Extraction of metals Flashcards
What 2 states can metals be in?
- combined state
- uncombined state
What metals are in an uncombined state?
unreactive metals:
- gold
- platinum
- silver
What metals are in a combined state?
mineral ores containing:
- metal oxides
- metal sulfides
- metal carbonates
- metal chlorides
Where are most metals found?
- in the ground
What are metals first combined with?
non metals:
- oxygen
- sulfur
- carbon
What are metal + non-metal compounds called?
- ores
What are the 3 main stages involved in obtaining metals from their ores?
- concentrating the metal ore
- extracting crude metal from ore
- refining crude metal
What happens in stage 1 (concentrating the metal ore)?
- earth and rock are removed before the metal is extracted from the ore
- this causes the metal ore to contain little waste materials
What happens in stage 2 (extracting crude metal from the ore)?
- the metal is extracted by reduction with carbon or using electricity
- dependant on the position of the metal on the reactivity series
What happens in stage 3 (refining crude metal)?
- other methods such as electrolysis have to be used to further refine metal to obtain pure metal
- this is due to the metal that is extracted from the ore potentially still containing impurities
What are the 2 methods of extraction for metals in their combined states?
- reduction with carbon
- electrolysis
What is the process of reduction with carbon?
- heating the metal compound with carbon
What is the process of electrolysis?
- using electricity to decompose the molten metal compound
What is the relationship between how easy it is to extract a metal from its ore and the position of the metal on the reactivity series?
- the higher up a metal is on the reactivity series, the more difficult it is to extract from its ore
Why is a metal higher up on the reactivity series more difficult to extract from its ore?
- the stability of an ore of a metal higher up the reactivity series is greater than one lower down
Which redox reaction happens when a metal is extracted from its ore?
- reduction
Why does reduction occur when a metal is extracted from its ore?
- the metal ion (in the ore) has to gain electrons to form a metal atom
what metals require electrolysis to extract the metal from its ore?
- metals high up in the reactivity series
- (K - Al)
What metals can be extracted from its ore using reduction with carbon?
- middle order metals
- (Zn - Pb)
What metals can be extracted from its ore by simply heating it?
- metals at the bottom of the reactivity series
- (Cu-Ag)
What is an ore of iron?
- haematite
Where is iron extracted from its ore?
- in the blast furnace
What are the raw materials present at the top of the blast furnace?
- haematite (Fe2O3)
- coke (C)
- limestone (CaCO3)
What is the blast furnace lined with?
- refractory materials
- e.g. aluminium oxide, magnesium oxide
Why is the blast furnace lined with refractory materials?
- high melting point
- traps heat
What are the reactions that occur in the blast furnace?
- production of carbon dioxide
C(s) + O2(g) —> CO2(g) - production of carbon monoxide
CO2(g) +C(s) —> 2CO(g) - reduction of iron ore
Fe2O3(s) +3CO(g) —> 2Fe(l) + 3O2
how is carbon dioxide produced in the blast furnace?
- coke burns in hot air
- carbon dioxide is produced
What kind of reaction is the production of carbon dioxide (exothermic/endothermic)?
- highly exothermic
- temperature in this part of the furnace rises to 1900 degrees celcius
How is carbon monoxide produced in the blast furnace?
- carbon dioxide reaction with hot coke to produce carbon monoxide
How is an iron ore reduced in the blast furnace?
- carbon monoxide (powerful reducing agent) reduces iron(lll) oxide to molten iron
Where does molten iron go?
- falls to the bottom of the blast furnace
- tapped off
Why is limestone present in the furnace?
- to remove impurities
What is the main impurity in iron?
- sand (silicon dioxide)
what happens to limestone inside the furnace?
- it decomposes to quicklime (calcium oxide) and carbon dioxide
What is slag?
- calcium silicate
How is slag formed?
- calcium oxide reacts with silicon dioxide from sand in iron ore to form calcium silicate (slag)
What is slag used for?
- used in road foundations
Where does slag go in the blast furnace?
- floats on top of molten iron
What is carbon dioxide considered as?
- hot waste gas
Where does carbon dioxide escape from and what else escapes with it
- from the top of the furnace
- together with nitrogen and carbon monoxide
What is the purity state of iron produced in the blast furnace?
- impure
What are the impurities in iron produced in the blast furnace?
- carbon
- other non-metals
What is impure iron produced in the blast furnace called?
- cast iron
- pig iron
What are the characteristics of pig iron/cast iron?
- very brittle
- has limited uses
What happens to pig iron/cast iron?
- converted into steel
What is mild steel?
- low carbon steel
What are the characteristics of mild steel?
- malleable
- easy to shape
What is mild steel used for?
- making car bodies
- machinery
What is the relationship between the amount of carbon added and the strength of the steel?
- the more carbon added, the stronger the steel
Why is steel stronger when more carbon is added?
- carbon impurity strengthens the iron lattice
- makes it difficult for atoms to slide over one another
What are the characteristics of high carbon steel?
- strong but brittle
Why is high carbon steel brittle?
- too much disruption of layers
- when a force is applied, metal fractures
What is high carbon steel used to make?
- cutting and boring tools
- e.g. knives, hammers, chisels etc
What are the properties of stainless steel?
- durable
- resistant to corrosion
What is stainless steel used for?
- cutlery
- surgical instruments
What are the essential conditions for rusting?
- oxygen
- water
what is rust?
- hydrated iron(lll) oxide
What speeds up rusting?
- presence of sodium chloride
- presence of acidic substances
What are the different methods of prevention of rusting?
- placing a barrier around the metal
- sacrificial protection
- using a rust-resistant alloy such as stainless steel
What are some examples of placing a barrier around the metal?
- painting
- greasing
- covering with plastic
- electroplating
How is sacrificial protection done?
- a more reactive metal (like magnesium or zinc) is attached to the iron object
Why does sacrificial protection work?
- more reactive metal corrodes in preference to the iron
How is galvanised steel produced?
- dipping steel into molten zinc
- oxidises more readily than iron
What is sacrificial protection useful for?
- underground steel or iron objects like pipes or storage tanks
Why is sacrificial protection useful in certain cases?
- when objects are difficult to paint or grease
- but easy to attach a piece of magnesium or zinc
Why does sacrificial protection work?
- more reactive metal loses electrons more readily than iron
Why should we recycle metals?
- metal ores are a finite resource
- we should recycle metals whenever possible
- world’s reserves of metals may last longer if we substitute metals with other materials or recycle old metal objects
What are commonly recycled metals?
- aluminium (drink cans)
- iron (scrap metal)
- lead (car batteries)
What are the advantages of recycling metals?
- recycling helps conserve limited metal and fossil fuel resources
- extracting metals uses up fossil fuels for energy production
- recycling helps reduce environmental problems caused by extraction of metals
- smelting ores causes air pollution
- mined land cannot support plant and animal life
- lots of waste material generated from extraction process (90% of extracted metal ore turns out to be waste)
- recycling saves cost of extracting metals
- landfill sites are required for disposal of used metal objects and waste material from metal extraction
What are the economic impacts of recycling metals?
- recycling can be more expensive than extracting metals from their ores
- costs are incurred to collect, sort, separate, clean and transport old metal
What are the social impacts of recycling metals?
- time and effort are needed for communities and businesses to practice recycling as a lifestyle
What are the environmental impacts of recycling metals?
- recycling can cause pollution problems
- e.g. harmful gases for produced when lead from car batteries is recycled
