Extraction of Aluminum, Copper, Zinc & Iron Video

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  • 0:04 General Methods of Extraction
  • 0:46 Extraction of Aluminum
  • 2:49 Extraction of Copper
  • 5:00 Extraction of Zinc & Iron
  • 7:32 Lesson Summary
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Lesson Transcript
Instructor: Saranya Chatterjee

Saranya has a masters degree in Chemistry and in Secondary Education. She has taught high school, AP chemistry for 2 years and is teaching undergraduate college chemistry for 3 years.

This lesson will talk about extraction of some metals like aluminum, copper, zinc and iron. It will discuss some processes like electrolysis, carbon reduction and self reduction.

General Methods of Extraction

In this lesson, we're going to discuss the extraction of four metals: aluminum, copper, iron and zinc. In the periodic table, Aluminum is a metal of Group 13 and copper, iron and zinc are transition metals. In general, metals are extracted from their ore, which is a naturally occurring substance. Aluminum is extracted electrolytically, which involves passing electricity through an ionic substance in a solvent with the presence of two rods called electrodes. During the process, the metal gets deposited in one of the electrodes. Copper is extracted by the self-reduction method. Iron and zinc are both extracted by carbon reduction method from their respective ores.

Extraction of Aluminum

Aluminum is extracted electrolytically from bauxite, which is aluminum ore. Bauxite contains hydrated alumina (Al2 O3) with some proportions of iron oxide. The extraction process involves the following steps.

A. Purification of bauxite - This is a two-step process called Bayer's process:

  1. First, we dissolve bauxite in aqueous sodium hydroxide (NaOH) by digestion. Bauxite with higher hydroxide contents (Al(OH)3) are treated at 120-140° C with dilute (3M) NaOH and bauxite with higher oxide content (AlOOH) is treated at a higher temperature (200-250° C) and a higher pressure (35 atm) with 5-7M NaOH.
  2. Next, the insoluble impurities are separated by filtration. Al(OH)3 is precipitated by carbon dioxide and ignited to ~1200° C to obtain Al2 O3.

B. Purified bauxite is then dissolved in cryolite, which is 5-7% CaF2 , 5-7% AlF3, 2-8% Al2 O3 and electrolyzed at 950° C in a carbon-lined steel cathode with hard carbon rods as the anode. Li2 CO3 is used to (i) lower the melting point of the electrolyte, (ii) permit a larger current flow, and (iii) reduce fluorine emission.

The resulting reactions are produced:

Al2 O3 → 2Al3+ + 3O--

At cathode: 2 Al3++ 6e- → 2Al

At anode: 3O-- - 6e- → 3O

Aluminium Extraction process
extraction of aluminium

Extraction of Copper

Chalcopyrite (CuFeS2) is the commonest copper ore. Copper is mainly extracted from the sulphide ore (Cu2 S) by the self-reduction process. The ores are often low grade (0.5% Cu) and require concentration (up to 15-20% Cu). The process contains the following steps.

  1. Concentration of the ore by froth floatation method, where hydrophobic materials are separated from hydrophilic substances.
  2. Roasting and smelting - The sulphide ore is mixed with silica (SiO2) at ~1400° C in a reverberatory furnace where impurities like FeS are preferentially oxidized prior to Cu2 S.
    2FeS + 3O2 → 2FeO + 2SO2
    The FeO forms slag (stony waste matter separated from metals during the smelting) with silica. The molten mass separates as the top layer of slag (FeSiO3) and the lower layer is of copper matte mainly composed of Cu2 S and FeS.
  3. Self-reduction - The molten matte is further oxidized in air when the remaining FeS is mainly oxidized. More silica is added, which forms more slag with the iron oxide. After removing the slag, the copper sulphide is partly oxidized by air to Cu2 O, and this Cu2 O then combines with the remaining Cu2 S, producing copper.
    2Cu2 S + 3O2 → 2Cu2 O + 2SO2
    2Cu2 O + Cu2 S → 6Cu + SO2
    As the sulphur dioxide leaves the metal during cooling, the crude copper develops blisters and is known as 'blister copper'.
  4. The crude copper is refined electrolytically using acidified copper sulphate solution as the electrolyte and crude copper as anode and pure copper as cathode.

Copper Extraction process
extraction of copper

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