World Mineral Production - NERC Open Research Archive - Natural ...

LEAD
Characteristics
Lead is a dense (11.34 g/cm 3 ), bluish-white metal with little
mechanical strength and virtually no elasticity. It is extremely
soft and highly malleable, with a low melting point (327.4ºC).
When freshly cut the surface has a metallic lustre, but this
quickly tarnishes to dull grey when exposed to air due to
oxidation. It has poor electrical conductivity compared to other
metals. Lead is a potent neurotoxin that accumulates in soft
tissues and bone over time, and this has lead to increasing
restriction in its usage in recent years.
Lead is rarely found as native (free) metal, but is usually
extracted from sulphide ores in which the most common lead
mineral is galena (lead sulphide; PbS). It is usually found in
association with other sulphide minerals also used as ores,
most frequently those of zinc and copper, but also precious
metals. Silver commonly occurs in galena both in solid
solution and as a sulphide phase. Galena is the chief source of
commercial silver output. Other economic lead ore minerals
include cerussite (lead carbonate; PbCO3) and anglesite (lead
sulphate; PbSO 4), commonly found as weathering products
overlying sulphide ore bodies. In terms of mine output lead is
almost always a co-product with other base metals
Lead is obtained from galena by a process called smelting.
This involves roasting the ore to remove the sulphur and to
obtain lead oxide, which is then reacted with coke in a furnace.
The resulting lead bullion contains many impurities such as
silver and gold (hence the name bullion) as well as antimony,
arsenic, copper, tin and zinc. These impurities are then
removed by various refining steps to obtain pure lead (Lead
Development Association International, 2008).
World reserves of lead are 79 million tonnes (Mt), of which
Australia holds 24 Mt, China 11 Mt and USA 7.7 Mt.
Uses
Current global use of lead (Ellis, 2007):
• lead-acid batteries 77%
• pigments 8%
• rolled extrusions 6%
• alloys (including casting) 3%
• shot/ammunition 2%
• cable sheathing 1%
• miscellaneous 3%
The most important use of lead is in lead-acid batteries which
provide ancillary electrical power (chiefly for starting) in
virtually all road vehicles and also in electrically-driven
vehicles. They also provide emergency power in the event of
power failure. Lead’s softness and low melting point make
lead very easy to work hence it has a long history of
exploitation. Its high resistance to corrosion makes it ideal for
weather-proofing buildings and for equipment used in the
manufacture of acids. Lead's high density means that it
absorbs radiation and noise. It is thus used as radiation
shielding in medical applications and the nuclear industry, and
in sound-proofing. Lead chromate (yellow) and lead
molybdate (red/orange) are used as colouring pigments for
ceramic glazes, plastics and to a lesser extent under current
legislation, paints e.g. in road paint. Lead oxide (PbO) in glass
reduces the transmission of radiation, and glasses for VDU
equipment may contain up to 28 per cent PbO (Lead
Development Association International, 2008). Other minor
uses include weights and molten lead is used as a coolant in
fast reactors.
Owing to its toxicity, lead use has become more strictly
regulated and restricted over the last 30 years. Initially, the
change was due to the requirement of US lead consumers to
comply with environmental regulations which significantly
reduced or eliminated the use of lead in non-battery products,
including as a petrol additive, in paints, solders, and water
systems. Lead use is being further curtailed by the European
Union’s RoHS Directive which came into force on 1 July
2006. Lead may still be found in harmful quantities in
stoneware, vinyl (such as that used for tubing and the
insulation of electrical cords), and in brass manufactured in
China. Throughout 2006–2007, many children's toys made in
China were recalled due to lead in paint used to colour the
product; e.g. the toy firm Mattel recalled 55 000 Chinese-made
toys in the US after lead contamination fears (BBC News, 25
October 2007).
World production in 2006
Worldwide production of refined lead was eight million tonnes
in 2006; a 19 per cent increase over 2005 production. Production
increased steadily during the period 2002 to 2006, with
an overall increase of 16 per cent, although levelling out in
2005. China is the top-producing country with 2.7 million
tonnes in 2006. This represents a 14 per cent increase on 2005
and a 106 per cent increase since 2002. The USA was the
second largest producer with 1.3 million tonnes and Germany,
third, with production of 0.3 million tonnes.
The reliance on reliance scrap metal recycling is increasing,
and in 2006 about 50 per cent of refined lead was produced
this way. In the ‘western’ world today more lead is produced
by recycling than by mining (Lead Development Association
International, 2008). Primary (mined) lead production is
dominated by China, Australia and the USA, which together
account for more than half of the total.
Prices
Lead prices started to increase in 2006 after a period of
relative price stability at around US$500 per tonne through the
1990s up until 2003. Prices had doubled by mid-2006 before
the rate of increase began to escalate more dramatically. In
2007 the London Metal Exchange (LME) official price for
lead set record highs, reaching an all-time high of US$3980
per tonne on 15 October as a result of concerns about tight
supplies and expectation of continuing growth in demand. At
the beginning of October, LME stocks stood at just 22 000
tonnes sufficient for less than one day’s global consumption,
and the squeeze on supplies available for immediate delivery
showed no signs of easing (Ellis, 2007).
Prices rose dramatically in response to the suspension of
production at Toronto-based Ivernia Inc.’s Magellan Mine in
Western Australia in March 2007 (Ellis, 2007). This mine
remains the world’s only pure primary lead mine. Output was
suspended after contamination at the Port of Esperance, where
Magellan routes all its exports, when thousands of seabirds
died from lead poisoning. The company was officially blamed
for the contamination in September 2007 (Parliament of
Western Australia, 2007).
Supplies to the world market were further disrupted by an
explosion at Doe Run Resources Corporation’s Herculaneum
smelter in Missouri, USA, which was reported to have halved
production (Mining Journal, 20 July 2007).
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