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Extraction of Metals

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Minuri Tennakoon

on 9 April 2013

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Transcript of Extraction of Metals

Reducing Agents Coke (an impure form of carbon) A cheap reducing agent. But high temperatures are required making it uneconomical.

Hydrogen used to extract Tungsten

Na and Mg and other metals high up in the reactivity series are reduced by electrolysis.

A more reactive metal can also be used as a reducing agent. Converting Sulfides Ores to Oxides Sulfide ores are converted into oxides by heating them in air, by a process called Roasting. Principles of
metal extraction Extraction of Iron - Reduction by
Carbon in the Blast Furnace Extracting Aluminium - Reduction by Electrolysis. Extraction of Titanium - Reduction
by a more reactive metal Titanium can not be reduced by carbon, because the titanium carbide produced make the metal brittle. Hence Na or Mg is used to extract it from its ore. Extraction of Metals Metals are found in Ores.
(a substance that contains enough metal, for it to be economically worth extracting.)
They are often combined with oxygen or sulfur.
(As well as the metal compound the ore also contains, impurities such as clay and rock called Gangue.)

A reduction reaction has to take place to obtain the metal.

e.g - Fe2O3 Fe
+3 -2 0 e.g - ZnS (s) + 1/2 O2 (g) ZnO (s) + SO2 (g) The SO2 produced is a contributor to acid rain. Hence it is collected and converted into Sulfuric acid.

e.g - SO2 (g) + H2O (l) + 1/2 O2 (g) H2SO4 (l)

The Sulfuric acid produced has a variety of purposes, making the industrial process more economical. At the base of the blast furnace the
blast of hot air burns the coke.

C (s) + O2 (G) CO2 (g)

The reaction is an exothermic process and the temperature is around 2000K, then the CO2 formed reacts with more carbon,

CO2 (g) + C (s) 2CO (g)

The carbon monoxide acts as a reducing agent and reacts with the iron oxide to produce molten iron.

Fe2O3 (s) + 3CO (g) 2Fe (l) + 3CO2 (g) Aluminium is extracted from purified bauxite ore, and largely consists of aluminium oxide.

The extraction process is called the Hall-Heroult.

The oxide is dissolved in molten cryolite (Na3AlF6) which melts at 1240K compared to 2345K 3O 2- 1 1/2 O2 + 6e- Aluminium is produced at the cathode. 2Al 3+ +6e- 2Al Oxygen is
collected at the
anode The overall process is the decomposition on Aluminium Oxide
Al2O3 2Al + 1 1/2 O2 Conversion of Titanium Oxide to Titanium Chloride at 1173K
TiO2 (s) + 2C (s) + 2Cl2 (g) TiCl4 (l) + 2CO (g)
The titanium chloride produced is purified by distillation Reduction of Titanium Chloride with molten Na under an inert argon atmosphere at 1300K
TiCl4 (l) + 4Na (l) Ti(l) + 4NaCl (l) This process is a batch process and is less efficient as the heating vessels have to be re-heated. Tungsten -
Reaction with Hydrogen WO3 + 3H2 W + 3H2O Tungsten ore cannot be reduced by carbon, as it forms a carbide.
It is extracted by reduction with H2 at high temperatures. Environmental Aspects of Metal Extraction Iron Scrap iron can be recycled by being melted down and reformed into other items. This helps to reduce the amount of scrap iron that industries discard in landfill sites.
It can be easily separated from other materials because it is magnetic and has already been extracted from its ore.
However green house gases such as CO2 is released during the extraction and melting process. Aluminium Al can also be recycled by melting (e.g. recycling drinks cans)
Recycling avoids large amounts of CO2 being produced
Recycled Al only uses 5% of the energy used to extract Al from its ore.
Unfortunately there are high transportation and sorting costs of recycling Al.
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