Resources
and Environment
Three stages in resource
exploitation:
exploration à
extraction à processing
à use
cyclic in the sense that
as resources become used have to look for more. All of these stages except exploration have
considerable impact on the environment. Pollution (or contamination) is one of major
problems. Not a new problem (eg.
mercury in streams of Sierra Nevada in 1849 gold rush). but scale of modern
extraction processing and use of resources brings bigger scale problems.
Extraction methods
–mining and Drilling
Underground vs open
pit and strip-mining
In US 90% of mines are
open pit, rest of word about 50% open pit. Reason is not geological, rather it
is to do with wages and safety regulations. Labor cheaper in LDC's, safety not
always as well regulated
Open Pit methods
Quarry
Overlying rock
–overburden- must be removed to get at the ore. Overburden/ore known as stripping ratio
Earth moving equipment or
blasting used to break overburden/ore, debris trucked away. Pumping of excess water needed in deep
pits
Strip Mining - horizontal beds only, overburden can be replaced which is
environmentally better
Dredging when water
in pit
Hydraulic high pressure
hoses to disaggregate the rock
eg . Bingham Canyon 4km x 1km. stripping ration 3:1 meant moving 400,000 tons per
day./ Total of 6 billionmetric
tons moved.
Underground mines
Shaft, Adit, stope, Decline
Pumping of water
essential in underground mine
Air circulation and
conditioning
Dangers: cave-ins, gas explosions(esp. coal),
fires
Variations: in situ leaching, solution mining
Drilling for
hydrocarbons
Well drilling used for
the extraction of gaseous and liquid resources – principally hydrocarbons
(petroleum and natural gas), but also for water.
Methods – drill
pipe + bit, derricks
Environmental effects
of extraction
Land use:
Open pit mine means
disruption of landscape. May be
disruption of water table and water supplies (need a lot of water to mine)
How big a problem?
US: about 3700km2 occupied by mines - approx 0.26% of land area
compare
with
2500 each for airports and railroads
13,500
for roads
100,000
national parks
385,000
wilderness areas
World between 1976 and
2000 about 37000km2 - about 2% of land surface
Underground mining
Less problematic , but
still create waste heaps of non-economic rock(tailings)
Surface subsidence when
underground mine collapses.
Health concerns: dust (silicosis, anthracosis,
pneumonosis (black lung disease), lung cancer)
In US, Surface mining and
reclamation act of 1977 ensures an env. impact statement is prepared before
mining proceeds, also land has to be restored to original form after mining.
Many
other countries have similar laws.
Reclamation
plan and bond often required
older sites not covered
by this - may be good side; can be used for municipal waste
Toxic wastes
Concern is with toxic materials released during mining
process. Minerals previously at depth are now at surface.
Oxidation
of ores may cause acids to develop.
High
levels of toxic heavy metal compounds - released into environment. Clean up after mining entails
neutralizing these.
Environmental impact
of hydrocarbon drilling
Environmental hazards
much less than for mining – relatively rare but are still some
problems: eg. blowouts,
fires
Many more problems in transportation of hydrocarbons eg. Exxon Valdez 1989
Processing of
resources
As ores occur as oxides,
sulfides etc need processing to form metal
Two step process beneficiation (concentration) of
ore,then smelting
Beneficiation
ore concentrated, gangue
minerals removed
("tailings")
· comminution: crushing and milling
• magnetic
separation,
• density
separation,
• froth
flotation
• leaching
(eg cyanide process with gold)
Smelting
ore to metal
pyrometallurgy heat
+ carbon; produces metal,
slag and waste gases
hydrometallurgy ore
dissolved in acids to make solution, then preciptate
metal on electrodes
Environmental effects
of processing
Beneficiation uses a lot
of water, waste water is often contaminated by toxic heavy metals. Some may also be radioactive with long half lives.
Smelting is very
polluting. - gas dust
In past, SO2 in
particular eg Sudbury
Ontario surrounded by 100km2 of barren land + further 360km2 of stunted
woodland; Ducktown, Tennessee same situation
Acid rain. many lakes in Canada Scandinavia low
Ph(Ph=7 neutral, less is acid, more is alkali) . Modern methods have improved the situation greatly removal
of SO2 has been very successful (response to clean air act)
Leaching have been accidents where cyanide
escaped.
Environmental effects
of Resource use
Fossil fuels (coal and
hydrocarbons)
Smog
Acid rain (SO2
in coal)
?Global warming - possibly related to greenhouse effect
caused by CO2 produced by burning fossil fuels
Nuclear fuels
problem of disposal: eg. Yucca Mountain, Nevada
General solid waste
disposal or recycling
Disposal of ariticles
made from resources a problem – although if recycled waste products can
be seen as a resource
US: 5 billion tons per year – agricultural,
mineral (tailings) also domestic/municipal - latter has potential for recycling
Sanitary landfill no is
main method in industrialized nations:
area method –
modified version of this used in Florida
trench method
ramp method
all have some sort of
lining, and cells
incineration reduces
volume (up to 90%), may generate power. High toxicity of ash (which may escape
into the atmosphere). Heavy metals; PVC makes HCl gas
recycling
on the rise since mid 80’s partly because of rising conciousness,
partly because technology has made it economic (especially if offset by
alternative cost of constructing landfills. However situation still plagued but economic
problems and lack of markets for recycled material
Liquid waste disposal
Exploration
Methods
Geology
Mineral deposits tend to
form in specific geological environments.
Key is to study deposits already discovered, try to understand them;
then apply this to newly discovered prospects
eg. mineral zonation a clue in hydrothermal
deposits
field investigations -
maps etc; geological sections
drill holes (boreholes) -
vertical control
Geochemistry
Especially with
hydrothermal deposits, rocks/soil tainted with elements
Stream surveys
Soil surveys
Pathfinder elements
Geophysics
Gravity
Magnetic
Electrical
Seismic
Deposit
Evaluation
Drilling
Reserve
estimations: volume and grade
Environmental
Impact