is a light, grey metal, which is relatively easy to extract. The
density of zinc is 4,7 g/cm3. Zinc is naturally present in the environment
and is the 24th most abundant element in the earth’s crust.
The average concentration of zinc is calculated to be 70 mg/kg.
At the mine, zinc is found in form of zinc blende (a sulphide of
zinc is exposed to moist air, a thin film of hydroxide and carbonate
is formed on the surface. The film has a low solubility in water
and protects the zinc from further corrosion. If high amounts of
sulphur dioxide are present in the atmosphere, zinc sulphates form
on the surface. Zinc sulphate has higher solubility in water and
is more easily washed away, so a fresh zinc surface is exposed to
corrosion. However, the level of atmospheric sulphur dioxide has
decreased considerably in both Europe and the Nordic countries during
the last 20 years and today very low concentrations are measured.
Zinc in organisms
participates in numerous vital reactions, such as phosphorus metabolism,
nucleic acid metabolism, protein and DNA synthesis, detoxification
reactions etc. In higher animals and humans, zinc is important for
vital brain functions, the immune system and reproduction. In presence
of organic substances, zinc ions create complexes together with,
for example, amino acids and proteins. This affinity to bio molecules
is the reason for the important role zinc plays as an essential
micronutrient for all types of organisms. There are 300 different
enzymes, in which zinc is known to play a catalytic, structural
or controlling role.
need 12-15 mg zinc per day to maintain necessary biological functions
and to avoid zinc deficiency. This means that, for example in Sweden,
the inhabitants consume about 50 tonnes of zinc during a year. Unfortunately
a lot of people in the world suffer from zinc deficiency, which
for children leads to diarrhoea, stunted growth and other problems.
Zinc is also used in wound creams, body lotions, baby powder, medicine,
sun oils and so on.
1. Humans need 12-15 mg zinc per day to maintain necessary biological
functions and to avoid infections.
plants, zinc deficiency leads to significantly decreased growth.
To counteract this, thousands of tonnes of zinc are added to fields
in fertilizers. In animal breeding, for example, sucking-pigs get
zinc in their food to boost immune defence, growth and skin condition.
For this purpose alone, about 70 tonnes of zinc are consumed in
Sweden each year.
systems for assessment of the environmental hazard of chemical substances
include as a central criterion the bioaccumulation potential of
the substance. This is normally expressed as the substance’s
bio concentration factor (BCF) and is determined experimentally
by exposing aquatic organisms to an aqueous solution of the
substance in question. If the BCF value > 100 the substance is
considered as having such a high bioaccumulation potential and it
can be regarded as environmentally hazardous, according, for example,
to the EU directives (26).
substances, such as essential metals, whose uptake and accumulation
in living organisms is controlled by sophisticated regulation systems,
the use of the BCF is of very limited relevance for assessment of
environmental hazard. This becomes evident when it is observed that
the experimentally-determined BCF value for an essential metal
such as zinc shows a very great variation, depending on how the
bioaccumulation experiment is carried out. A test organism that
is exposed to a low zinc concentration in water absorbs and accumulates
more zinc to satisfy its zinc need, resulting in a higher BCF value
• Series of experiments with molluscs showed that the BCFs
for zinc varied between 600 and 55,000 in the common sea mussel
and between 1,100 and 9,000 in a gastropod species after 8
days of exposure to zinc, despite the fact that the zinc content
in the body tissue only varied by a factor of 2.
For a type of shell, the BCFs for zinc varied between 1100 and 9000
after 8 days of exposure to zinc, despite the fact that the zinc
content in the shell only varied by a factor of 2.
is therefore important to take account of zinc’s role as an
essential element when applying regulatory criteria.
Fields of application
major application of zinc is for corrosion protection of steel in
the form of a coating or as metallic powder in paint, in brass or
in other zinc alloys. Zinc chemicals are used in a lot of different
areas such as medicines, creams, wood protection chemicals, catalysts,
food nutrients for humans and animals, rubber additives etc. Zinc
oxide is the most common additive in rubber production, skin protection
and wound creams.
Sweden, 70 % of zinc is used for corrosion protection. A major part
of that volume is used for galvanizing of steel sheets and in construction.
The annual consumption of zinc in Sweden is 35 000 tonnes and
most of this is imported from Norway or Finland.
Production and energy consumption
is mainly produced from the ore sphalerite, which after crushing,
concentration and roasting is dissolved in an electrolytic solution.
Recycled zinc from, for example, steel-making dust and other raw
materials are dissolved directly into the electrolyte. The zinc
is separated from the solution using an electric current. Metallic
zinc is precipitated onto aluminium cathode plates. The cathodes
are then removed from the solution and replaced with new cathodes.
The zinc is stripped from the aluminium plates, smelted and cast
into ingots. After all the stages in this process are complete,
the zinc is a finished and saleable product. The zinc used for hot-dip
galvanizing has a purity of 99.995 % of zinc. The remaining 0.005
% consists mainly of iron.
Swedish Environmental Protection Agency has made a calculation of
the relative energy need during primary production of zinc and concluded
that its energy consumption is the lowest for all base metals, except
iron, calculated both on weight and volume percent. According to
one zinc-producing company, the energy consumption is 12-13 GJ per
tonne of zinc. Recycling of zinc from galvanized steel sheet only
consumes 5 % of the energy given above. Because of that, zinc is
very advantageous compared to other base metals, regarding conservation
of environmental resources.
hot dip galvanizing some process waste, or rather secondary raw
materials, are generated, from which all the zinc can be recycled.
a total world annual zinc demand, about 35 % is met by recycled
zinc. Zinc’s cycle life is on average 30 to 40 years - which
means that almost 80 % of available zinc is recycled. Zinc in used
chemicals and the small quantities of zinc which slowly weathers
from coated steel is not recycled. This is the same for zinc pigments
lost through degradation of paints.
can be recycled infinitely without deterioration in quality. This
means that zinc fits well into a sustainable society. By protecting
steel from corrosion for many decades, iron, energy, transport and
emissions of mainly carbon dioxide, are reduced.
2. Almost 80 % of all available zinc is recycled.
Emissions of zinc
emissions are principally of two different kinds – emissions
to air and emissions to water. In Sweden, zinc emissions to water
are largely from point sources, in particular from the waste and
forestry industry. The main part of zinc emissions to air are created
by waste-fed steel processes working without filters, and from fire
wood and peat. The surface treatment industry has very effective
cleaning equipment and the yearly emission of zinc (2002) in Sweden
is only two tonnes. A large hot dip galvanizing plant in Sweden
today has an annual emission of zinc of about 20-25 kg, which is
four times lower than the limit set by the Swedish Environmental
3 and 4 shows how the emissions to air and water have changed during
the period between 1977 and 2000. To air, the decrease is a factor
of 12 and to water a factor 4.5. The lower decrease in emissions
to water is because the Falu Mine still has a release of zinc to
the environment, even though zinc has never been produced there.
emissions of zinc are mainly from corrosion, traffic wear (tyres,
asphalt, brake lining) and household drainage. A large part also
comes from atmospheric deposition, caused by emissions in other
countries. The trend is decreasing and the diffuse emissions have
been lowered by 40 % during the last 10 years.