Chemistry Assessment Task 2 - Metals
Chemistry Assessment Task 2
Syllabus reference 8.3.5: The relative abundance and case of extraction of metals
influences their value and breadth of use in the community
a. Define the term mineral and ore with reference to economic and noneconomic deposits of natural resources
Mineral – compound occurring naturally, containing commercial metal of
value. Generally found within economic deposits of resources – that is, mineral
has an economic value.
Ore – contains minerals.
Economic deposit – contains ore with a high percentage of the required
mineral, which can be easily extracted.
Non-economic deposits of natural resources do not contain minerals which are
economically viable to extract and produce.
b. Describe the relationship between the commercial prices of common
metals, their actual abundances and relative cost of production
A high cost of production and low abundance of a metal will result in an
increase in the commercial price.
Two main factors affect price: abundance and cost of production.
Abundance:
Abundance – amount of metal that exists in nature.
Economic efficiency – generally ores mined are those which contain high
amounts of the commercial metal, which means that less abundant metals are
generally less mined, and therefore are not as common on the market place,
meaning that the supply for that metal is low, hence increasing its price.
Cost of production:
Factors – reactivity, location, size of ore body, extraction, and production.
Reactivity – less active metals (eg. Gold) are more likely to be found in
their elementary form which requires minimal extraction and production.
Location:
The more remote the mine, the more expensive it will be to
transport products to a refining plant.
High cost of transporting the final product to the consumer,
especially products which are transported to foreign markets.
Size of ore body – a small ore body is less economically efficient,
compared with a larger ore body.
Extraction:
Extraction techniques requiring large amounts of energy are
more expensive than those requiring less energy.
Extraction techniques requiring large numbers of staff are
more expensive than those requiring smaller number of staff or
a larger amount of computerised tasks.
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Production – complex refining techniques requiring multiple steps, large
amounts of energy or manpower, are expensive which effects the overall cost
of production.
Example – Aluminium & Gold:
Metal
Aluminium (Al)
Gold (Au)
Commercial Price
(AUD/tonne)
2040
26 474 850
Cost of production
(AUD/tonne)
1632
9 700 350
From the table above, it is clear that the commercial price of gold is far greater than
the commercial price of aluminium. Aluminium is far more abundant than gold and is
therefore more widely available, hence decreasing the commercial price. In addition
to this, the cost of production of gold is almost 6000 times greater than that of
aluminium, which can be attributed to factors such as location and the extraction
process. As such, the commercial price for gold is far greater than that of aluminium.
c. Explain why ores are non-renewable resources.
Non-renewable resource – a finite resource: one which cannot be replaced
once it is used.
Ores formed by geological processes (eg. Crystallisation of molten rock).
There is no way to replicate these processes i.e., no further ores can be
produced.
Not seen as issue in same context as oil or petrol, but is still an issue as one
day the earth will have mined all ores in the long-term future.
In the future it will be less economically viable to mine ores, as society will be
forced to mine ores which contain increasingly smaller percentages of minerals.
d. Describe the separation processes, chemical reactions and energy
considerations involved in the extraction of copper from one of its ores.
Extraction of copper from chalcopyrite (CuFe2) occurs using processes such
as: mining & crushing, froth flotation, roasting & smelting and electrolytic
refining.
Mining & Crushing:
Copper ore contains approximately 0.5% copper and 99.5% unwanted rock.
To help separate the mineral copper from the gangue, the ore is crushed and
ground to form ball mills (0.3mm particle size).
Froth Flotation:
Milled ore is mixed with collectors – water, detergent and oils.
Copper adheres to bubbles.
Bubbles rise to surface and are removed.
Ore contains approximately 30% copper after this process.
Gangue removed from bottom of tank and transported for further processing.
Roasting & Smelting:
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Concentrated, dry, mineral is combined with coal, lime and sand.
Sulfides and oxides of copper and iron form, by roasting the mixture in an
oxidising atmosphere at 1000ºC.
Combustion of coal releases heat, the sand and lime act as a fluxing agent,
which removes the impurities of the iron eg. Iron(II) silicate.
Formed (copper matte)– mixture of copper(I)oxide and copper(I) sulphide
(containing approximately 50 – 70% copper).
Copper matte mixed with additional sand and smelted again to produce molten
copper metal (98% pure).
Air blown through molten copper at 1400ºC, converting sulfides to sulphur
dioxide.
Electrolytic Refining:
Copper from smelter moulded into anodes and a pure copper sheet forms the
cathode, in an electrolytic cell. (Refer to figure 1)
Oxidation occurs at the anode and reduction occurs at the cathode, forming a
pure layer of copper at the cathode. That is, copper transfers from the impure
anode and forms pure copper at the cathode.
A sludge is formed containing valuable metals (eg gold and silver) which are
less active than copper.
Impurities are left behind in solution (eg iron) which are more active than
copper.
Chemical Reactions:
Roasting:
2Cu2S(l) + 302 (g) → 2Cu2O(l) + 2SO2 (g)
Smelting:
2Cu2O(l) + Cu2S(l) → 6Cu(l) + SO2 (g)
Slag Formation:
CaO(s) + SiO2 (s) → CaSiO3 (l)
FeO(s) + CaSiO3 (l) → FeSiO3 (l) + CaO(s)
Anode:
Cu(s) → Cu2+(aq) + 2eCathode:
Cu2+(aq) + 2e- → Cu(s)
Energy Considerations:
Electrolytic Refining – requires large amounts of energy and therefore factors
must be considered. For example, placing the refinery in a location where cheap
electricity is available.
Coal – significant amounts of coal are used in the smelting stage of the
process, and the cost of acquiring, storing and transporting coal must be
considered throughout the process.
Total amount of energy required and associated costs are factored into the
commercial price of copper.
Eg. To produce 1t of copper (from an ore body) requires 10^5MJ – two to
three times less than that of Aluminium.
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Figure 1 – Wheel used to cast the anodes
e. Recount the steps taken to recycle aluminium.
Points to consider re: Al Recycling:
Most common metal recycled – in Australia >60% aluminium products are
recycled.
High cost of production results in need for recycling.
Energy required to recycle aluminium is 5% of that needed to extract bauxite.
Collection:
Aluminium products, such as drinks cans and car parts, are collected through
council initiatives, as well as individuals and organizations.
Sorting and Separation:
Aluminium does not contain magnetic properties, however steel does - steel is
removed from the products using a magnetic separation technique.
To ensure that alloy s of aluminium remain constant, used aluminium cans are
separated from other aluminium products.
Preparation:
Aluminium cans and all other aluminium products are compressed to form
bales (a separate bale is used for aluminium cans) and are then transported to
plants for further processing. (Refer to figure 2)
Remelting & Refining:
Baled aluminium is fed separately into a rotary finance, which reaches
temperatures of 780ºC, melting the aluminium. (Refer to figure 3)
Molten aluminium is then cast into ingots, which are then sent to create new
drink cans, kitchenware and other aluminium products.
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Figure 2 – Bale of aluminium cans
Figure 3 – Rotary Furnace
f. Discuss the importance of predicting yield in the identification, mining
and extraction of commercial ore deposits.
Overview of Yield:
Yield (chemical/reaction yield) – during chemical experiment, the amount of
product obtained.
Formula: actual yield / theoretical yield X 100 = Yield Percentage
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Actual yield – in either grams or moles (molar yield)
“The theoretical yield value always relates to one of the reactants. This is
usually the limiting one, taking into account the molar relation of the reactants and
the stoichiometry of the reaction”
(http://en.wikipedia.org/wiki/Yield_%28chemistry%29)
Identification:
Determining economic viability of the deposit:
Amount of mineral to be obtained per reaction
Calculate expected returns
Cost per unit of ore
Mining:
Type of mining used, eg. A higher yield means that the mining process is able
to be less precise and more efficient, as a larger percentage of minerals can be lost
in this process, when compared with an ore containing a smaller yield.
Extraction:
Location – a commercial ore deposit with a high yield, means that large
amounts of mineral will be produced, and as such it is more economically viable
to have the extraction facility close to consumers or the refinery, in order to save
transport costs. This is not as great an issue for deposits with a lower yield, as
transportation costs will already be relatively low.
Type of extraction – predicting the yield for different extraction methods and
selecting one, which creates the most product for the cheapest price.
g. Justify the increased recycling of metals in our society and across the
world.
In recent years there has been a trend for an increase in recycling, mainly due
to an increase in public awareness of the benefits (‘current argument’) of
recycling, outlined below.
This increased awareness has arisen as a result of organisations such as Planet
Ark and media involvement such as Channel Ten’s provision of prime time to
community and environmental messages.
Australia currently recycles 2 billion aluminium cans a year (63% of total).
Worldwide recycling occurs, eg, USA recycled 62.6 billion aluminium cans in
2004.
Current Argument:
Recycling is a cleaner and financially superior method of obtaining aluminium
as it:
Saves energy and resources
Embodies financial benefits – world wide
Embodies environmental effects – world wide
Energy & Resources:
Recycling consumes less water than the extraction of aluminium:
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This energy is produced by non-renewable resources such as coal,
and therefore is a non-sustainable method, which in turn impacts upon
the environment.
Extraction of aluminium produces greenhouse gases (through the
burning of fossil fuels for energy) and as such, recycling eliminates the
emission of such gases and hence combats global warming.
Decreases the use of valuable resources such as coal and natural
gas.
Recycling consumes less water than the extraction of aluminium:
Copious amounts of water are consumed in the extraction of
aluminium through froth flotation.
This is particularly important in Australia as it is currently
experiencing a drought, and as such water is a valuable resource, not to
be misused.
Recycling one aluminium can saves enough energy to operate a television for
three hours.
Financial Benefits:
Currently, bauxite deposits that are being mined are those with large
percentages of aluminium in them. As these deposits are mined, in the future,
less economic deposits, that is, those with a lower percentage of aluminium
will have to be mined. As such aluminium will become less abundant, hence
more valuable and therefore more expensive to the consumer.
Each year, Australia recycles 2 billion aluminium cans with a total value in
excess of AU$33million.
Other countries are also economically benefiting, with the USA recycling a
massive 62.6 billion aluminium cans in 2004, worth over one billion dollars.
In Australia, recycled aluminium is exported and through this means, is
generating large amounts of money and positively impacted upon the
Australian economy, with benefits flowing into society.
Recycling plants produce jobs, which is positive for both society and the
economy.
Environmental Benefit:
Recycling produces no waste, whereas extraction produces tailings and
other waste, which must be stored in landfills.
Population trends indicate that the world has a growing population, and as
the population exponentially increases, land will become a viable asset. As
such it is important to reduce landfill sites which are avoidable.
For example, bauxite is generally mined using an opencast system (refer to
figure 4), which disrupts the ecological processes of the land and causes
habitat destruction. This method had a detrimental impact upon the
environment.
For every 1tonne of aluminium, which is recycled, 5 tonnes of bauxite is
preserved. Therefore, the amount of bauxite mines required is dramatically
reduced, leading to a decrease in the number of mines and hence negative
ecological impacts.
Recycling produces approximately 5% of the CO2 that is produced by raw
extraction methods.
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A majority of the benefits outlined, effect nations worldwide (with all benefits
effecting Australia) and hence recycling is something which should occur and be
promoted in all countries across the globe. This will ensure environmental
sustainability, in regard to the world’s resources, including aluminium.
Figure 4 – Opencast mine – note the extensive invasion of the land.
Figure 5 – Recycling of selected materials: 1984 – 2003 (UK) – The graph depicts how the United
Kingdom has increased its recycling of aluminium in recent years, along with other products such as
paper and cardboard, whilst some products, such as lead and ferrous, decreased.
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h. Analyse information to compare the cost and energy expenditure involved
in the extraction of aluminium from its ore and the recycling of
aluminium.
Method of acquisition
(Aluminium)
Energy (MJ) required
per tonne
Extraction
65 000
Recycling
800
Figure 5 – Table outlining energy required to obtain aluminium through different methods.
Compared with the extraction of aluminium from ores such as bauxite,
recycling is a superior method as it is more cost effective and energy
efficient.
Extraction:
Cost:
Process – opencast mining, which involves the removal of all topsoil and
vegetation and soil beneath. This is an expensive method, as it requires
expensive machinery and large numbers of man-hours. Eg. In Australia
16 000 people are employed in bauxite mines.
Land must be purchased, which can cost millions of dollars.
Transportation – it is expensive for ores to be transported from the mine to
the refinery.
Exports – large costs involved in freighting minerals (eg. Specialised
equipment required) to foreign countries, such as the USA.
Environmental costs: large cost to the environment, mainly in the form of
land degradation.
Bayer Process – used to convert bauxite into alumina (Al2O3) requires large
amounts of chemicals such as sodium hydroxide, which must be
purchased and hence is an additional cost to extraction.
Waste – expensive to dispose of. For example, Fe2O3 is formed during the
refining process, and must be transported and pumped into disposal
ponds.
10 tonnes of bauxite are required to produce 1 tonne of aluminium, using
this process.
Total cost – AU$1 632 per tonne.
Energy:
Bayer Process – (refining of bauxite to produce alumina) requires 15 000 MJ of
energy per tonne.
Electrolytic reduction – (refining of alumina to produce aluminium) requires
100 000 amps per tonne.
Refineries and smelting factories often require their own power plant, due to
the large amounts of energy that they require.
Total energy – 65 000 MJ per tonne.
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Recycling:
Cost:
Minimal transportation costs, compared with the extraction method.
Less machinery required.
In puts (used cans and other aluminium products) are free, whereas the
extraction method requires land to be purchased.
As 95% of aluminium cans and scrap metal is recycled, recycling is decreasing
the impact on the environment, as these products do not need to be placed in
landfills.
Recycling centres can be established in any location, thus reducing the impact
on the environment.
No chemicals are required to be purchased.
Energy:
Requires 5% of energy used for extraction – approximately 19 times less
energy used.
Only energy required is used to heat and melt the aluminium, which in
comparison to the large amounts of energy used in the many processes involved
with the extraction method, is a minimal amount.
Total energy – 800 MJ
Overview:
Recycling aluminium is a superior alternative to raw extraction, as a means of
producing aluminium for use in society. This is attributable to the lower costs and
energy required to recycle aluminium, hence ensuring its sustainability and
limiting its impact upon the environment.
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Bibliography
"Copper(II) Carbonate." Wikipedia. 23 July 2006
<http://en.wikipedia.org/wiki/Copper_carbonate>.
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ml>.
"Gold Price Australia." Gold Price. 23 July 2006 <http://goldprice.org/gold-priceaustralia.html>.
Jayaweera, Keshani. Metals. 2005. 23 July 2006
<http://boredofstudies.org/download.php?id=4567>.
Planet Ark. 25 July 2006 <http://www.planetark.org/>.
Tregarthen, Linden. Preliminary Chemistry. 1st ed. Sydney: Macmillan, 2003.
"Visy Recycling: Aluminium and Steel." Visy. 25 July 2006
<http://www.visy.com.au/divisions/category_page.aspx?did=1&sid=3&cid=8
9&scid=93>.
Why Recycle?" Aluminium Can Group. 30 July 2006 <http://www.aluminiumcans.com.au/RecycleCentre.html>.
"Yield (Chemistry)." Wikipedia. 30 July 2006
<http://en.wikipedia.org/wiki/Yield_%28chemistry%29>.
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