7.1 Copper
🎯 Learning Outcomes
After completion of the chapter, students should be able to:
- Describe the occurrence and important ores of copper
- Explain the main steps in the extraction of copper from copper pyrites
- Describe properties (reaction with air, acids, aqueous ammonia, and metal ions) of copper
- List the important uses of copper
- Explain the chemistry (preparation, properties, and uses) of blue vitriol
- State the formula and uses of red and black oxide of copper
1 Copper — Occurrence & Ores
Occurrence
Copper occurs both in native (free) and combined forms.
- Found naturally in countries like Chile, USA, Russia, China, and Zambia
- Present in trace amounts in plants and animals
- In Nepal, copper deposits are found in many regions and have been used since ancient times
It has been found in deposits in about 107 localities.
Ores of Copper
Copper mainly occurs in the ores listed below.
| Ore | Formula |
|---|---|
| Copper pyrites or chalcopyrites | CuFeS₂ |
| Cuprite or ruby ore | Cu₂O |
| Copper glance or chalcocite | Cu₂S |
| Malachite (green) | Cu(OH)₂·CuCO₃ |
| Azurite (blue) | 2CuCO₃·Cu(OH)₂ |
| Tenorite | CuO |
| Bornite | 2Cu₂S·CuS·FeS |
2 Extraction — Crushing to Roasting
The extraction of Cu metal from copper pyrites, CuFeS₂, involves several steps.
The ore is first crushed in large jaw crushers and finely ground in ball mills.
- Removes impurities (gangue) from ore.
- Gangue — unwanted material, such as sand or rock, that surrounds and mixes with the valuable mineral in an ore deposit.
- The Froth Flotation Process concentrates the sulfide ores:
- A suspension is created in water with the powdered ore, and pine or eucalyptus oil is added.
- The suspension is stirred by a constant blast of compressed air.
- The oil (froth) wets the metal sulfide, and the water wets the gangue.
- This frothy metal sulfide ore is skimmed off from the top.
- The gangue particles remain at the bottom and are removed.
- Thus, the copper content of the ore is increased to 25–30%.
- The concentrated ore is heated strongly in a current of air on the hearth of a reverberatory furnace.
- The process removes arsenic and antimony impurities as their volatile oxides.
- The pyrite ore is converted into a mixture of cuprous sulfide, iron sulfide and ferrous oxide.
3 Extraction — Smelting, Bessemerisation & Refining
The roasted ore is mixed with sand and coke in a water-jacketed blast furnace. It is made of sheet steel and lined inside with firebricks. A blast of air enters from the lower part of the furnace to combust coke.
The oxidation of FeS, which already started in the roasting step, goes on further. The ferrous oxide formed combines with sand (SiO₂) to give easily fusible silicate slag. The copper oxide is also converted into sulfide.
The molten mass below the slag consists of a mixture of sulfides of copper and iron, along with SiO₂, which is known as Matte or Coarse Metal. The slag is removed/runoff, and matte is poured into water, where it is obtained as granules. It consists of about 50% Cu.
The molten matte with little silica is run into a Bessemer converter, and a blast of air is passed in. Iron present in the matte is first oxidised into ferrous oxide, which combines with silica to give slag.
The slag is removed, and the blast is continued; self-reduction of oxide and sulfide occurs. Cu₂S is then oxidised to Cu₂O, and when two-thirds of it is oxidised, the oxide of copper reacts with the remaining Cu₂S to give elemental copper and sulphur dioxide. The slag is removed, the blast of air is stopped, the converter is tilted, and blister copper is taken out.
The molten mass is allowed to cool, and it slowly releases the dissolved SO₂ gas as bubbles. This gives the shapes of blisters to the surface of the solidified Cu, hence called blister copper. Blister copper is ~98%–99% pure.
Blister copper is refined mainly by the following two methods:
Furnace / Thermal Refining
The blister copper, containing impurities such as Fe, S, As, and Pb, is melted in a reverberatory furnace provided with a silica lining, and air is blown in.
- Oxides of Pb, S, Zn, As, Sb, etc., formed, being volatile, escape.
- The non-volatile oxides of Mn, Fe, Co, Ni, Bi, etc., form slag with silica.
- The slag is removed. The remaining molten mass consists mainly of copper with some copper oxide.
- It is stirred with a pole of green wood (Poling) to reduce the copper oxide to copper (nearly 99.5% pure).
Electro-refining of Copper
An impure copper block is made the anode, and a thin sheet of pure copper is made the cathode in an acidified CuSO₄ solution.
- When an electric current is passed, the Cu²⁺ ions get reduced and deposit on the cathode as copper.
- The copper anode is oxidised to Cu²⁺ ions and dissolves in solution.
- The impurities present in the impure copper anode settle at the bottom as anode mud.
- Nearly 99.9% pure copper metal is obtained.
4 Properties of Copper
1. Action of Air
Copper is not affected by dry air at ordinary temperature, but it slowly converts into green basic carbonate in moist air and in the presence of CO₂.
When copper is heated in air below 1100°C, black oxide of copper is formed.
But above 1100°C, red oxide of copper is formed.
2. Action with Acid
With HCl: Copper does not react with dilute HCl under ordinary conditions. In the presence of oxygen, copper can slowly dissolve in warm hydrochloric acid.
With H₂SO₄: Copper does not react with cold dilute H₂SO₄ under ordinary conditions. It reacts with warm dilute H₂SO₄ in the presence of air.
On heating with concentrated H₂SO₄, SO₂ gas is produced.
With HNO₃: Copper reacts with different concentrations of HNO₃, evolving different gases like N₂, NO₂, NO, and N₂O.
3. Action of Ammonia
Copper dissolves in ammonia solution in the presence of oxygen.
4. Action with Metal Ions (Copper as reductant)
Copper acts as a reducing agent and displaces less electropositive metals Ag, Pt, and Au from their water-soluble salts.
5 Uses of Copper & Alloys
Uses of Copper
- As conducting wires and cables.
- Electronics industry — used in printed circuit boards (PCBs), microchips, motors, transformers, and electronic components.
- To form alloys like brass, bronze, etc., used in machinery parts, tools, and utensils.
- Containers and utensils.
- Coins of currency (historical use).
- Electroplating.
- Salts of Cu are used in agriculture as insecticides and pesticides.
- To prepare copper sulfate.
Some Alloys of Copper
| Alloy | Composition |
|---|---|
| Brass | Cu 60–80% + Zn 20–40% |
| Bronze | Cu 88% + Sn 12% |
| Bell metal | Cu 80% + Sn 20% |
| Gun metal | Cu 88% + Sn 10% + Zn 1% + Pb 1% |
| German Silver | Cu 56% + Zn 24% + Ni 20% |
6 Blue Vitriol (CuSO₄·5H₂O)
It is commonly known as “नीलो तुथो” in Nepali.
Preparation
1) In the laboratory, copper sulfate is prepared by the action of dilute sulphuric acid on cupric oxide CuO, cupric hydroxide Cu(OH)₂, or basic carbonate CuCO₃·Cu(OH)₂.
On the commercial scale, it is produced by the action of dilute H₂SO₄ on copper in the presence of air.
Properties of Blue Vitriol
- A blue crystalline solid.
- Readily soluble in water, insoluble in alcohol.
Action of Heat
When this anhydrous salt comes in contact with water, it turns blue.
Further heating decomposes the anhydrous salt (white) into black oxide of copper and sulphur trioxide.
Action with Ammonia
When copper sulfate is treated with ammonia, a bluish-white precipitate of Cu(OH)₂ is seen. On adding excess ammonia, a deep blue colouration of the tetramine cupric sulphate complex is formed.
You must have seen such a colour change during the confirmatory test of Cu²⁺ basic radical.
Action with Potassium Iodide
When copper sulfate is treated with potassium iodide, dark brown iodine is precipitated.
Action with Potassium Ferrocyanide Solution
When a copper sulfate solution is treated with potassium ferrocyanide, a chocolate-brown precipitate of cupric ferrocyanide forms.
Uses of Blue Vitriol
- Insecticides and fungicides in agriculture.
- Electrolyte solution in electroplating.
- Mordant in dyeing and calico printing.
- Preservative for timber.
7 Oxides of Copper
Black Oxide of Copper (CuO, cupric oxide)
Uses
- Glass and ceramics industry — used as a black/blue-green pigment in glass, enamel, and ceramic glazes.
- Manufacture of copper salts — used as a raw material to produce compounds like copper sulfate (CuSO₄).
- Catalyst in industries — used in oxidation reactions and some gas purification processes.
- Battery and electronics industry — used in dry cells and certain electronic materials.
Red Oxide of Copper (Cu₂O, cuprous oxide)
Uses
- Antifouling paints (marine industry) — used in paints for ship bottoms to prevent the growth of algae, barnacles, and other marine organisms.
- Glass and ceramic industry — used as a red pigment to produce red, ruby, or reddish-brown colours.
- Manufacture of copper salts and chemicals.
- Agriculture (fungicide) — used to control fungal diseases in crops (especially in seed treatment and crop protection).
📘 Chapter Summary
- Copper is an important transition metal widely used in industry.
- Extracted mainly from chalcopyrite through roasting, smelting, and refining.
- Forms important compounds like CuSO₄·5H₂O.
- Shows characteristic blue complex formation with ammonia.
- Used extensively due to its conductivity, durability, and alloy-forming ability.