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 55% zinc.

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 levels.

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 by-product.

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)
-construction material
-brass
-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 deficiencies.