Extraction of metals and Alloys Paper

Published: 2021-09-11 20:00:08
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An alloy is a mixture of metals, which may have different and improved qualities from metal elements, which make it. The percentage of elements in an alloy can be tailored to the application or purpose it is being made for. Usually an alloy is made of one metal (the base metal) with small amounts of other metals added. The other metals replace the position of the base metal in its structure.
Extraction of Metals
An element or a compound in nature inside the earth’s crust is called a mineral. They have a percentage of metal which can be extracted. This is called a metal ore. The most common metal ores are oxides and sulphides. Sulphides are the oldest ores. Oxides are formed when photosynthesis in plants release oxygen into the air. Metal ores are an infinite resource and once they are used, they are gone. Recycling helps this. Generally half of all metal is recycled through scrap metal facilities.
The Reactivity Series – (See appendix – diagram 1)
A metal that is under carbon in the Reactivity Series (zinc to silver) can be extracted from its ore by heating with carbon. Carbon is used as it is easily available and it’s cheap (coke and charcoal are both carbon). The metal is then reduced by the carbon. Hydrogen may be used to reduce other metals which are lower than it on the Reactivity Series. It is more expensive than carbon. It is only used for the extraction of tungsten. Gold and platinum are found naturally as elements and do not need to be reduced. Silver and copper are also naturally found.
Extraction of Metals and Alloying
Metal ores are found in the earth. They are rocks containing mineral or metal compounds or metals themselves and need to be extracted or removed from the rocks and the ground. To extract a metal from its ores you need to know its reactivity. The process involves a chemical reaction where the metal is separated from the other elements in the mineral.
History of Metal Extraction
Metals have been used by people for thousands of years. Gold and silver found in nature, were used for jewellery to show how wealthy people were. These two metals are too soft to be used as tools. The first useful metal discovered was bronze (the Bronze Age). Bronze was used a lot for tools and weapons in Asia and Africa from 4500 B.C. and in Britain from 2000 B.C. Bronze is not an element but an alloy of copper and tin. Ores of copper and tin can be reduced by heating with carbon. This would have happened as people lit wood fires in a place where tin and copper ore were. The burnt wood would have made the ores (copper and tin) into bronze.
After the Bronze Age, coal fires were used to produce enough temperature for the extraction of iron (hence the Iron Age) The Iron Age began in Asia and Africa in 1100 B.C and in Britain in 500 B.C. Metals above carbon in the reactivity series can only be extracted by electrolysis. With the discovery of electricity in the nineteenth century, this allowed the extraction of more reactive metals. Aluminium has been extracted since around 1870. (3000 years since they found iron and 6000 years since they found bronze).
Extraction of Aluminium
Aluminium is the third most abundant (plentiful) element in the Earth’s crust. It is more abundant and the more expensive to produce compared with iron. This is because it takes a lot of electricity for the extraction process of electrolysis to happen. Around half of aluminium used is recycled. It takes less energy to recycle aluminuim than to extract it from its ore. Handling costs of aluminuim in the recycling process adds to this. Aluminium is high in the Reactivity Series and is resistant to corrosion as a thin layer of aluminium oxide on its surface protects it from corroding.
Aluminuim has the ore called bauxite. Bauxite has aluminium oxide, water, iron and other things. The purified ore is called alumina (aluminium oxide). Alumina needs to be liquid or molten before the extraction method of electrolysis can happen. Alumina has a high melting point, so electrolysis cannot be done at this temperature. Alumina can dissolve in cryolite, which makes it have a lower melting point so electrolysis can be done at about 950oC.
The main alloy of aluminium is Duralumin. Aluminuim is also used in titanium alloys. Duralumin is an alloy of aluminuim (94%), copper (4%) and magnesium (1%). There may also be small quantities of manganese and silicon in the alloy. Duralumin is a low density alloy that has a greater strength to weight ratio than aluminium. Duralumin is used for aircraft construction.
Properties and Uses of Aluminuim
Aluminium is strong and has a low density. It is also resistant to corrosion and can be easily bent into any shape. Aluminium is a good conductor of heat and electricity. It can be polished to achieve a highly reflective surface.
Aluminuim can be used for making aircraft, lightweight vehicles, and ladders because it has a low density and it is strong. An alloy of aluminium, called Duralumin is used instead of pure aluminium because of its improved properties. Aluminium, as it is easy to shape and corrosion resistance, is a good material for making drink cans and roofing. It’s also used for greenhouses and window frames because of its low density and resistance to rust. Aluminium is a good conductor of heat, so it can be used for boilers, cookers and cookware. As it is a good conductor of electricity, it is used for power cables and wire. Aluminium is highly reflective so it’s used in mirrors, reflectors and heat resistant clothes for fire fighters to use.
Extracting Aluminium – (See appendix – diagram 2)
A steel container is coated with carbon – this is the negative electrode Electrolysis now begins. As aluminium is denser than the alumina and cryolite, it falls to the bottom where it is ‘tapped off’ as pure liquid metal. Oxygen is removed from the positive carbon electrodes. Oxygen reacts with the carbon to form make carbon dioxide.
Extraction of Iron
Iron is extracted from its ore in a Blast Furnace. The ore is called Haematite. This is iron oxide. The iron ore has impurities in it, usually silica. Limestone is added to the iron ore which reacts with the silica which forms molten calcium silicate in the blast furnace. The calcium silicate floats on the liquid iron. Iron is low in the Reactivity Series, so iron ore is reduced into iron metal by heating with coke.
How the Blast Furnace Works (See appendix – Diagram 3)
Hot air is blasted into the Blast Furnace which creates the carbon or coke to ignite. The temperature is about 2000oC. Carbon dioxide reacts with the carbon and makes carbon monoxide. This reduces iron in the ore into iron metal. Iron then drops to the bottom as liquid iron and is ‘tapped off’ as needed.
Properties and Uses of Iron
Iron is a magnetic metal. Iron from a Blast Furnace contains around 5% carbon which comes from the coke in the furnace. It is put into molds called pigs, and the iron is then called cast iron or pig iron. It is very brittle and cracks easily, but it has a good resistance to corrosion compared to pure iron or steel. Cast iron is used for manhole covers and for engine blocks for petrol and diesel engines. Carbon is removed from molten cast iron by bubbling air through it. The air reacts with the carbon before it reacts with the iron because it’s more reactive (the carbon). Pure iron with the carbon removed is called wrought iron. This metal is easily shaped and is used for ornamental metal work like gates. The iron in the Blast Furnace is made into steel for use in construction.
Alloys containing Iron
The iron alloys are steel, manganese steel and stainless steel. Steel is a fixture of iron and carbon. The percentage of carbon may vary from 0.1% to 1.5% giving steels different properties. Steel is inexpensive and strong and easily shaped. It can be used on the construction of bridges, buildings, ships and vehicles. More than half of the steel is recycled. Steel will need a protective coat, like paint or it will rust. Rusting reverses the process that happens in a Blast Furnace. Manganese steel is an alloy of iron. It’s iron (84%) and manganese (15%) and carbon (1%). It is very hard and is used for railway points and dredging equipment. Stainless steel is an alloy of iron. It is iron (80%) and chromium (15%), nickel (4%) and carbon (1%). Stainless steel is very strong, hard and resists corrosion. It is used in cookware, cutlery and industrial chemical plants.
Corrosion of Iron and Steel
When iron is exposed to air it will return to its oxide. This is called rusting or corroding. This process needs both oxygen and water, salt or acid will make corroding faster. You can prevent rust by coating the surface so the air doesn’t come into contact with it. It can also be protected by a more reactive metal (See the Reactivity Series in the appendix – diagram 1). Iron and steel are mostly protected by paint, plastic coating or metal plating. Zinc plating is called galvanizing. Chromium plating is used for wheels and bumpers of cars to give a polished surface. Sacrificial protection is used for ships, under water pipelines and oil rigs.
Extraction of Copper
Copper is sometimes found as a native metal. Copper ore can be reduced by causing it to react with carbon. The most common way is by heating copper sulphide ore which breaks down. The impure copper that results is called blister copper. Around half of all copper is recycled each year. Pure copper is needed for good electrical conductivity. Pure copper is made from the extraction method of electrolysis.
Extraction of Copper – Purification (see appendix – diagram 4)
The impure copper, when electricity is put through the cell, copper dissolves at the anode into solution. Copper forms at the cathode by reduction. Copper ions move from the anode to the cathode. The anode gets smaller and the cathode gets bigger. This is called the redox reaction. The impurities dissolve and fall to the bottom as sludge, which can have silver and platinum in it which can be taken out.
Properties and Uses of Copper
Copper is an excellent conductor of electricity and heat. It is soft and easy to shape. Copper is also corrosion resistant. It can be used for electrical wiring (so can aluminium) Copper is also used in cookware, but is not very common. It is used in gas pipes as it is easily bent for the application for it is ideal to use. Copper is used for water pipes for the same reason as why it is used for gas pipes. Copper is below hydrogen in the Reactivity Series (See the Reactivity Series in the appendix – diagram 1), so it does not react with water. Lead was always used in plumbing in the past, but is being replaced with copper because of the lead going into the water which is toxic. Copper is mixed with other metals to form alloys, mainly zinc for brass and tin for bronze.
Alloys containing copper include brass, bronze, cupro-nickel and duralumin. Brass is an alloy of copper (70%) and zinc is (30%). Brass is harder and less expensive than copper and can be used for musical instruments, screws and other fixtures or ornamental objects that need to be corrosion resistant. Bronze is an alloy of copper (90%) and tin (10%). Bronze is harder and stronger and rust resistant. Bronze is used for casting objects and bearings (e.g. wheel bearings). Cupro-nickel is an alloy of copper (70%) and nickel (30%). It is easily shaped and it is rust resistant and is used to make silver coins e.g. 5c, 10c, 20c, and the 50c pieces. Silver coins have not contained real silver since 1947.
Alloys containing Lead
The main alloy of lead is solder. Solder is an alloy of lead (70%) and tin (30%). Half of the lead and tin used each year is recycled. Solder has a low melting point and is stronger than lead or tin. Solder is used for connections in electrical wiring and plumbing.
Properties and Uses of Lead
People have used lead as long ago as 5000B.C. Lead is a shiny metal that is corrosion resistant and very dense and soft. It is toxic if absorbed by the body. Lead is rarely found in nature and it is a heavy metal. It has a low melting point and is flexible. It conducts electricity.
Lead is able to be shaped into many things from water pipes to coins and stained glass windows. It also is used in car batteries and TV’s and computers. It is also used for making wheelchairs, lift trucks, baggage loaders, golf carts and submarines. Lead is also used to absorb radiation around x-rays and nuclear equipment. It’s also used in computer screens to again absorb radiation. It also absorbs sound. Leads used as a shield around electrical cables.
Alloys of Titanium
Titanium is mixed with aluminium (5%) and vanadium (5%). Titanium is expensive and is only used where its properties are needed. Its properties are its low density, hardness and rust resistance. Titanium alloys are used in special parts of aircraft and ship construction and chemical plants and hip joint replacements.
The mined minerals are sent to mills to be separated from one another using electrical and magnetic techniques. To obtain pure, white titanium dioxide, the minerals are reacted with chlorine then burned in oxygen. Producing pure titanium metal is only done overseas, where mineral sands are reacted with other chemicals and then heated
Properties and Uses of Titanium
Titanium is a newish metal which started to be commercially produced in the 1940’s. It is lightweight, strong and rust resistant. Titanium is a silver – white metal and is soft when alloyed with other metals. It has a high melting point. It is non toxic and has many uses.
Titanium is used to make aircraft engines, spacecraft, missiles, cars, sports equipment, watches, and general industrial equipment. Being non-toxic, it can be used for pacemakers, artificial joints and bone pins.
Alloys and Recent Developments
In recent times, the development of alloys has flourished because of further research and development of metals and characterising metals and the implementation of new materials and processes. Using previous philosophy of how metals are extracted and alloyed and advancing on these techniques which include using the modern ‘top-down’ method that eliminates design constraints in the earlier manufacturing process.
The discovery of high strength steels for new applications is a recent development. This means that the steels are stronger, tougher and even have a higher rust resistance when alloyed. New alloys of stainless steel have also been developed and the metal can now be used for new applications previously unavailable, especially in aviation.
High temperature metallic materials can now be used in casting alloys in the ‘wrought’ processing of alloy sheet technology. Also new super-alloys are being produced that can take higher temperatures using new chemistry processes.
Alloys have in recent times needed to be lighter and also retain their strength for use in modern applications. Another recent development is the production of alloys is called Al-Li, which has great corrosion prevention compounds. Researchers are now developing fatigue resistant alloys to reduce failures of components and less maintenance.
Lastly, low cost methods have been found, including single hearth melt, laser deposition and casting for titanium alloying has been discovered.

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