GCSE OCR Gateway Chemistry C6.1a Extracting copper from its ore using carbon reduction

GCSE OCR Gateway Chemistry C6.1a

C6.1a To be able to explain, using the position of carbon in the reactivity series, the principles of industrial processes used to extract metals, including extraction of a non-ferrous metal

Extraction of copper by heating copper oxide with carbon

Extracting copper from its ore using carbon reduction

Carbon lies midway in the reactivity series.  Its position is above iron but below zinc:

Reactivity series of metals

Sodium Na

Lithium Li

Calcium Ca

Magnesium Mg

Aluminium Al

Zinc Zn

CARBON C

Iron Fe

Lead Pb

CopperCu

The implication of carbon’s position in the reactivity series is that is can reduce the oxides of metals below it i.e. iron oxide lead oxide and copper oxide

Carbon has for centuries been used to extract iron from its ferric ores.  It is also used to extract copper from its sulphide ores.

The Earth’s crust is thought to contain around 33ppm copper but for a copper ore bed to be economic to extract, it must contain over 0.5% copper and preferably 2% or more copper.

Known reserves of high–grade ore amount to around 1 billion tonnes copper.  Sounds a lot but if the present rate of copper extraction is 12.5 million tonnes per annum that gives us about 65–75 years worth of copper left in the earth as far as we know!! 

Hence the importance of recycling copper scrap, searching for new ore beds and the economical use of the metal in order to conserve these resources of copper.

The major ore is copper sulphide (CuS).  Copper is extracted from this ore by smelting with carbon (added as hydrocarbon fuel oil) and this gives a 98+% pure metal called blister copper. 

CuS     +    C    +     2O₂     ⟶       Cu        +         SO₂       +       CO₂

Blister copper is further heated and refined to produce thick sheets called anodes for electrolysis.

The sulphur dioxide is collected and used in the production of sulphuric acid. 

This outlines shows the processes followed in copper production:

The extraction of copper from malachite using carbon

You need to be familiar with an experimental method to illustrate the extraction of copper from an ore.

In this example I am going to give, copper is extracted from its ore: malachite basic copper carbonate (CuCO₃.Cu(OH)₂). 

Malachite is a copper ore consisting of mainly basic copper carbonate (CuCO₃. Cu(OH)₂) .  This experiment involves producing copper from copper (II) carbonate.  The copper carbonate is first heated to produce copper(II) oxide (CuO) which is then reduced to copper using carbon as a reductant.

Procedure

Several spatula measures of powered green malachite copper(II)carbonate are placed on a tin lid and mixed with several spatula measures of black powdered charcoal.

 The pile is then covered with a thin layer of charcoal.

The mixture is strongly heated on the tin lid for a very short time say 2minutes — no longer.  Watch for a red glow passing through the contents on the lid.

Now add the contents of the lid very quickly and carefully into 400ml of cold water in a 600ml beaker.  Swirl the beaker contents so that the brown copper sinks to the bottom of the beaker.  Then pour off the water and charcoal suspension.  Add water swirl and pour off the charcoal suspension until you are left with a fairly clean brown precipitate on the bottom of the beaker.  This brown solid should be copper —but is it?

Here’s how to test it to see if its copper.

Obtain another beaker and put a few copper turnings in it, then in a fume cupboard add a few drops concentrated nitric acid.  If its copper you’ll see dense brown fumes form immediately of nitrogen(IV)oxide.  Now if the brown solid is also copper the same thing should happen: brown fumes with the concentrated nitric acid. 

Analysis

The thin layer of carbon prevents air oxidation of any hot copper products.

Thermal decomposition of copper carbonate occurs first on heating the mixture.

CuCO₃             ⟶      CuO   +   CO₂

Green                          black

Then the excess carbon reduces copper oxide to copper

2CuO     +     C       ⟶          2Cu      +      CO2

This second reaction is a redox reaction since the copper loses oxygen: its reduced, and the carbon is oxidised: it gains oxygen.

Copper made by this process of carbon reduction is not really pure enough for many electrical applications and uses so another technique has to be found to further refine the copper to a level of purity suitable for electrical wiring and other uses .i.e from 99.5% to 99.9995% purity.