted from ZnS.
- Concentration: at first the ore is crushed into fine pieces and then powdered into the ball mills. The concentrated ore is then subjected to froth flotation method.
- Roasting: The concentrated ore is roasted in the presence of air at about 900 where zinc sulphide is turned to zinc oxide.
During the process, the impurities like arsenic, phosphorus, sulphur etc. are expelled out in the form of volatile oxide.
- Vertical retord processing: The obtained zinc oxide is mixed with coke dust in the ratio 2:1 then the small briquettes are made from it. These briquettes are put into vertical retord.
When the furnace is heated by burning to about 1400, the oxide ores in briquettes gets reduced and vapors of zinc and carbon monoxide are formed and carried to the condenser. The vapors of zinc condense in the condenser in the form of molten mass called zinc splinter.
- Fractional distillation: At first, zinc splinter is distilled over 1000 where zinc and Cd distil over leaving behind the impurities. The impure zinc is then distilled leaving behind the zinc.
- Electrolysis: In this method impure zinc is taken as the anode and pure zinc as the cathode. When the electric current is passed over, impure zinc from anode dissolve out and pure zinc is deposited at the cathode.
Zn – 2e– → Zn2+
Zn2+ + 2e– → Zn
- It is bluish white shining metal.
- It is a good conductor of heat and electricity.
- It is malleable and ductile.
- Action with air: when zinc reacts with moist air, it forms basic carbonate of zinc.
- Action with water: zinc reacts with water to form zinc hydroxide and hydrogen gas.
- Action with heat: zinc when heated in the presence of air, it burns with the greenish-blue flame of zinc oxide. It is also known as philosopher’s wool.
- Action with NaOH: On boiling with the alkali solution (NaOH) it evolved out hydrogen gas.
- Action with metal salt: It displaces less electropositive metals from their salt.
- Reaction with acid
Uses of Zinc
- Mostly zinc is used to galvanize other metals in order to prevent them from rusting. Galvanized steel is used for car bodies, street lamp posts suspension bridges etc..
- Large quantities of zinc are used to produce metals by pouring molten metal into a mold, which is widely used in the automobile, electrical and hardware industries. Zinc is also used in alloys such as brass, nickel silver, and aluminium solder.
- Zinc oxide is used in the manufacture of many products such as paints, rubber, cosmetics, pharmaceuticals electrical equipment etc. Zinc sulfide is used in making luminous paints, fluorescent lights and x-ray screens.
Zinc is found in several ores in the form of zinc blende and calamine. The principal mining areas are in China, Australia, and Peru. Commercially, zinc is obtained from its ores by concentrating and roasting the ore, then reducing it to zinc by heating with carbon or by electrolysis. World production is more than 11 million tons a year.