General Information of Zinc
(from the National Institute of Health, World Health
Organization, and International Zinc Association)
The history of Zinc
Centuries before zinc was discovered in the metallic form, its
ores were used for making brass and zinc compounds were used for healing wounds
and sore eyes. Brass was produced by the Romans in the time of Augustus (20 B.C.
- 14 A.D.). By 1374, zinc was recognized in India as a new metal and at Zawar,
India, both zinc metal and zinc oxide were produced from the 12th to the 16th
century. From India, zinc manufacture moved to China in the 17the century. Zinc
was recognized as a separate metal in Europe in 1546. In 1743, the first
European zinc smelter was established at Bristol in the United Kingdom.
Sources of Zinc
Ores containing zinc are widespread geologically and
geographically and many ore bodies are still awaiting development when
sufficient demand occurs.
The abundance of zinc in the earth's crust is approximately 132ppm with the
major types of zinc ore deposits being:
-Volcanic-hosted massive sulphides
-Sediment-hosted massive sulphides
-Mississippi Valley Type ("MVT") carbonate-hosted deposits
-Intrusion-related zinc ore deposits
-"Broken Hill type" ore deposits.
Usually zinc ores are found in association with those of lead,
copper, gold, silver as well as other metals. Rarely is the ore, as mined, rich
enough to be used directly by smelters; it needs to be concentrated. Typically
zinc ores contain 3% to more than 10% zinc and zinc concentrates will contain
How is Zinc mined?
Zinc ores are being mined in more than 50 countries with
Australia, Canada, China, Peru and the U.S.A. being the leading producers. Owing
to the nature of the ore veins, most zinc mines are underground but some new
mines are of the open pit type. It is estimated that underground mining is
performed in 80% of zinc mines, 8% as open pit, with the remainder being a
combination of underground mining and open pit mining. In terms of production
volume, however, open pit mines account for as much as 15% with underground
mines producing 64%. 21% of mine production comes from the combination of
underground and open pit mining.
How is Zinc produced?
The raw material used for the production of zinc is zinc concentrate, which is
the result of a flotation process after the ore has been mined and milled. The
zinc ore contains 1-15% zinc whereas the concentrate typically contains approx.
55% zinc, 6.5% iron and 32% sulphur together with other elements at much lower
The process begins with the roasting of the concentrate. At a temperature of
around 950°C, oxidisation of the zinc, iron and sulphur occurs. The sulphur is
collected as SO2 and is used to make sulphuric acid (H2SO4) - a commercial
The iron and zinc oxides that, after the roasting process, have been reduced to
powder form, are leached with dilute sulphuric acid. The solution is neutralised
and the precipitates i.e. metallic co-products together with any unwanted
contaminants, are removed by filtration.
The refined solution is then electrolysed in a cell fitted with a lead anode and
an aluminium cathode. The cathode is immersed in the solution for 48 hours
during which time the zinc is deposited on the aluminium cathode from which it
is subsequently stripped.
The final process takes place in the foundry where the zinc takes its final
form, either as a metal with a purity of 99.95% or as an alloy together with
copper, aluminium or magnesium. The zinc is cast into various forms (normally
ingots or plates)with weights from 9 kg to 4 tons.
What are the major uses of Zinc?
The major uses of zinc are:
-anti-corrosion coatings on steel (galvanizing)
-precision components (die casting)
-pharmaceuticals and cosmetics
-micronutrient for humans, animals and plants
What is the importance of Zinc for health?
Zinc is essential for human health. It is vital for many biological functions
such as disease resistance, wound healing, digestion, reproduction, physical
growth, diabetes control, taste and smell. Every cell in the human body requires
zinc to multiply and more than 300 enzymes need zinc for proper functioning.
What are the effects of Zinc Deficiency?
The World Health Organization's "World Health Report 2002" estimated that
one-third (33%) of the world's population is at risk of inadequate zinc intakes.
The effects of zinc deficiency may be severe, ranging from impaired
neuropsychological functions, growth retardation and stunting, impaired
reproduction, immune disorders, dermatitis, impaired wound healing, lethargy,
loss of appetite and loss of hair.
Zinc deficiency in agricultural soils is also a major worldwide problem -
affecting , both crop yield and quality. Severe soil zinc deficiency can cause
complete crop failure whilst losses of up to 30% can occur in yield of cereal
grains in crops such as wheat, rice and maize as a result of even mild