Tungsten - Mining Journal

DEPOSITS
All tungsten deposits are of magmatic
or hydrothermal origin. Although
more than 30 tungsten-bearing
minerals are known, only two of
them are important for extraction:
wolframite (Fe, MnWO4) and
scheelite (CaWO4). The concentration
of these minerals in workable
ores is usually 0.3-1% WO3.
Wolframite is a general term
for iron and manganese tungstates
where the iron/manganese ratio can
vary. A mineral with more than 80%
FeWO4 is called Ferberite and a
mineral with more than 80% MnWO MnWO4
is called Hübnerite.
During cooling of the magma,
differential crystallisation occurs, and
scheelite and wolframite are often
found in veins where the magma
has penetrated cracks in the earth’s
crust. Most of the tungsten deposits
are in younger mountain belts, for
example the Alps, Himalayas and the
Pacifi c rim.
World tungsten resources have been estimated at
7Mt W, including deposits that have so far not been
proven to be economically workable. It is suggested
that 30% of the resources are wolframite and 70%
are scheelite ores. The former mineral contains
76.5% WO3, while the latter contains 80.5% WO3.
There are major deposits of these minerals in China
(with about 57% of the world total), Russia, Austria
and Portugal.
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OVERVIEW
WANTED
Tungsten was an important metal
during the Second World War
(as a raw material for the
weaponry industry) and, as the
main European source of the
element, Portugal was put under
political pressure from both sides.
PRODUCTION
China is today by far the largest supplier of primary
tungsten. The other principal producing countries are
Austria, Bolivia, Canada, Portugal and Thailand. Mines
have closed in recent decades in Australia, Brazil,
France, Japan, South Korea, Sweden and the US.
The extraction of tungsten has several stages,
the ore being converted to tungsten oxide (WO2),
which is heated with hydrogen or carbon, producing
powdered tungsten. It can be used in that state or
converted into solid bars.
Ammonium Paratungstate (APT) is usually
calcined to yellow (WO3) or blue oxide (WO3-X, a
slightly substoichimetric trioxide with varying oxygen
content). The yellow or blue oxide can be reduced to
APT
Ammonium Paratungstate is the main intermediate
product and the main tungsten raw material traded
in the market. (NH4)10(H2W12O42).4H2O
June 2008 Mining Journal special publication Tungsten
The Tungsten Tree, published in 1944 by Wah Chang
Steel branch
Carbide branch
tungsten-metal powder
in either ‘pusher’
Tungsten ore
furnaces (in which the
powder passes through
the furnace in boats) or
in ‘rotary’ furnaces, at
700-1,000°C.
Most of the tungsten-metal
powder is
converted to tungsten
carbide (WC) by reaction
with pure carbon
powder (eg carbon black) at 900-2,200°C in pusher
or batch furnaces, a process called carburisation.
Tungsten carbide is, quantitatively, the most important
tungsten compound. Because of its hardness, it is
the main constituent in cemented carbide.
Scrap recycling is an important factor in the world’s
Estimated world tungsten
reserves 7Mt (W content)
South
America
Other
Canada
4%
12%
17%
US
4%
CIS
6%
China
57%
Compounds
Non-ferrous alloys
tungsten supply. It is estimated that some 30% is
recycled, and the tungsten-processing industry is able
to treat almost every kind of tungsten-containing
scrap and waste to recover tungsten.
Sources: North American Tungsten Corp, ITIA
Supply in 2004: 56,700t
(W content)
11%
Other
CIS
6%
83%
China