to the extraction of metals
methods can use in extracting metals from mineral ores?
The Earth's crust contains many different
Rocks are a mixture of minerals and from some we
can make useful
A mineral can be a solid metallic
or non–metallic element or a compound found naturally in the
Mineral ores are naturally occurring rocks
that provide an economic starting
point for the extraction and manufacture of metals for a huge variety of
purposes ie a metal ore is rock containing sufficient metal to be worth
extracting the metal from it.
The simplest definition of an ore is a
mixture of a metal containing mineral and other materials ('minerals')
from the surrounding rocks, which can be described as impurities with
respect to what you want from the ore.
Metal ores are obtained by mining and that
this may involve digging up and processing large amounts of rock.
Most ores are mined have to
be concentrated before the metal is extracted and purified.
results in lots of waste material that must be dealt with from an
environment of view.
social, economic and environmental impacts of
exploiting metal ores are discussed on a separate page.
The rock must contain enough
of the metal compound, hence enough of the metal, to be worth exploiting
the ore reserve and extract the metal by physical and chemical
The metal ore, a mineral or mixture of
minerals from which economically viable amounts of metal can be extracted, i.e. its got to have enough of the metal, or one of its
compounds, in it to be worth digging out!
Ores are often oxides, carbonates or sulphides.
These ores are all
finite resources so we should use them wisely!
Any ore must contain
enough of the metal to make it worthwhile to mine and then extract the
High grade ores will
therefore be the most economical to exploit BUT over time the better
quality–richer sources will decrease, especially with the power of the
global economy and powerful and growing economies of Brazil, China,
India and other Asian economies.
The economics of metal
extraction are not only dependent on the quality of the ore and the
cost of extraction (ie richer ores lead to cheaper production), but also
depend on the market price and demand. If demand is high the metal price
rises and may off–set the price of mining lower grade ores, but if
demand is low, the metal price falls and inefficient mines and smelters
will go out of business ie its not worth extracting the metal. Of course
it is possible to improve the technology of metal extraction and enable
companies to produce more metal from the ore than was previously
possible and even utilise low grade ores previously discarded and not
considered worthwhile mining.
Since the majority of
metals are found combined with non–metals like oxygen (oxide ion) or
sulfur (sulfide ion) or the carbonate ion, chemical reactions are needed
to free the metal from its mineral source.
In order to extract a
metal, the ore or compound of the metal must undergo a process
called REDUCTION to free the metal i.e.
The oxide/sulfide loses oxygen/sulfur, to form the free
metallic atoms, or
the positive metal ion gains
negative electrons to form the neutral metal atom.
that removes the oxygen from an oxide is called the reducing
agent i.e. carbon, carbon monoxide or sometimes
REDOX notes at the end of
the metal reactivity series page, and on this page
technology and science have developed the methods of extraction
have improved to the point were all metals can be produced. The
reactivity is a measure of the ease of compound formation and
stability (i.e. the more reactive the metal, the more readily the
metal forms a stable compound eg with oxygen or sulfur, and
therefore this greater compound stability, the more
difficult it is to reduce to the compound to the metal).
reactive metals such as gold, silver and copper have been used for
the past 10000 years because the pure metal was found
Conversely, the more
reactive a metal, the stronger it bonds to other elements like
oxygen and sulfur, therefore it is far less likely such a metal is
found as the uncombined element AND the more reactive a metal the
more difficult it is and more costly to extract it.
Moderately reactive metals like copper, iron, lead, tin
have been extracted using carbon based smelting for the past 2000–3000
BUT it is only in the last 200 years that very reactive metals
like sodium or aluminium have been extracted by electrolysis.
In other words, our
exploitation of metal mineral resources as developed and
expanded as the technology of metal extraction has also
developed and improved.
Therefore the economics
of extraction may change over time with eg reduced costs by
technological advances or increased by depletion of high grade ore
The depletion of high
grade ore reserves has resulted in technology research increasingly looking at ways of
extracting metals from low grade ores which were previously
uneconomic to use.
The crucial point is that
generally speaking, the
method of extraction depends on the metals position in the reactivity
The reactivity series of
metals can be presented to include two non–metals, carbon and
hydrogen, to help
predict which method could be used to extract the metal.
most metals occur as compounds, some metals are so
unreactive that they do not readily combine with oxygen in the air
or any other element
present in the Earth's crust, and so can be found as the metal
itself (sometimes referred to as 'native' metal).
For example, a metal, most frequently found as the
is gold (and sometimes copper and silver)
and no chemical separation is needed.
In fact all the
metals below hydrogen can be found as the 'free' or 'native' element,
though they occur mainly as compounds combined with non–metals like
oxygen (oxide ion) or sulfur (sulfide ion) or the carbonate ion in
this point we need to say more about oxidation and reduction and redox
One definition of
oxidation is oxygen gain.
Somewhere in the past
aluminium combined with oxygen to form aluminium oxide, the main
compound in bauxite ore from which aluminium is extracted.
aluminium + oxygen ==>
We would therefore say the
aluminium was oxidised by oxygen gain.
Therefore to extract
aluminium we must reduce it and remove the oxygen.
One definition of
reduction is oxygen loss.
Copper ores are processed to
give copper oxide from which copper may be obtained by a reduction
process to remove the oxygen (reduction). This can be done by heating
copper oxide + carbon ==>
copper + carbon dioxide.
Here the copper oxide is
reduced by oxygen loss, and the carbon is the 'oxygen remover' and
is referred to as the reducing agent.
Similarly in a blast
furnace, the iron oxide is reduced with carbon to free the iron from
The method employed to
extract a metal by a reduction process largely depends on its reactivity
See a separate page for a detailed
discussion of oxidation, reduction and REDOX reactions
Metals below carbon
in the reactivity series (see table on right) can be extracted by heating the oxide with carbon or carbon monoxide. The non–metallic elements
carbon will displace
the metals less reactive than carbon in a smelter or blast furnace
iron or zinc and metals lower in the series.
like iron, copper, tin, lead, zinc can readily be extracted by
reaction–reduction of their e.g. oxides using cheap carbon (i.e.
coke made from coal).
Iron ore is
used to make iron and steel and iron is produced in a blast
furnace by reducing iron oxides with carbon and it is the carbon
that removes the oxygen from the iron oxides – the carbon is
known as the reducing agent.
The metal copper can be easily extracted
copper–rich ores are becoming scarce so new methods of extracting copper are
being developed to exploit low grade ores.
hydrogen will not displace hydrogen from acids. Their oxides
are easily reduced to the metal by heating in a stream of
hydrogen, though this is an extraction method rarely used in
In fact most metal oxides below carbon can be reduced
when heated in hydrogen, even if the metal reacts with acid.
carbon in the reactivity series
cannot usually be extracted
with carbon or carbon monoxide.
So, metals more reactive
than carbon are usually extracted by electrolysis
of the purified molten ore or other suitable compound.
Electrolysis is the
process of breaking down a compound using electrical energy and is
needed to extract the most reactive metals.
The process of
electrolysis uses of large amounts of energy in the extraction
of these reactive metals and makes them expensive to produce.
The metal ions in the
ore compound are forced by electrical energy into accepting
electrons and producing free metal atoms.
Aluminium is a very useful metal but expensive to produce.
from molten aluminium oxide or sodium from molten sodium chloride.
The ore or
compound must be molten or dissolved in a solution in an
electrolysis cell to allow
free movement of ions (electrical current). The conducting melt
or solution is called the electrolyte. Theory given in the
Because these reactive
metals cannot be obtained by relatively cheap carbon reduction
methods, their extraction tends to be more costly due to more
specialised stages in the extraction process, more energy is
needed (maybe costly electricity) and more costly specialist
chemicals like a more reactive metal or chlorine (remember
carbon–coke is relatively cheap e.g. as used in the blast
furnace extraction of iron).
Other methods are used in
special cases using the displacement rule.
A more reactive
metal can be used to displace and extract a less reactive metal but these are
costly processes since the more reactive metal also has to be produced
in the first place!
Titanium is another very useful metal but expensive to produce.
is used to purify less reactive metals which have previously been
extracted using carbon or hydrogen (e.g. copper and
Electrolysis is also used to plate one metal with another.
The demand for raw
materials does have social, economic and environmental implications
conservation of mineral resources by recycling metals, minimising
Metals can be mixed together
to make alloys to improve the metal's properties
to better suit a particular
WHERE NEXT? Other
associated KS4 Science GCSE/IGCSE chemistry web pages on this site
Notes information to help revise KS4 Science
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360 Science/IGCSE Chemistry & OCR 21st Century Science, OCR Gateway Science WJEC/CBAC
GCSE science–chemistry CCEA/CEA GCSE science–chemistry
(and courses equal to US grades 8, 9, 10) also useful revising and introduction to
metal extraction for A level AS/A2/IB chemistry students
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Introduction to how metals are obtained
from the ore, the method e.g. carbon reduction or electrolysis,
depends on the chemical reactivity of the metal
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