Mining and Sustainable Development II - DTIE

Mining
Table 1
World production of selected mineral commodities in 1998 and 1999
Mineral 1998 1999 (estimates)
Metals
Chromite* 12,700 thousand tonnes 12,800 thousand tonnes
Cobalt* 26,300 tonnes 28,300 tonnes
Copper 12,200 thousand tonnes 12,600 thousand tonnes
Gold 2,460 tonnes 2,330 tonnes
Indium 230 tonnes 240 tonnes
Iron ore 1,020 million tonnes 992 million tonnes
Lead 3,100 thousand tonnes 3,040 thousand tonnes
Manganese 3,090 thousand tonnes 2,910 thousand tonnes
Mercury* 2,320 tonnes 2,300 tonnes
Molybdenum 135,000 tonnes 129,000 tonnes
Nickel 1,140,000 tonnes 1,140,000 tonnes
Platinum group metals (PGM) 269.000 tonnes 275,000 tonnes
Rare Earths (REO content) 76,600 tonnes 76,500 tonnes
Silver* 16,400 tonnes 15,900 tonnes
Tin 206,000 tonnes 210,000 tonnes
Tungsten 32,200 tonnes 31,300 tonnes
Vanadium 41,800 tonnes 40,000 tonnes
Zinc 7,550 thousand tonnes 7,640 thousand tonnes
Industrial Minerals
Asbestos 1,840 thousand tonnes 1,790 thousand tonnes
Cement 1,520,000 thousand tonnes 1,560,000 thousand tonnes
Fluorspar 4,4670 thousand tonnes 4,220 thousand tonnes
Gypsum 107,000 thousand tonnes 108,000 thousand tonnes
Potash (K2O equivalent) 25,100 thousand tonnes 25,200 thousand tonnes
Salt 186,000 thousand tonnes 200,000 thousand tonnes
Sulphur (all forms) 57,800 thousand tonnes 55,900 thousand tonnes
Energy Minerals
Coal (all types) 4,655,234 thousand tonnes data not available
* World total does not include estimates from output from China
Tonnes = metric tonnes
PGM includes platinum and palladium only
Principal source: United States Geological Survey
prevented if there is an appropriate management
system; others, such as habitat destruction at the
mine site, can generally be dealt with after closure
through site rehabilitation.
Air pollution
The main air quality issue is the dust produced by
the working of open pits and by crushing and
grinding operations. Dust can also be given off by
tailings dams. Workers and nearby communities
can be affected by dust in the atmosphere. In addition,
particle fall-out around mine sites can contaminate
soils and water and damage vegetation.
Mines are also sources of greenhouse gas emissions.
CO 2 is produced by energy use and methane
is sometimes released from underground operations,
especially in coal mines. In the past, some
deep mines used ozone-depleting CFCs in refrigeration
systems. This practice has now largely ceased.
Smelting (the process in which ore is heated for
the purpose of separating it from the gangue) produces
very large amounts of air pollutants. Worldwide,
the smelting of copper and other non-ferrous
metals releases an estimated 6 million tonnes of
sulphur dioxide (SO 2 ) into the atmosphere each
year – 8 per cent of total worldwide emissions.
Non-ferrous smelters also emit large quantities of
arsenic, lead, cadmium and other heavy metals
except where highly efficient pollution control
equipment is used. Smelters may also be regional
pollution “hot spots”, whose emissions cause severe
local environmental damage as well as contributing
to more distant or global phenomena such as
acid rain and climate change.
Water pollution
Potential sources of water pollution from mining
include drainage from surface and underground
mines, wastewater from beneficiation, and surface
run-off. A particular problem is acid mine
drainage. Many mining operations, especially
those extracting ores that contain sulphides, such
as nickel, copper, iron, zinc, cadmium, lead and
coal (if pyrites are present), may produce acidic
and metal-bearing solutions resulting from the
natural oxidation of the sulphides through exposure
to air and water. The combination of acids
and metals can have severe effects on the ecology
of local watercourses, and the metals can enter and
bioaccumulate 1 up the food chain. Acid mine
water can be a problem for drainage from both
underground and surface workings, as well as
drainage from waste rock stock piles and concentrator
tailings deposits. It can occur while the
mine is operating and even long after its closure,
unless specific measures are taken.
Mineral separation processes that make use of
dangerous and toxic chemicals such as sulphuric
acid or cyanide (e.g. leaching) or organic reagents
(e.g. flotation) can be serious sources of contamination
if appropriate control systems are not in
place. Furthermore, much mine wastewater contains
large amounts of suspended solids (ranging
from colloidal to settleable materials) originating
from the ore itself, from waste material, or from
surface installations. These solids can affect aquatic
flora and fauna and physically choke local
waterways and lakes.
In addition to causing water pollution, excavations
can also influence the hydrology around the
excavated area. Excavations may lead to more
rapid seepage into the groundwater, causing nearby
streams or wells to become dry. Underground
works may cut across aquifers and bring otherwise
separate bodies of water into communication.
Solid waste
Open pit operations produce far more waste per
tonne of ore than underground operations, where
there is no overburden and where some of the
removed material can be used to backfill excavations
as work progresses. Heaps of mine waste
occupy large amounts of land and disfigure the
landscape. They are also a source of dust and water
pollution. Inert material carried away in run-off
water can clog rivers and streams. If the wastes
contain sulphides, acid drainage can occur –
sometimes for many years – due to reaction with
rainwater,.
Tailings
The tailings that remain after extraction and processing
are mostly muds and slurries containing a
very high proportion of extremely finely ground
material. Due to their vast quantities, liquid
nature and very high content of fines (finely
crushed coal or ore), their containment and control
are an ongoing management concern at virtually
all mine sites (see related articles in this
publication).
The separation processes used for most metals
do not extract all of the minerals present. Tailings
therefore contain quantities of metals and other
minerals, as well as residues of the chemicals used
to extract them. The finely ground material from
processing makes contaminants formerly bound
up in solid rock (such as arsenic, cadmium, copper,
lead and zinc) accessible to water. Acid
drainage, which exacerbates contamination by
heavy metals, is often a problem when tailings are
exposed to the atmosphere. It arises from the sulphide
minerals that are often associated with the
commonly mined ores of many metals including
copper, gold, lead, nickel and zinc.
Tailings are therefore more usually dumped in
heaps, released into ponds, or retained by tailings
dams. In some cases, submarine disposal or release
6 ◆ UNEP Industry and Environment – Special issue 2000