Availability: Zinc is available in many forms including dust, foil, granules, powder, pieces, nanosize activated powder, shot, and a mossy form.
Who: Andreas Marggraf
German: zin (German for tin). “Zinc” in different languages.
Found in the minerals zinc blende (sphalerite) (ZnS), calamine (ZnO), franklinite ((Fe,Mn,Zn)(Fe,Mn)2O4), smithsonite (ZnCO3), willemite (Zn2SiO4), and zincite (ZnO). The largest producers are Australia, Canada, Peru and the USA. Annual production is around 5 million tons.
Seawater: Atlantic surface: 5 x 10-5 ppm; Atlantic deep: 1 x 10-4 ppm; Pacific surface: 5 x 10-5 ppm; Pacific deep: 5.2 x 10-4 ppm
Human: 33000 ppb by weight; 3200 ppb by atoms
Used to coat other metals (galvanizing) to protect them from rusting. Used in alloys such as brass, bronze, nickel. Also in solder, cosmetics and pigments.
Zinc Oxide is used as a white pigment in watercolours and paints. It can also be found as an over-the-counter ointment that is appplied to the exposed skin of the face or nose to prevent dehydration. It can also prevent sunburn.
Zinc Chloride (ZnCl2) is used as a deodorant and can also be used as wood preservative.
Zinc Sulfide (ZnS) is used in luminescent pigments such as those on the hands of clocks and other items that glow in the dark.
Calamine lotion, used to treat skin rashes, is a mix of Zn-(hydroxy-)carbonates and silicates.
Throat lozenges, used as remedies for the common cold, use Zinc Gluconate Glycine (C12H22O14Zn) and Zinc acetate.
In ancient India the production of zinc metal was very common. Many mine sites of Zawarmaala were active even during 1300-1000 BC. There are references of medicinal uses of zinc in the Charaka Samhita (300 BC). The Rasaratna Samuccaya (800 AD) explains the existence of two types of ores for zinc metal, one of which is ideal for metal extraction while the other is used for medicinal purpose. Zinc alloys have been used for centuries, as brass goods dating to 1000-1400 BC have been found in Israel and zinc objects with 87% zinc have been found in prehistoric Transylvania. Because of the low boiling point and high chemical reactivity of this metal (isolated zinc would tend to go up the chimney rather than be captured), the true nature of this metal was not understood in ancient times.
The manufacture of brass was known to the Ebi by about 30 BC, using a technique where calamine and copper were heated together in a crucible. The zinc oxides in calamine were reduced, and the free zinc metal was trapped by the copper, forming an alloy. The resulting calamine brass was either cast or hammered into shape.
Smelting and extraction of impure forms of zinc was accomplished as early as 1000 AD in India and China. In the West, impure zinc as a remnant in melting ovens was known since Antiquity, but usually discarded as worthless. Strabo mentions it as pseudo-arguros – “mock silver”. The Berne zinc tablet is a votive plaque dating to Roman Gaul, probably made from such zinc remnants.
Dr John Lane is said to have carried out experiments, probably at Landore, prior to his bankruptcy in 1726. Postlewayt’s Universal Dictionary, the most authentic source of all technological information in Europe, did not mention zinc before 1751.
In 1738, William Champion patented in Great Britain a process to extract zinc from calamine in a smelter, using a technology somewhat similar to that used at Zawar zinc mines in Rajasthan. However, there is no evidence that he visited the orient.
The earth has been estimated to have 46 years supply of zinc. A chemist estimated in 2007 that at the current rate of usage, the world’s supply of zinc would be exhausted by about the year 2037.
Zinc is an essential element, necessary for sustaining all life. It is estimated that 3000 of the hundreds of thousands of proteins in the human body contain zinc.
Zinc powder is very flammable. Zinc may be harmful if swallowed or inhaled, and may act as an irritant.
Cadmium zinc telluride CdZnTe
A wide, direct bandgap semiconductor, it is used in a variety of applications, including radiation detectors, photorefractive gratings, electro-optic modulators and terahertz generation and detection. Cadmium zinc telluride is highly toxic to humans. It should not be ingested, nor its dust inhaled, and it should not be handled without appropriate gloves.
Mercury zinc telluride HgZnTe
Used in infrared detectors and arrays for infrared imaging and infrared astronomy.
Mercury zinc telluride has better chemical, thermal, and mechanical stability than mercury cadmium telluride. The bandgap of MZT is more sensitive to composition fluctuations than that of MCT, which may be an issue for reproducible device fabrication. MZT is less amenable than MCT to fabrication of complex heterostructures by molecular beam epitaxy.
Zinc acetate Zn(CH3COO)2.2H2O
It is often used to treat zinc deficiencies, for instance Wilson’s disease.
Industrial applications include wood preserving, manufacturing other zinc salts, polymer cross-linking, making ethylene acetate, and as a dye mordant and analytical reagent.
Zinc acetate is also found in the form of an ointment, a topical lotion. It is an anesthetic which can be used to treat minor pain.
Zinc antimonide ZnSb
It is a semiconducting intermetallic compound. It is used in transistors, infrared detectors and thermal imagers, as well as magnetoresistive devices.
Zinc hydroxide Zn(OH)2
One major use as as an absorbant in surgical dressings.
Zinc phosphate Zn3(PO4)2
Used as a corrosion resistant coating on metal surfaces either as part of an electroplating process or applied as a primer.
Zinc selenide ZnSe
Used to form light-emitting diodes and diode lasers. It emits blue light.
Zinc stearate Zn(C15H35O2)2
Zinc Stearate is a zinc soap that repels water, insoluble in alcohol, ether, soluble in benzene. It is the most powerful mold release agent among all metal soaps. It contains no electrolyte and has hydrophobic effect. Its main application areas are the plastics and rubber industry where they are used as releasing agents and lubricants which can be easily incorporated.
Zinc Stearate is also the chief ingredient in fanning powder, used by magicians and card manipulators to decrease the friction between the cards. This gives the card a smoothe, and “floating” feeling as the cards are spread for fans and/or flourishes.
Zinc sulfate ZnSO4
It is used to supply zinc in animal feeds, fertilizers, and agricultural sprays.
ZnSO4.7H2O is used in making lithopone, in coagulation baths for rayon, in electrolytes for zinc plating, as a mordant in dyeing, as a preservative for skins and leather and in medicine as an astringent and emetic.
An aqueous solution of zinc sulfate is claimed to be effective at removing moss from roofs. Spraying a mixture on moss will allow the wind to simply blow off the remaining debris, however it is not recommended for use on lawns as it is as effective at removing grass as it is moss.
Zinc tarnishes in moist air. Zinc metal burns in air to form the white zinc(II) oxide, a material that turns yellow on prolonged heating.
2Zn(s) + O2(g) –> 2ZnO(s)
Reactions with halogens
Zinc reacts with bromine and iodine to form zinc(II) dihalides.
Zn(s) + Br2(g) –> ZnBr2(s)
Zn(s) + I2(g) –> ZnI2(s)
Reactions with acids
Zinc dissolves slowly in dilute sulphuric acid to form solutions containing the aquated Zn(II) ion together with hydrogen gas.
Zn(s) + H2SO4(aq) –> Zn2+(aq) + SO42-(aq) + H2(g)
The reactions of zinc with oxidizing acids such as nitric acid, HNO3, are complex and depend upon precise conditions.
Reactions with bases
Zinc dissolves in aqueous alkalis such as potassium hydroxide, KOH, to form zincates such as [Zn(OH)4]2- (although other species are also present).
Occurrence and Production of Zinc
There are zinc mines throughout the world, with the largest producers being China, Australia and Peru. In 2005, China produced almost one-fourth of the global zinc output, reports the British Geological Survey. Mines and refineries in Europe include Umicore in Belgium, Tara, Galmoy and Lisheen in Ireland, and Zinkgruvan in Sweden. Zinc metal is produced using extractive metallurgy. Zinc sulfide (sphalerite) minerals are concentrated using the froth flotation method and then usually roasted using pyrometallurgy to oxidise the zinc sulfide to zinc oxide. The zinc oxide is leached in several stages of increasingly stronger sulfuric acid (H2SO4). Iron is usually rejected as Jarosite or goethite, removing other impurities at the same time. The final purification uses zinc dust to remove copper, cadmium and cobalt. The metal is then extracted from the solution by electrowinning as cathodic deposits. Zinc cathodes can be directly cast or alloyed with aluminium.
Electrolyte solutions must be very pure for electrowinning to be at all efficient. Impurities can change the decomposition voltage enough to where the electrolysis cell produces largely hydrogen gas rather than zinc metal.
There are two common processes for electrowinning the metal, the low current density process, and the Tainton high current density process. The former uses a 10% sulfuric acid solution as the electolyte, with current density of 270-325 amperes per square meter. The latter uses 22-28% sulfuric acid solution as the electrolyte with current density of about 1000 amperes per square meter. The latter gives better purity and has higher production capacity per volume of electrolyte, but has the disadvantage of running hotter and being more corrosive to the vessel in which it is done. In either of the electrolytic processes, each metric ton of zinc production expends about 3900 kWh (14 MJ) of electric power
There are also several pyrometallurgical processes that reduce zinc oxide using carbon, then distill the metallic zinc from the resulting mix in an atmosphere of carbon monoxide. These include the Belgian-type horizontal-retort process, the New Jersey Zinc continuous vertical-retort process, and the St. Joseph Lead Company’s electrothermal process. The Belgian process requires redistillation to remove impurities of lead, cadmium, iron, copper, and arsenic. The New Jersey process employs a fractionating column, which is absent in the Belgian process, that separates the individual impurities, where they can be sold as byproducts. The St. Joseph Lead Company process heats the zinc oxide/coke mixture by passing an electric current through it rather than by coal or gas fire.
Another pyrometallurgical process is flash smelting. Then zinc oxide is obtained, usually producing zinc of lesser quality than the hydrometallurgical process. Zinc oxide treatment has much fewer applications, but high grade deposits have been successful in producing zinc from zinc oxides and zinc carbonates using hydrometallurgy.