C6.1 (3) - extractions Flashcards
c6.1.6 - extracting metals c6.1.7 - extracting iron c6.1.8 - extracting aluminium c6.1.9 - biological metal extraction
define an ore
a mineral or rock that contains a high enough amount of a metal/metal compound so that the value of the metal is more than the cost of extracting it
what is the ore to extract copper?
malechite
what is the ore to extract iron?
haematite
what is the ore to extract aluminum?
bauxite
describe the 3 main stages to extract a metal from an ore
1) ore is mined
2) ore is processed
(metal compound removed from rock)
3) metal is extracted from metal compound
what is the mneunomic to remember the metal reactivity series?
(and what does each stand for - in terms of elements)
pink - potassium smiling - sodium cats - calcium meow - magnesium at - aluminium cute - carbon (NOT METAL) zebras - zinc in - iron the - tin long - lead hot - hydrogen (NOT METAL, USED FOR REFERENCE) curly - copper swirly - silver grass - gold privately - platinium
why is carbon used to extract metals instead of electrolysis?
as electrolysis is expensive
- so instead, carbon is used to reduce the wanted metal from its oxide
all metals can be extracted from their compounds using …… but is expensive
electrolysis
why can copper be extracted using carbon, but not sodium?
as copper is less reactive than carbon
- wheras sodium is too reactive to be extracted by reduction
describe the 2 main steps of how copper is extracted from copper sulfide
(and the word and symbol equation for each one)
1) copper sulfide (II) is heated in air
(to get it into metal oxide form for carbon to reduce later)
copper (II) sulfide + oxygen -> copper (II) oxide + sulfur dioxide
2CuS(s) + 3O (g) -> 2CuO(s) + 2SO (g)
2 2
2) copper oxide is heated with carbon
copper (II) oxide + carbon -> copper + carbon dioxide
2CuO(s) + C(s) -> 2Cu(s) + CO (g)
2
explain how the extraction of copper sulfide is a redox reaction
- and what is the reducing agent
- copper(II) oxide loses oxygen and is reduced
- carbon gains oxygen and is oxidised
- carbon is the reducing agent (reduced copper oxide to copper)
what form of carbon is used when extracting copper from copper sulfide?
charcoal
what is the machinery used to extract iron from its ore called?
a blast furnace
what are the raw materials used to extract iron?
and what is each one’s function
- iron ore (haematite - contains iron needed for extraction)
- coke (reduces iron(III) oxide to iron)
- limestone (purifies iron)
describe the three steps in which iron is extracted
- and the symbol equation for each one
1) coke burns in hot air, making carbon dioxide
C(s) + O (g) -> CO (g)
2 2
2) more coke reduces carbon dioxide to carbon monoxide
C(s) + CO (g) -> 2CO(g)
2
3) carbon monoxide reduces iron(III) oxide to iron
3CO (g) + Fe O -> 3CO (g) + 2Fe (l)
2 2 3 2
what is the main reducing agent in the blast furnace for extracting iron from iron(III) oxide?
(and why can it do so)
carbon monoxide
- it is more reactive than iron
in what state does iron leave the blast furnace?
molten state (temperatures are very high, 1500C)
how is extracted iron purified?
- using limestone
1) calcium carbonate decomposes to calcium oxide and carbon dioxide
2) calcium oxide reacts with silica from impurities from extracted iron
how does purified iron leave the blast furnace?
- as molten calcium silicate/slag floats on the molten iron (as it is less dense)
- iron leaves from bottom tube in liquid state
- slag leaves from tube on top of it
what does impure iron contain?
sandy impurities
why is the reaction between calcium oxide and silica a neutralization reaction?
as calcium oxide is slightly alkalinic
and silica is slightly acidic
how does a blast furnace work?
- hot air forced in at the bottom of furnace = high temperature
- raw materials added to top of blast furnace (iron ore oxide, coke, limestone)
- they react together at a high temperature
what is coke?
- a compound made of mostly carbon
- formed by heating coal in the absence of air
why is electrolysis used to extract some metals from their ores?
(and give an example)
if they are more reactive than carbon
ie. aluminum
why is aluminium oxide dissolved in molten cryolite?
- as electrolysis only works if the compound is in solution or molten (so ions can move)
- melting point of aluminium oxide is very high
- and aluminum oxide does not dissolve in water
- cryolite lowers melting point of aluminium oxide from 2000C to 950C
what is the structure which allows aluminium to be extracted from aluminium oxide? (the structure=container where extraction occurs)
(and what is it made of)
(4)
huge electrolysis cell
- carbon anodes
- carbon lining of cell (cathode)
- insulation on outside of cell
- small hole at bottom of cell for purified molten aluminium to flow through
what is produced at the cathode and anode during electrolysis/extraction of aluminium?
(is it oxidation/reduction)
cathode (-) = aluminium ions are reduced (gain electrons)
anode (+) = oxygen ions are oxidised (lose electrons)
2 reasons why extraction of aluminium is expensive
- requires electricity (for electrolysis)
- carbon anodes constantly need replacing as oxygen reacts with carbon to produce carbon dioxide
how is aluminium oxide seperated?
- as in molten state, Al3+ ions and O2- ions are free to move around
- so aluminium is reduced by the carbon lining of cell and becomes molten aluminium
- as it is more dense than the aluminium oxide cryolite solution, it sinks
- and leaves the cell through the tapping hole (molten)
- oxygen ions are oxidised by the suspended carbon anodes
- and later react with the carbon and produce carbon dioxide
environmental downside of extracting aluminium?
released carbon dioxide which is a greenhouse gas
write the half equations that happen at each electrode when aluminium oxide is extracted
cathode:
Al3+ + 3e- -> Al
anode:
2O2- -> O + 4e-
2
what material lines the cathode and anode in the extraction of aluminium?
graphite
name 2 examples of alternative biological methods of metal extraction (and describe each one briefly)
bioleaching
- when bacteria breaks down low grade ores to metal compounds
- and produce leachate solutions with dissolved metal compounds
- this process occurs naturally, but bacteria speed up this reaction
phytoextraction
- when plants absorb metal compounds from low-grade soil
- trapped within leaves/stem
- then burned to extract metlas
how are the metals in bioleaching extracted?
Bioleaching is a technique that makes use of bacteria to extract metals from metal ores
Some strains of bacteria are capable of breaking down ores to form acidic solutions containing metals ions such as copper(II)
The solution is called a leachate which contains significant quantities of metal ions
The ions can then be reduced to the solid metal form and extracted by displacement reactions or electrolysis
This method is often used to extract metals from sulfides e.g. CuS or Fe2S
Although bioleaching does not require high temperatures, it does produce toxic substances which need to be treated so they don’t contaminate the environment
Bioleaching is not only used for the primary extraction of metals, but it is also used in mining waste clean up operations
why do bacteria cause the process of bioleaching to occur?
- similar to how we get energy from respiration
- bacteria get energy from breaking bonds
positives of bioleaching?
- energy efficient (compared to electrolysis)
- cheaper than traditional mining and processing
- no toxic greenhouse gases released
negatives of bioleaching?
- very slow
- toxic substances usually produced (must take care )
what allows metals to be extracted through phytoextraction?
- plant is burned
- ash contains a high concentration of metals
- which are extracted
what does a complexing agent do?
allows plants to absorb ions more easily (during phytoextraction)
positives of phytoextraction? (3-4:
- cheaper than mining or processing
- less energy needed
- close to carbon neutral (carbon dioxide released when burning is absorbed when growing)
- allows a high concentration of metals to be extracted from low grade ores
negatives of phytoextraction? (2-3)
- very slow
- (only certain plants absorb certain metal compound)
- may take many years of replanting and harvesting before plants start taking up the metal compounds
what is good about phytoextraction and bioleaching?
both can extract metals from low-grade ores (which would have been unviable)
- and some ores are becoming scarce
which substance do you use to absorb all water? (compound)
- anhydrous calcium chloride
