The earth's crust contains many naturally occuring elements & compounds called minerals.
A metal ore is a mineral that contains enough metal to make it economically viable to extract it. Over time it may become more or less economic to extract a metal from an ore as technology develops.
Ores are mined and impurities may be removed before the metal is extracted & purified.
This mining can involve the digging up & processing of large amounts of rock.
Extracting metals from their ores
The method of metal extraction depends on how reactive the metal is.
Unreactive metals like gold, exist naturally in the earth and can be obtained through panning. But most metals are found as metal oxides, or as compounds that can be easily changed into a metal oxide.
Metals that are less reactive than carbon can be extracted from their oxides by heating with carbon.
Metals more reactive than carbon are extracted by electrolysis of molten compounds.
Extraction of copper
Copper useful - good conductor of electricity & heat, easily bent into shape, hard enough to be used to make water pipes & tanks. Doesn't react with water - lasts a long time
Copper can be extracted from copper-rich ores by heating ores in a furnace - smelting. Can then be purified by electrolysis, can also be obtained from solutions of copper salts by electrolysis or by displlacement using scrap iron During electrolysis positive copper ions move towards negative electrode & form pure copper metal. Mining of copper means running out of copper rich ores. New methods have to be developed to extract copper from ores that contain less copper.
Copper can be extracted from:
-Low grade ores
-Contaminated land by phytomining or by bioleaching.
Phytomining is method that uses plants to absorb copper. As plants grow they absorb and store copper. Plants then burned and ash produced contains copper
Bioleaching uses bacteria to extract metals from low grade ores. Solution containing bacteria is mixed with a low grade ore. Bacteria convert the copper into solution where it can be easily extracted
Iron oxide can be reduced in a blast furnace to produce iron. Molten iron obtained from a blast furnace contains roughly
- 96% iron
- 4% carbon and other metals
The Iron brittle because its impure, has limited uses. Iron to be produced - imourities have to be removed.
Atoms in pure iron are arranged in layers that can slide over each other easily - pure iron soft and malleable. Can be easily shaped, too soft for many practical uses. Properties of iron can be changed by mixing it with small quantities of carbon or other metals to make steel. Majority of iron is converted into steel. Steel is an alloy
Many of the metals you come across every day are alloys. Pure copper, gold and aliminum are too soft for many uses, so they are mixed with small amounts of similar metals to make them harder for items in every day use.
Carbon is added to iron to make the alloy steel.
Alloys like steel are developed to have the neccessary properties for a specific purpose.
In steel, the amount of carbon and / or other elements determines its properties:
- Steel with a high carbon content is hard and strong
- Steel with a low carbon content is soft and easily shaped
- Stainless steel is hard and resistant to erosion
The transition metals
Between groups 2 and 3 in the Periodic Table is a block of metallic elements called the transition metals.
The transition metals:
- are good conductors of heat and electricity
- are hard and mechanically strong
- have high melting points
- can be bent or hammered into shape
The properties make the transition metals very useful as strucural materials, and as electrical and thermal conductors.
Titanium & aliminium are extracted from their ores by electrolysis. Electrolysis has many stages and requires a lot of energy - expensive process.
Copper is useful for chemical wiring & plumbing
Aliminium - resistant to corrosion & low density, so very light
Aliminium used for - drinks cans, window frames, lightweight vehicles & aeroplanes.
Titanium - strong & resistant to corrosion. Used in aeroplanes, nuclear reactors & replacement hip joints