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Copper Poduction

Written on December 19, 2016   By   in Uncategorized

Copper
This report will explain how the metal element copper is separated and refined from its ore and also discuss technological advances in chemistry, as well as the economical efficiency and consequences of the production of copper.
Copper is found naturally in rocks in the crust of the Earth. The crust contains rocks, which are mixtures of solidified mineral crystals and grains. In these minerals are materials with specific chemical compositions and unique physical properties. If a rock has enough of a metal in it to be economically viable to extract then it is called an ore. Here is a table containing the main copper ores:
Mineral name | Formula | Appearance |
Cupritecopper oxide | Cu2O | Red, earthy |
ChalcociteCopper(I)sulphide | Cu2S | Dark grey, metallic |
BorniteCopper iron sulphide | Cu5FeS4 | Golden brown, metallic |
MalachiteCopper carbonate hydroxide | CuCO3Cu(OH)4 | Bright green, earthy |
AzuriteCopper carbonate hydroxide | 2CuCO3Cu(OH)4 | Blue, glassy |
ChalcopyriteCopper iron sulphide | CuFeS2 | Golden yellow, metallic |

As you can see, all of the ores contain the element copper (Cu) and these atoms are bonded with other elements and/or compounds such as oxygen (O), sulphur (S), Iron (Fe), carbonate (CO3) and hydroxide (OH) to form a crystalline solid. These compounds containing copper are found in ores which also contain impurities like sand (SiO2) and other useless rocks such as halite (NaCl).
In Queenstown, Tasmania, a mine in Mount Lyell extracts copper. The main form of copper found at this mine is chalcopyrite (CuFeS2). This tetragonal crystal is made of copper (I), iron (II) and sulphur.
Below is a list of the properties of chalcopyrite and the elements in it.
Properties of chalcopyrite:
Lustre: | Metallic |
Transparency: | Opaque |
Colour: | Brass yellow, often with an shining tarnish. |
Streak colour: | Greenish black |
Tenacity: | Brittle |
shape: | Irregular/Uneven |
Density | 4.1 – 4.3 g/cm3 |
Structure: | Tetragonal crystal system |
Additional properties: | Tend to cling to bubbles in water due to hydrophobia |Elements in chalcopyrite:
Copper
* Lustrous (shiny)
* Hard
* High density
* High tensile strength
* High melting and boiling points
* Good conductors of heat and electricity
* Malleable
* Electron configuration in chalcopyrite has one electron in the outer shell so it has 1+ chargeSulphur
* Dull yellow colour
* Soft
* Low density
* Low melting and boiling point
* Bad conductor of electricity
* Brittle
* Electron configuration of 2,8,6 so has a 2- charge
* Low densityIron
* Lustrous (shiny)
* Hard
* High density
* High tensile strength
* High melting and boiling points
* Good conductors of heat and electricity
* Malleable
* Electron configuration has two electrons in the outer shell in chalcopyrite. Has a 2+ charge
Separation processCrushing and grinding
Firstly the rock in the mine must be broken. A churn drill is the first step in this process which bores down into the rock with a hard steel bit. The churn drill holes are loaded with explosives which blow the rock into pieces. The ore is then transported to the crushing plant. In here, the rocks are crushed into particles of less than 10mm in diameter. This assists in the separating of the copper minerals as they are found as fine grains in the ore. After being passed through the several crushing plants, the copper ore emerges as a fine powder.Concentration
Now that we have obtained a fine powder of chalcopyrite and other useless rock material, it is time to separate the useful compound from the gangue or waste rock. This is done using a method called froth flotation. This is a method used to separate sulphide minerals from gangue due to sulphides hydrophobic properties. Copper iron sulphide is hydrophobic as both its sides are positive since they are copper and iron. Since water has a positive side and a negative side (hydrogen??™s are on one side and oxygen on other) the chalcopyrite repels the water.

Non-polar molecule Polar molecule
– +
Cu
Fe
O
H
S
+ + –
+ + –
H
+ + –
+ – + +Positive charges repel each other, making chalcopyrite hydrophobic.(Number of positive/negative
charges aren??™t to scale)
This means that minerals with positive charges around them like sulphide are repelled from water, and since the air bubbles do not have any water in them they attach to them. The frothing agent used may also contain oils as the hydrophobic sulphide minerals are also attracted to them. Since oils and air (mainly nitrogen and oxygen) are less dense than water, the bubbles and sulphur minerals floats.
After the copper mineral has floated to the top of the mixture, it is skimmed off and gets dried which removes the water and frothing chemicals. Now we have obtained copper concentrate. This means that the copper mineral is concentrated (about 20%) as we have removed the gangue and unwanted rock.
The gangue which settles at the bottom of the cell is taken out of the cell from an outlet tap. These waste rocks are then used to refill used mines or stored in a tailings damn. The water used in this process is re-used as much as possible to increase economical efficiency and reduce water consumption.Extraction
Subsequently, the copper is extracted from the compound it is found in. This is the compound we have just concentrated: CuFeS2 (Chalcopyrite). This is done by the process of smelting. Smelting is a chemical process used to isolate an? element? from its ore using? heat? and a reduction agent. In the smelting of copper iron sulphide, sand (SiO2) is used as a reduction agent and coal is added for heat. These are all mixed in a furnace and heated to very high temperatures with the presence of oxygen. This separates the iron from the chalcopyrite. In the smelter, iron oxide formed from the combustion of copper iron sulphide reacts with the silicon dioxide. This leaves only three products in the smelter: copper (I) sulphide, iron silicon trioxide and sulphur dioxide (escapes from the top as a gas).
Below are the chemicals equations for this process.
2CuFeS2(s) + 4O2(g) Cu2S(l) + 2FeO(s) + 3SO2(g)
Copper iron sulphide + oxygen copper sulphide + iron oxide + sulphur dioxide

FeO + SiO2 FeSiO3
Iron oxide + silicon dioxide iron silicon trioxide

As we can see, the copper(I) ion forms an ionic bond with the sulphur to make Cu2S . This is because copper(I) has a charge of +1 since it has one electron in its outer shell. Although the sulphur has six electrons in its outer shell so it needs two more electrons to have a full, stable outer shell. It achieves this by bonding with two copper(I) ions. The iron (II) ions have two electrons in their outer shell so they have a 2+ charge as they must get rid of two electrons to become stable. Since the oxygen has an electron configuration of 2, 6 it needs two more electrons to be stable. It takes the two electrons from the iron and they bond ionically due to the electrostatic forces of attraction between opposite ions. Another sulphur atom from the chalcopyrite reacts with oxygen making a covalent bond which forms 3SO2. This is done as the oxygen and sulphur both share two electrons (since both need two more electrons) giving them a stable outer shell.
The iron oxide compound produced reacts with silicon dioxide to make iron silicon trioxide. Oxygen has 6 electrons in its outer shell and silicon has 4. They bond covalently like this:

This leaves this anion with a -2 charge. However iron (II) has a 2+ charge so it ionically bonds with them (due to electrostatic forces of attraction between oppositely charged ions) to form iron silicon trioxide.

The copper sulphide formed is then taken to the converter furnace where it is heated with oxygen to extract copper from copper sulphide. Sand is added in the converter to remove any leftover iron oxide.
Converter:
Cu2S(s) + O2(g) 2Cu(l) + SO2(g)
Copper(I) sulphide + oxygen copper + sulphur dioxide

FeO(s) + SiO2(s) FeSiO3
Iron oxide + silicon dioxide iron silicon trioxide

Overall the reaction is:
2CuFeS2(s) + 5O2(g) 2Cu(l) + 2FeO(s) + 4SO2(g)

When copper(I) sulphide reacts with oxygen, sulphur and oxygen both share one electron with each other and the oxygen atoms share one electron with each other to form a stable covalent compound of sulphur dioxide. The copper atoms left form a metallic bond with each other which consists of many positive nucleuses of copper atoms with a delocalised sea of electrons surrounding them, which are free to move around.

The molten slag (FeSiO3, gangue, fluxes and some copper) falls on top of the molten copper (since it is less dense than copper). This slag is then tapped off the top and undergoes the process of grinding and froth flotation again to extract more copper.
Sulphur dioxide gas escapes the top of the smelter and is used to make sulphuric acid. This is done by reacting it with oxygen to obtain sulphur trioxide then it is dissolved in water to make sulphuric acid.
2SO2(g) +O2(g) 2SO3(g)
SO3(g) + H2O(l) H2SO4(aq)
In this reaction, the covalent compound sulphur trioxide is covalently bonded by sharing two electrons with one oxygen atom and one oxygen atom sharing two electrons with the sulphur atom. The sulphur atom then shares two of its remaining for electrons with each oxygen atom.

(Sulphur trioxide)

Sulphur trioxide then reacts with oxygen ions in water to form sulphate ion with a -2 charge as sulphur tetraoxide has two more electrons than protons. This anion is attracted to the two hydrogen atoms which have a charge of 1+ each due to the electrostatic forces of attraction between oppositely charged ions. They then form an ionic bond of H2SO4.
As copper is denser than the slag it sinks to the bottom of the mixture in the furnace, from where it is tapped off. The separation process gives copper which is 98% pure although other impurities such as sulphur, gold and silver are left in the copper. This copper is called blister copper as bubbles of SO2 escaping from the copper look like blisters.
However even though we have separated the copper, we must purify it to make it suitable for uses such as electrical wiring. This is done by electrolysis. The impure copper (from separation) is used as the anode, and the cathode is made of a steel slab covered in pure copper. Numerous anodes and cathodes are placed alternatively in a tank which contains an electrolyte. When electricity is run through this electrolyte, the impure copper metal becomes copper ions, which are attracted to the negative cathode. As they deposit, pure copper builds on the cathode while impurities such as silver and gold fall to the bottom.

Impact of technological advances on the understanding of chemistry
Through the many thousands of years man has always been discovering new metals, new ways to extract them and new uses for them. The discovery of these metals has greatly influenced our understanding of chemistry.
The first type of material used by man was simply stones. These would serve for purposes such as weapons and tools. This era in time was called the ???stone age???. This simply taught man that different objects have different properties for example stone is harder than wood.
Many years later man began finding metal nuggets on the ground. These metals were copper, gold and silver due to their un-reactive properties. These metals were simply hammered into shape to serve whatever purpose they needed to. Man learnt that metals could be hammered into shape.
Around 6000 B.C copper was extracted by its ore which lead to the copper age. Copper ore and charcoal heated together produced a high-carbon, low-oxygen atmosphere which smelted the ore. This taught man that you could extract a metal from its ore by smelting it (heating with carbon). Copper was less brittle than stone and was malleable. It could also be hammered to be made harder. This served as a material for weapons such as swords and tools such as pots.
3000 years later, copper and tin had been alloyed together introducing the Bronze Age. Bronze was harder and had a lower melting point so it was a lot more useful than copper which allowed it to be shaped easier. Through the mixing of these two metals, man had learnt how the properties of a material change by adding different chemicals. When two different elements are added together, they become harder as the atoms cannot slide over each other. Furthermore alloying metals disrupts their sea of electrons which holds them together, this then lowers their melting points.
The discovery of more metals such as lead and zinc, helped broaden our knowledge on metals as we learnt about their individual properties and what they could be used for. Since lead was un-reactive in was used in plumbing and zinc was used by alloying with copper to make brass, a mixture harder than copper. By discovering more metals, man learnt about the properties of metals and that every metal has unique properties which are useful for different purposes.
New techniques to extract metals were used which lead to the discovery of more metal elements. Iron was discovered by using a furnace with charcoal and an oxygen supply which allowed higher temperatures to be reached. Once again, man discovered another element with unique properties. Steel was also discovered by heating iron with carbon and quenching it with water. Steel was a lot harder than iron and less brittle. These technological advancements showed man that to extract different metals, different temperatures are required. Additionally man learnt that the method in which an alloy is made affects its properties.
Although man discovered many new metals and made use of them, some issues had been raised. Firstly, extraction of metals creates a lot of pollution as carbon dioxide and sulphur dioxide are released during smelting and by machinery used in the extraction process. This has damaged our environment. Some of the Earth??™s resources have been nearly depleted due to our extensive use of metals. This increases prices and may result in a deficiency of metals for future generations. Since metals are less concentrated in the Earth, this makes it harder to extract metal, which means more money and time is required. Lastly lots of money and time has been put into the advancement of our understanding in chemistry. This could have been put in other areas such as medicines which may have lead to more advantages for society.
All the technological advancements such as the discovery of smelting have allowed us to obtain an extensive knowledge on metals and their purposes. Without this vital knowledge, humanity would never have developed to the stage it is at now. Even though metals may have costed a lot of money and depleted the Earth??™s resources, they definitely contribute to a huge role in the evolution of humanity.
Economical efficiency
Difficulty and cost of extraction
Since copper is not very reactive, it is less energy consuming to extract it from its ore as the energy required to break weak bonds between atoms is less than stronger bonds. This means copper can be extracted at relatively low temperatures so copper is easy and cheap to extract.
Abundance of ores and the concentration of metals in the ores
Copper is a very scarce element, only making up 0.07% of the crust. Unfortunately Mt Lyell has one of the lowest percentages of copper in its crust ??“ only about 0.4%. This means that a lot of energy and therefore money must be put in to extract the copper as a lot of the ore is gone to waste. This increases prices of copper.
Location of ores and cost of transport
In Mt Lyell, the mine is very close to the extraction plant which lowers costs of transport as less fuel is required. However the fact that Tasmania is an island means that it must export its ores to other countries. The price of this shipping greatly reduces economical efficiency. Additionally there is a delay in time for the copper to arrive to other countries.
Recycling
The recycling of copper greatly reduces the energy used. Only 6% of the energy required to obtain copper form its ore is needed to recycle it. Since copper is relatively un-reactive, the recycling process is also made a lot easier and it doesn??™t corrode which means more of the copper can be extracted from recycling. Currently not much copper is recycled, although as people are beginning to realise the advantages of recycling, more recycling plants are being made.
Overall the process of extraction of copper from Mt Lyell is not efficient as the ore is very scarce at that location, the costs of exporting ores is very high and not much copper ore is being currently recycled. However cheaper and easier techniques such as bioleaching and phytomining are beginning to be used which are more efficient. New fuels may be used in the future which will reduce costs of transport. New areas rich in copper may also be utilised and recycling is currently increasing, making the best of the Earth??™s resources.
Consequences of copper mining on the environment
The mining of copper used to leave huge scars on the face of the Earth. Huge piles of waste rock were also dumped near the quarry. These scars and wastes were eyesore and ruined the areas view. Waste rocks dumped next to rivers and lakes also used to intoxicate the water as heavy metals leached into it. Now mines are filled up with any waste rock after they are used and vegetation is replanted to encourage wildlife.
Sulphur dioxide released severely damages the environment as it reacts with water in rain to form acid rain. This kills plants and ruins the soils PH levels leaving the affected area barren. Acid rain also damages buildings made of limestone as it corrodes it. If the sulphur dioxide dissolves in rivers, fish and aquatic life may be killed. Sulphur dioxide emissions are reduced by passing SO2 through scrubbers which dissolve the sulphur dioxide in water. This then produces sulphuric acid, stoping SO from escaping into the atmosphere.
Huge amounts of water are used in the extraction of copper during operations such as froth flotation and washing. Water may also get contaminated which kills wildlife and poisons water. To reduce these consequences, as much water as possible is recycled and water which is contaminated is kept in retention ponds.

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