Copper is mined in open pits and below ground. The ore usually contains less than 1% copper and is often associated with sulfide minerals. The ore is ground, concentrated, and slurred with water and chemical reagents. Air blown through the mixture attaches to the copper, causing it to float to the top of the slurry. The copper is then removed with a skimmer. The tailings remain and are dewatered and disposed of in tailing ponds. The water is recovered and recycled.
Extraction of copper using purification style.
The anode is a block of impure copper and cathode is a thin piece of pure copper.
When electricity is passed through the cell, copper is dissolved at the anode by oxidation, Cu2+ ions go into solution. (Cu(s) - 2e- Cu2+ (aq)).
At the cathode, copper is deposited by reduction. (Cu2+ (aq) + 2e- Cu(s))
As copper ions are transferred from the anode to the cathode, the anode gets smaller as the cathode gets bigger. This is a reaction. The concentration of the copper (II) sulfate remains unchanged. As copper is transferred from the anode to the cathode, soluble impurities dissolve in the copper (II) sulfate and are removed later. Insoluble impurities fall to the bottom of the cell
and collect as sludge. The sludge often contains precious metals (notably silver and platinum)
which are extracted and refined.
Extraction of plant in copper is removed from the solvent, cleaned in a flotation cell and a series of filters and pumped as near pure solution to a tank for ‘electro winning’. The copper solution acts as an electrolyte within cells containing stainless steel cathodes and lead alloy anodes. When current is added, copper metal is deposited on the cathodes whilst oxygen and acid is produced at the anodes.
After about seven days, the copper plates (now cathodes) are stripped from the steel cathodes and collected in three tonne bundles. These are shipped from the nearest port largely to Australian manufacturers for domestic use. The copper cathodes produced by electro winning contain 99.99% copper that is suitable for electrical uses.
Various methods of smelting can be used to convert the concentrates to copper metal. One method is to melt them with fluxes in a smelter furnace to produce copper matte, which is a mixture mainly of iron and copper sulphides usually containing 50% to 70% Cu. The molten matte is poured into a converter which contains more fluxes and converted into blister copper
This is about 99% pure. The blister copper is further refined in an anode furnace and finally electrolytically refined to pure cathode copper.
Uses of Copper and the Properties
Properties of copper
Copper is
1) An excellent conductor of electricity and heat.
2) Soft, easily bent and shaped.
3) Resistant to corrosion (very unreactive).
Uses
- Used for electrical wiring.
- Copper cookware which is not common.
- Gas pipes.
- Water pipes.
- It’s mixed with other metals to form alloys.
Aluminium
How Aluminium is extracted from the ground?
Aluminum ore is called bauxite. Bauxite contains aluminum oxide, water, iron oxide and other impurities. The purified dry ore, called alumina, is aluminum oxide - Al2O3.The alumina must be molten for electrolysis to occur, since the ions are not in the solid state. Unfortunately, alumina has a high melting point (2040 °C) and it is not practical to do electrolysis at this temperature. In the middle of the nineteenth century, it was found that alumina dissolved in cryolite.Cryolite is sodium aluminum fluoride - Na3AlF6.
Extraction of aluminum using electrolysis cell
Electrolysis of the alumina/cryolite solution gives aluminum at the cathode and oxygen at the anode. 4Al3+ + 12e- 4Al (aluminum metal at the (-) cathode). 6O2- - 12e- 3O2 (oxygen gas at the (+) anode). Aluminum is denser than the alumina/cryolite solution,
and so falls to the bottom of the cell where it can be tapped off as pure liquid metal.
The overall reaction is aluminum oxide aluminum + oxygen.
2Al23+O32-(l) 4Al (l) + 3O2(g)
Oxygen is discharged at the positive carbon (graphite) anode. Oxygen reacts with the carbon anode to form carbon dioxide gas. Carbon + oxygen carbon dioxide.
C(s) + O2(g) CO2(g)..
The carbon anode slowly disappears as carbon dioxide and needs to be replaced regularly.
Aluminum is the third richest element in the Earth's crust. It is the most abundant metal
but it is more expensive to produce than iron because of the cost of the large amounts of electricity needed for electrolysis, see Moles. Extracting aluminum from recycled scrap requires only about 5% of the energy needed to extract aluminum from its ore. Collecting scrap metal, and transport to the metal extraction plant add extra costs. Although being high in the series, aluminum is resistant to corrosion because of the thin layer of aluminum oxide (Al2O3)
which forms on its surface in air. The oxide layer protects the metal beneath and renders it inert to any further reaction. The thin oxide layer will react with an acid or alkali to form the corresponding aluminum salt + water. The exposed aluminum metal will then further react with or alkali to form the aluminum salt + hydrogen. For this reason, aluminum cookware should not be allowed to come into prolonged contact with citrus fruits or vinegar (acids), or alkali cleaners such as caustic soda (sodium hydroxide).
Properties and uses of Aluminium
Properties
1) is strong and has a low density.
2) is resistant to , and can be easily bent and shaped.
3) Is a good conductor of heat and electricity.
4) Can be polished to achieve a highly reflective surface.
Uses
-
Low density and strength which make it ideal for construction of aircraft, lightweight vehicles, and ladders. An alloy of aluminium called Duralumin is often used instead of pure aluminium because of its improved properties
(2) Easy to shape and corrosion resistance make it a good material for drink cans and roofing materials.
3) Low density makes it useable for greenhouses and window frames.
4) Good conduction of heat makes it useable for boilers, cookers and cookware.
5) Good conduction of electricity makes it use for overhead power cables hung from pylons
(low density gives it an advantage over copper).
6) High reflectivity makes it perfect for mirrors, reflectors and heat resistant clothing for fire fighting.
Bibliography
USEPA, Profile of the Nonferrous Metals Industry
GCSE CHEMISTRY (SECOND EDITIONS) b Earl and L D R Wilford
