Metals and their uses: Extracting metals.
Metals are very useful.
Naturally found rocks which contain enough metal/metal compounds to make extracting it economical are called ores.
Most everyday metals are mixtures called alloys.
Metals and metal compounds (such as gold, iron oxide and aluminium oxide) are found in the crust of the Earth.
Ores are mined.
They may need to be concentrated before the metal is extracted and purified.
The economics of using a particular ore may change as time goes by.
E.g. If a metal becomes rare, an ore may be used when it was considered earlier to be too expensive to mine.
Metals and their uses: Reactivity and Extraction M
Metals = produced when metal oxides are reduced (have their oxygen removed).
The reduction method depends on the reactivity of the metal.
For example, aluminium and other reactive metals are extracted by electrolysis.
Iron and other less reactive metals may be extracted by reaction with carbon/carbon monoxide.
The method of extraction of a metal from its ore depends on the metal's position in the reactivity series.
Gold is found as the native metal (not as a compound) because it is so unreactive.
It does not need to be chemically extracted from its ore, but chemical reactions may be needed to remove other elements that might contaminate the metal.
Metals and their uses: Transition Metals
Located in the centre of the periodic table - between groups 2 and 3.
Most metals are transition metals - e.g. Iron, Titanium and Copper.
They are obviously all metals and are all good conductors of heat and electricity.
They can be hammered or bent into a shape very easily.
Useful as construction metals.
Useful for making objects that heat or electricity have to pass through - wires, radiators etc.
Metals and their uses: Iron.
The process of extracting iron from an iron ore is done in a blast furnace.
Iron ores (such as haematite) contain iron oxide.
The oxygen must be removed from the iron oxide to leave the iron behind. Reactions in which oxygen is removed are called reduction reactions.
Carbon is more reactive than iron, so it can displace the iron from iron oxide. Here are the equations for the reaction:
iron oxide + carbon → iron + carbon dioxide (2Fe2O3 + 3C → 4Fe + 3CO2)
In this reaction, the iron oxide is reduced to iron, and the carbon is oxidised to carbon dioxide.
In the blast furnace, it is so hot that carbon monoxide will also reduce iron oxide:
iron oxide + carbon monoxide → iron + carbon dioxide (Fe2O3 + 3CO → 2Fe + 3CO2)
Metals and their uses: Copper
Copper is useful for wiring because it is soft and can be very easily bent. It's also a good conductor of electricity.
Copper is also useful for plumbing and making pipes and water tanks as it doesn't react with water and is a good conductor of heat.
Some copper ores have a really high concentration of copper. This makes them copper rich.
We extract copper from these ores by a process called smelting - this is done in a furnace.The copper is then purified using a process called electrolysis.
Solutions containing copper compounds (like copper sulphate) have electricity passed through them. During electrolysis, positively charged copper ions move towards the negative electrode and are deposited as copper metal.
There is a low amount of copper-rich ore. We are currently researching to find new ways of extracting the copper from the low-grade ores in an environmentally friendly way. This research is very important, as traditional mining involves huge open-cast mines that produce a lot of waste rock.
Metals and their uses: Phytomining, Bio-Leaching a
Some plants' roots are able to absorb copper compounds. They concentrate these compounds as a result of this.
The plants can be burned to produce an ash that contains the copper compounds. This method of extraction is called phytomining.
Some bacteria can absorb compounds of copper. They then create leachates - solutions containing copper compounds. This method of extraction is called bio-leaching.
Copper can also be extracted from solutions of copper salts using scrap iron. Iron is more reactive than copper, so it can displace copper from copper salts. For example:
iron + copper sulfate → iron sulfate + copper.
Metals and their uses: Aluminium and Titanium.
Aluminium and titanium are two metals with a low density. This means that they are lightweight for their size.
They also have a very thin layer of their oxides on the surface, which stops air and water getting to the metal, so aluminium and titanium resist corrosion.
Aluminium is used for aircraft, trains, overhead power cables, saucepans and cooking foil.
Titanium is used for fighter aircraft, artificial hip joints and pipes in nuclear power stations.
Unlike iron, aluminium and titanium cannot be extracted from their oxides by reduction with carbon. Existing methods are expensive because: the processes have many stages and large amounts of energy are needed.
Aluminium is extensively recycled because less energy is needed to produce recycled aluminium than to extract aluminium from its ore
Recycling preserves limited resources and requires less energy, so it causes less damage to the environment.
Metals and their uses: Alloys
Adding elements to a metal will change the properties of it. If a mixture contains two or more elements - and one of them is a metal - then it is called an alloy. The sizes of the atoms in an alloy vary, which distorts the regular arrangements of atoms. This makes it more difficult for the layers to slide over each other, so alloys are harder and stronger than the pure metal.
Pure copper, gold, iron and aluminium = too soft for many uses. They are mixed with other similar metals to make them harder for everyday use. For example:
- brass, used in electrical fittings, is 70 percent copper and 30 percent zinc
- 18 carat gold, used in jewellery, is 75 percent gold and 25 percent copper and other metals
- duralumin, used in aircraft manufacture, is 96 percent aluminium and 4 percent copper and other metals.
Metals and their uses: Iron and Steel
Pure iron is soft because of it's atom arrangement - the atoms are all regularly arranged so they can slide over each other easily. However, pure iron is too soft to be used for many things.
Iron from the blast furnace is an alloy of about 96 percent iron, with carbon and some other impurities. It is hard, but too brittle for most uses, so most iron from the blast furnace is converted into steel by removing some of the carbon.
Carbon is removed from molten iron by blowing oxygen into it. The oxygen reacts with the carbon, producing carbon monoxide and carbon dioxide, which escape from the molten metal. Enough oxygen is used to achieve steel with the desired carbon content. Other metals are often added, such as vanadium and chromium, to produce alloys with properties suited to specific uses.
An iron alloyed with about 0.25 percent carbon makes low carbon steel, which can be used for car body panels as it is easily shaped. An iron alloyed with up to 2.5% carbon makes the hard, high-carbon steel - which is used for cutting tools.Stainless steel is iron alloyed with chronium and nickel. It is used for cutlery and sinks as it is resistant to corrosion.