Mineral resources

Which 5 metals are extracted most from the lithosphere

Iron (1700m/t), aluminium (53m/t), copper (19m/t), zinc (14m/t) and lead (9m/t)

3 uses of iron

• steel reinforced concrete in buildings

• manufacture of ships in transport

• appliance cases for cookers

2 uses of aluminium

• packaging foil

• vehicle window frames

2 uses of copper

• electric cables

• water pipes

2 uses of zinc

• steel protection: galvanising batteries

• alloys e.g. brass

3 uses of lead

• lead-acid batteries

• radiation shielding

• roof/window flashing in construction

6 construction materials most often extracted from the lithosphere

aggregates (40b/t), limestone (600m/t), salt (290m/t), gypsum (180m/t), sulphur (75m/t) and kaolin (26m/t)

3 aggregates (sand and gravel) uses

• concrete

• building mortar

• glass

3 limestone uses

• cement

• crushed for road surfacing

• building bricks

3 salt uses

• source of chlorine for water sterilisation

• de-icing roads

• food additive

2 gypsum uses

• building plaster

• food additive

2 sulphur uses

• sulphuric acid manufacture to make phosphate fertilisers

• pest control

3 kaolin uses

• filler and coating for paper

• ceramics e.g. porcelain

• filler in cosmetics

Mineral ore

a rock or sediment that contains one or more valuable minerals concentrated above background levels

Lasky’s principle

in general, as the purity of a mineral decreases, the amount of mineral present increases exponentially

Cut off ore grade

the amount of ore needed in a deposit for it to be mined economically

Reserve

the amount of the resource that can be exploited now, economically, using existing technology

Inferred reserve

the presence of the mineral can be predicted from knowledge of the geological structures present but not enough is known to estimate the amount that can be economically extracted

Probable reserve

sufficient information about the deposit is known, so the amount of mineral that can be economically extracted can be estimated with sufficient accuracy that further exploration is justified

Proven reserve

sufficient exploration has been carried out, including trial drilling, to accurately estimate the amount of mineral that can be economically extracted

3 factors that limit the viability of exploitation

• absence of technology required to exploit the deposits

• financial cost of exploitation too great

• environmental impact of exploitation unacceptable

Resource

all the material that is theoretically available for exploitation that cannot yet be exploited but likely can be in the future

Stock

all the material that exists in the lithosphere

Deep mining

mining under special conditions

Open-cast mining

a method of extracting minerals from a pit dug into the ground

Dredging

removing sediments and debris from the bottom of water bodies

Hydrothermal deposition (igneous)

the process by which rocks and minerals are created by the cooling and hardening of magma or molten lava e.g. basalt, diorite, granite

Hydrothermal processes (metamorphic)

pre-existing rocks are altered by processes within the Earth such as tectonic movements of crustal plates e.g. quartzite, soapstone, marble

Proterozoic marine sediments (sedimentary)

dissolved iron compounds become oxidised by the oxygen released by photosynthesis, producing insoluble iron deposits e.g. hematite, magnetite

Alluvial deposits (sedimentary)

materials that were carried and separated by flowing water e.g. gold, diamonds

Evaporites (sedimentary)

if a bay of an ancient sea became isolated, then the water may have evaporated, leaving crystallised minerals. Evaporites also form in inland seas in desert areas as the water from inflowing rivers evaporates e.g. halite, calcite, gypsum

Secondary enrichment (sedimentary)

economically important metals can form minerals that are soluble or insoluble, depending upon the conditions. They may be transported in solution, by moving water, and then deposited as their oxidation state changes e.g. oxides, sulphates, carbonates

Biological sediments (sedimentary)

living organisms form mineral deposits. These processes often concentrate minerals that can be deposited in sedimentary rocks e.g. chalk, coal, crude oil

IR spectroscopy 

different minerals emit infrared radiation at different wavelengths, and these can be used to identify them

Gravimetry 

using a GRACE satellite, gravimeters detect variations in gravity caused by variations in density and mass. Igneous rocks are usually more dense than sedimentary deposits

Magnetometry 

a survey that measures the Earth’s magnetic field and looks for variations caused by magnetic ore bodies

Seismic surveys 

involve sound waves produced by controlled explosions, or a seismic vibr4tor on the surface. The echoes can give info about the depth, density and shape of rock strata

Resistivity 

the measurement of the difficulty with which electricity passes through a material. In general, sedimentary rocks have lower resistivities than igneous rocks because they have higher water contents

Trial drilling

once another method has been used to locate a potential site for mineral extraction, trial drilling is used to determine the depth, purity and chemical form of the deposits by drilling multiple bore holes in the area. Most expensive technique

Chemical analysis

laboratory tests confirm the chemical composition and purity of the minerals in the rock samples 

How does ore purity affect mine viability

the purity of the ore affects the financial costs of exploitation and the environmental impacts of mining

Effects of a low ore grade deposit

• more rock will have to be mined

• more spoil produced

• more energy needed for mining and processing

• more pollution generated

How does chemical form affect mine viability

affects the ease of chemical extraction of the metal. E.g. aluminium can be extracted from bauxite (aluminium oxide) but not from clay (alumino-silicates), which is more abundant

How does overburden and hydrology affect mine viability

overburden is the rock that lies above a mineral deposit. Hard overburden may require blasting which increases costs. Loose overburden may increase the risk of landslides, so the sides of the mine void may be landscaped at a gentler gradient. This may increase the overall area of the mine. Higher precipitation or impermeable rocks below may increase drainage costs

How does depth affect mine viability

costs rise rapidly as depth increases. Doubled depth = cost much more than doubles. Sides of the mine can’t be vertical due to the risk of collapse. Amount of rock that must be removed to reach the mineral rises rapidly as depth increases. As depth increases, amount of water that flows into the mine from surface runoff/ groundwater also rises, increasing pumping costs significantly

How does the cut-off ore grade affect mine viability

mining must be an economically profitable activity, so there must be a balance between production costs and income. The lowest ore purity that can be mined economically, using existing technology, is called the cut-off ore grade (COOG). The COOG changes as technology improves and market prices fluctuate

How do transport costs affect mine viability

transport costs are affected by the distance to market, the ease of bulk transport, the presence of a suitable existing transport infrastructure and whether the bulk of the mineral has been reduced by processing

How do market economics affect mine viability

Market demand + sale value of minerals control the economic viability of exploiting a specific mineral deposit. The market price is controlled by the demand for the mineral, how much is produced + the costs of extraction/ processing. The amount that can be supplied increases relatively slowly as mines are developed but demand can rise and fall quickly. When demand and supply don't match, prices can fluctuate widely

Environmental impacts of mining (13)

land take, habitat loss, GGs, habitat fragmentation, loss of amenity, dust pollution, noise pollution, turbid drainage water, spoil disposal aesthetic, spoil disposal stability, spoil disposal leachate, mine site restoration

How can the impact caused by land take be reduced

 Respecting land deeds and planning around communities

How can the impact caused by habitat loss be reduced

Considering nearby wildlife and their environment. Habitat restoration when mining has ended

How can the impact caused by greenhouse gases be reduced

Operational efficiency (less unsuccessful mining), electrification and using more renewable energy resources

How can the impact caused by habitat fragmentation be reduced

Avoid mining in the middle of a habitat, create biological corridors, restore the habitat after mining

How can the impact caused by loss of amenity be reduced

Landscaping or tree planting. Turning the old mine into a community resource. E.g. the Eden Project

How can the impact caused by dust pollution be reduced

Water sprays can be used to limit the dust by making dust particles heavier, so they settle and clump together

How can the impact caused by noise pollution be reduced

Embankments or “baffle mounds” help to absorb and deflect noise. Blasting at set times of day so it is predictable.

How can the impact caused by turbid drainage water be reduced

Use sedimentation lagoons where the water stands still long enough for the solids to sink, this decreases the turbidity of the water.  

How can the impact caused by spoil disposal aesthetic be reduced

Landscaping can make the spoil heap look more natural and blend in with the surrounding area

How can the impact caused by spoil disposal stability be reduced

landscaping to reduce gradients and by adding soil so trees and vegetation can grow

How can the impact caused by spoil disposal leachate be reduced

Mine drainage water can be passed through a filter bed of crushed limestone to immobilise the metal and prevent it being carried into rivers

How can mine site restoration decrease the impacts of mineral extraction

• many sand, gravel and clay pits have been flooded and developed as wetland wildlife reserves

• urban development on mine sites may be possible if the ground is stable

• agricultural use may be possible if: landscape isn’t too steep/uneven, no toxic materials present, soil sufficiently fertile

2 improvements in exploratory techniques

better remote sensing image resolution and portable field equipment

2 improvements in mechanisation

using machines in deep mining and using machines in open cast mining

5 methods of exploiting low-grade deposits

bioleaching, phyto mining, electrolysis, leachate collection, polymer absorption

Bioleaching

The use of living organisms to extract metals from their ores. Examples: acidophilic bacteria and aspergillus fungi. Sulphuric acid dissolves metals in the ore. The metals in the leachate produced by bioleaching can be separated by electrolysis or by using carbon filters. Bioleaching doesn’t require high temps

Phyto mining

some plants absorb metal ions from soil/water/spoil heaps and concentrate them in their structure. Can be used as a method of decontaminating polluted sites and as a method of commercial extraction of metals. Once the plants have absorbed the metals, the vegetation is harvested and incinerated. The concentrated metals in the ash can be dissolved using acids to produce leachate which is then separated using electrolysis

Iron displacement

iron is a more reactive metal than copper and will displace copper ions from solution. The solid iron goes into solution as the copper ions are deposited as solid copper metal which can be collected

Leachate collection

Rainwater percolating through spoil heaps dissolves soluble metal ions. The draining leachate can be recirculated through the spoil heaps to increase the concentration of metal ions in the solution. When the concentration is high enough, the metals can be extracted from the solution by electrolysis

Polymer adsorption

metal ions dissolved in seawater will adsorb onto the surface of some polymers and can be collected later. Synthetic polymers can be used, as can natural polymers such as lignin from wood and chitin from discarded shrimp shells. This method is being used to extract uranium and may provide a low-energy method of producing fuel for the nuclear power industry

Polymetallic nodules

metal-rich nodules found on the ocean seabed. Usually small and very deep. Recovering nodules disturbs the seabed. Large scale exploitation is expensive and requires international agreement on ownership of seabed + its resources

2 environmental impacts of extracting polymetallic nodules

• recovering nodules disturbs seabed and kills benthic organisms that live there

• separating nodules from seabed sediments increases water turbidity. Re-deposition of sediments may kill filter feeders

Pre-consumer recycling wastes

materials that have not been used yet

post-consumer recycling wastes

discarded consumer products

Advantages of recycling metals

• recycled materials are lighter to transport

• labour costs are lower

• energy is saved

Disadvantages of recycling metals

• bulk transport is not possible during collection

• more energy used on transport

• alloys of mixed metals aren’t easily separated

• post-consumer recycling schemes require cooperation from the public

• not all used materials can be recycled as some are lost

Cradle to Cradle design

products are designed so the materials can be reused at the end of their useful lives, includes easy separation of components and identification of materials