Heavy Metals- Copper

Heavy metals

The metals having relatively high density i.e. greater than 5 gm/cc are called heavy metals. These are iron, copper, silver, gold, mercury, lead, zinc, iridium.

Copper

Ores of copper

1. Copperpyrite or chalcopyrite: CuFeS₂
2. Copper glance: Cu₂S
3. Cuprite: Cu₂O
4. Malachite: CuCO₃.Cu(OH)₂
5. Azurite: 2CuCO₃.Cu(OH)₂

Extraction of copper from copper pyrite

1. Crushing and pulverization

Big lumps of ores are crushed using jaw crushers to get crushed ore which is pulverized using a pulverizer or stamp mill to get powdered ore.

2. Concentration by froth floatation process

The powdered ore is taken in a tank containing water and a small amount of pine oil. The mixture is heated by the blast of air. Impurities are wetted by water and get collected at the bottom of the tank. Ore particles are wetted by oil and come to the surface as froth. The froth is skimmed off to collect concentrated ore.

3. Roasting

The concentrated ore is heated in a reverberatory furnace in presence of air. Following changes takes place.

• Volatile impurities and moistures are removed.
• Copper pyrite is decomposed into cuprous sulphide and ferrous sulphide.
  2CuFeS₂ → Cu₂S + 2FeS + SO₂
• Cuprous sulphide and ferrous sulphide are oxidized.
  2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
  2FeS + 3O₂ → 2FeO + 2SO₂

4. Smelting

Roasted ore is mixed with sand and coke and heated in a blast furnace about 15-20 feet in height and 6 feet in diameter. It is made of steel sheet lined with fire bricks. A blast of air enters from the lower part.

Following changes takes place:

1. Unreacted FeS gets oxidized to FeO.
   2FeS + 3O₂ → 2FeO + 2SO₂

2. Cu2O formed by oxidation of Cu₂S reacts with FeS to form Cu₂S.
   2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂
   Cu₂O + FeS → Cu₂S + FeO

3. FeO is converted into slag by the action of sand.
   FeO + SiO₂(flux) → FeSiO₃(slag)

Slag being light and molten is removed from the upper layer. At the hearth of the furnace, molten mass is obtained containing about 50% of copper known as copper matte. It consists of a mixture of sulphide of copper and iron.

5. Bessemerization

Metallic copper is recovered from copper matte by bessemerization process carried in Bessemer converter. The blast of hot air is passed through tuyers. Air is blown through molten matte.

Following changes takes place during bessemerization:

1. Ferrous sulphide left is oxidized to ferrous oxide, which reacts with silica to give slag.
   2FeS + 3O₂ → 2FeO + 2SO₂
   FeO + SiO₂ → FeSiO₃
   Slag is removed from top of molten mass. SO₂ escapes out as waste gas.

2. Cu₂S gets oxidized to Cu₂O. Cu₂O formed reacts with remaining Cu₂S to give free copper metal.
   2Cu₂S + 3O₂ 2Cu₂O + 2SO₂
   Cu₂S + 2Cu₂O 6Cu + SO₂
   Copper metal thus obtained is allowed to cool, dissolved SO₂ escapes out forming large blisters on the surface of metal known as blister copper which contains 98% pure copper.

6. Purification or refining

Blister copper is purified mainly by two methods.

1. Poling: Blister copper is stirred with pole of green wood. The hydrocarbon present in the green wood reduces Cu₂O into metallic copper.
   Cu₂O + C(from green wood) → 2Cu +CO
   Copper obtained after poling is called tough cake copper which is 99% pure.

2. Electro refining: Copper thus obtained may still contains impurities like Ag, Au, Ni, Zn, etc. which can be purified further by electrolysis. The impure copper is taken as anode and thin sheet of pure copper is taken as cathode in a large tank. Acidified CuSO₄ solution is taken as an electrolyte. On electrolysis, anode dissolves and deposited as pure copper in cathode. The impurities are left behind near anode as anode mud.

CuSO_{4}(aq) \rightleftharpoons Cu^{++} + SO_{4}^{--}\\ At\ anode:\ \underset{Impure}{Cu(s)}\rightarrow Cu^{++} + 2e^{-}\\ At\ cathode:\ Cu^{++} + 2e^{-} \rightarrow \underset{Pure}{Cu}

This copper is 99.5% pure.

Physical properties

1. It has characteristics red colour.
2. It is good conductor of heat and electricity.
3. It is highly malleable and ductile.
4. It melts at 1083°C and boils at 2567°C.

Chemical properties

1. Action of air: Copper on exposure to air in presence of carbon dioxide is slowly converted into green basic carbonate.

2Cu + CO_{2} + H_{2}O + O_{2} \rightarrow \underset{\substack{Basic\ copper\\ carbonate(Green)}}{CuCO_{3}.Cu(OH)_{2}}

When copper is heated with air below 1100°C, black oxide of copper is formed.

2Cu+O_{2}\xrightarrow[]{below\ 1100\degree C}\underset{\substack{Cupric\ oxide\\(black)}}{2CuO}

When copper is heated with air above 1100°C, red oxide of copper is formed.

2Cu+O_{2}\xrightarrow[]{above\ 1100\degree C}\underset{\substack{Cuprous\ oxide\\(red)}}{2Cu_{2}O}

2. Action with acids: Copper lies below hydrogen in the electrochemical series and does not displace hydrogen from dilute acids.

1. Action with H₂SO₄: It reacts with dilute H₂SO₄ in presence of air.
   2Cu + 2H₂SO₄ + O₂ → 2CuSO₄ + 2H₂O
   
   But hot and conc. H₂SO₄ gives SO₂.
   Cu + 2H₂SO₄(conc.) → CuSO₄ + SO₂ + 2H₂O

2. Action with HCl: It reacts with dil.HCl in presence of air to give CuCl₂.
   2Cu + 2HCl + O₂ → 2CuCl₂ + H₂O
   
   When HCl gas is passed over heated copper, Cu₂Cl₂ is formed.

\underset{heated}{2Cu}+\underset{gas}{2HCl}\ \rightarrow\ Cu_{2}Cl_{2} + H_{2}

3. Action with HNO₃: Copper dissolve in different concentration of nitric acid.
   Cu + 4HNO₃(conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O
   3Cu + 8HNO₃(dil.) → 3Cu(NO₃)₂ + 2NO + 4H₂O

3. Action with aqueous ammonia
When copper is reacted with aqueous ammonia in presence of oxygen, a complex compound is formed.
2Cu + 8NH₃ + 2H₂O + O₂ → [Cu(NH₃)₄](OH)₂

4. Action with metal ion (Displacement reaction): Copper displaces less electropositive metals like Ag from their water-soluble salt.
Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag

Uses of copper

• It is used for making utensils, containers, electrical wires, kettle, coins, etc.
• It is used in electroplating and electrotyping.
• It forms a number of alloys.
  Brass(Cu+Zn), Bronze(Cu+Sn), German silver(Cu+Zn+Ni), etc.

Compounds of copper

1. Blue Vitriol (CuSO₄.5H₂O)

Preparation:

i. From CuO, CuCO₃ or Cu(OH)₂ with dil. H₂SO₄

\begin{align*} CuO + H_{2}SO_{4} &\rightarrow CuSO_{4} + H_{2}\\ CuCO_{3} + H_{2}SO_{4} &\rightarrow CuSO_{4} + H_{2}O + CO_{2}\\ Cu(OH)_{2} + H_{2}SO_{4} &\rightarrow CuSO_{4} + 2H_{2}O\\ CuSO_{4}(aq) &\xrightarrow[]{crystallization}CuSO_{4}.5H_{2}O \end{align*}

ii. From Cu with conc. H₂SO₄
Cu + 2H₂SO₄ → CuSO₄ + 2H₂O + SO₂

Physical properties

• It is a blue crystalline solid.
• It is soluble in water.

Chemical properties

1. Action of heat

2. Action with NaOH

CuSO_{4} + 2NaOH \rightarrow Cu(OH)_{2} + Na_{2}SO_{4}

3. Action with ammonia solution

CuSO_{4} + 4NH_{4}OH \rightarrow \underset{\substack{Tetramine\ copper\ sulphate\\ Deep\ blue\ colour} }{[Cu(NH_{3})_{4}]SO_{4} + 4H_{2}O}

4. Action with KI

\begin{align*} CuSO_{4} + 2KI &\rightarrow K_{2}SO_{4} + CuI_{2}\\ 2CuI_{2} &\rightarrow Cu_{2}I_{2} + I_{2} \end{align*}

5. Displacement reaction

\begin{align*} Zn + CuSO_{4} &\rightarrow ZnSO_{4} + Cu\\ Fe + CuSO_{4} &\rightarrow FeSO_{4} + Cu \end{align*}

Uses

1. Used as fungicide and germicide.
2. Used in electrolysis.
3. Used in preservative of wood, gum, etc.

2. Black oxide of copper (CuO : cupric oxide)

Uses

1. Used for colouring glass in black or blue colour.
2. Used to estimate carbon and hydrogen in organic compounds.
3. It is used to remove sulphur from petrol.
4. It is used as an oxidizing agent.

3. Red oxide of copper (Cu₂O : cuprous oxide)

Uses

1. Used for preparation of ruby red glass.
2. Used to prepare antirust paint.
3. It is used as pesticides.