Learning Objective

In this lesson we will learn about different methods for obtaining pure metals from ore, and how the method used depends on the chemical reactivity of the particular metal.

Learning Outcomes

By the end of this lesson you will be able to:

  • Describe how the form in which a metal exists in nature, and the method used to extract it, are both related to the metal’s reactivity.
  • Define a native metal and give examples of methods used to separate them.
  • Describe the processes of carbon reduction and electrolysis for extracting metals from ore.
  • Compare the energy requirements for native metal separation, carbon reduction and electrolysis, and give examples of metals extracted by these methods.

Extraction of Metals

1 | Extracting and Refining Metals from Ore

2 | Refining Native Metals

3 | Carbon Reduction of Metals

4 | Electrolysis of Metals

5 | Summary

 

 extraction of metals worksheet  year 10 chemistry pdf workbook  Year 10 Chemistry Print Workbook Australian Curriculum

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Extracting and Refining Metals from Ore

  • Metals exist in the earth’s crust either as native metals (elements) or minerals (compounds).
  • The rocks and sand in which metal deposits are found are known as ores.
  • Metal ores are mined from the earth’s crust, then metals are extracted from the ore.
  • The form in which a metal exists in an ore depends on its chemical reactivity.
  • The least reactive metals, such as gold, silver and copper, usually exist as native metals.
  • They only need to undergo physical separation processes to be extracted.
  • More reactive metals, such as iron and aluminium, exist as minerals.
  • They need to undergo chemical separation processes to be extracted.
  • The type of chemical process for extracting metals from minerals depends on how reactive the metal is.
  • Metals with an intermediate reactivity, such as iron and zinc, are obtained by carbon reduction – a type of displacement (redox) reaction carried out at high temperatures.
  • The most reactive metals, such as aluminium and magnesium, are obtained by electrolysis – a process which requires the input of electric current.
  • Once extracted, metals undergo further refining (purification).

 
metal extraction method reactivity

The method for extraction of a metal depends on its reactivity.

 


Refining Native Metals

  • Native metals, such as gold and silver, can be physically extracted from ore.
  • For example, gold and copper can be separated from crushed rock by a process known as froth flotation, which uses detergents to create floating bubbles that adhere to metal particles, while other materials settle out and are removed.

 
metal separation froth flotation

Froth flotation is a method for physically separating native metals from ore.

 
 
metal separation froth flotation copper gold

Froth flotation of copper.

(Image: Andreslan, Wikimedia Commons)

 


Carbon Reduction of Metals

  • Metals with an intermediate reactivity, such as iron and zinc, which form part of minerals, need to be chemically extracted from ore.
  • This is done by a process called carbon reduction.
  • Carbon reduction is a type of displacement (redox) reaction, where carbon is used to displace the metal from the mineral compound.
  • The crushed ore is mixed with carbon and heated to a molten state – a process known as smelting, which takes place in a blast furnace.
  • In the subsequent chemical reaction, the metal-containing compound is reduced (loses oxygen) and the carbon is oxidised (gains oxygen).
  • Example
  • iron oxide  +  carbon  (+ heat)    iron  +  carbon dioxide
  • 2 Fe2O3  +  3 C    4 Fe  +  3 CO2
  • The smelting process also includes limestone, which combines with sand and other waste materials to form slag.
  • The less dense slag floats on top of the molten metal and is removed.

 
metal extraction carbon reduction blast furnace

Carbon reduction is a method for extracting metals with an intermediate reactivity.

 
 
blast furnace iron ore extraction

Iron ore blast furnace.

(Image: zephylwer0, Pixabay)

 


Electrolysis of Metals

  • Very reactive metals, that sit above carbon on the reactivity series, such as aluminium and magnesium, cannot be extracted by carbon reduction.
  • This is because they are more reactive than carbon and therefore cannot be displaced by it.
  • Instead, these reactive metals are extracted by a process called electrolysis.
  • Electrolysis is a non-spontaneous redox reaction, which involves the passing of an electric current through molten ore.
  • As a result of the electric current, electrons are added to the metal ions, thus reducing them to elemental metal.
  • Example
  • aluminium oxide  (+ heat + electricity)    aluminium  +  oxygen
  • 2 Al2O3    4 Al  +  3 O2
  • Since electrolysis is a redox reaction, there are two reactions taking place.
  • The first is the reduction reaction, involving the metal.
  • Example
  • Al3+  +  3 e    Al
  • The second is the oxidation reaction, involving the non-metal.
  • Example
  • 2 O2-    O2  +  4 e
  • Electrolysis involves a positive electrode, known as the anode, and a negative electrode, known as the cathode.
  • The reduction of metals takes place at the cathode.
  • Positive metal ions are attracted to the negative electrode, where they gain electrons (are reduced) to become metal atoms.
  • The oxidation reaction takes place at the anode.
  • Negative non-metal ions are attracted to the positive electrode, where they lose electrons (are oxidised) to become non-metal atoms (which then form molecules).

 
metal extraction electrolysis

Electrolysis is used for extracting very reactive metals from ore.

 
 
aluminium smelter metal extraction electrolysis

Aluminium smelter.

(Image: Yakov Fedorov, Wikimedia Commons)

 


Summary

  • In nature, most metals exist as compounds (minerals) embedded in surrounding rock (ore).
  • Only the least reactive metals, such as gold and silver, exist in their elemental metallic form.
  • These metals are known as native metals.
  • The chemical reactivity of metals also determines their method of extraction.
  • Native metals undergo physical separation processes, such as froth flotation.
  • Froth flotation uses detergents to create floating bubbles that adhere to metal particles, while other materials settle out and are removed separately.
  • Metals with an intermediate reactivity, such as iron and zinc, are chemically extracted from minerals by a process known as carbon reduction.
  • Carbon reduction is a type of redox reaction, where carbon is used to displace a metal from a compound.
  • The crushed ore is mixed with carbon and limestone, then heated to a molten state (smelted) in a blast furnace.
  • In the subsequent chemical reaction, the metal-containing compound is reduced (loses oxygen) to form pure metal, and the carbon is oxidised (gains oxygen) to form carbon dioxide.
  • Very reactive metals are extracted by a process called electrolysis.
  • Electrolysis is a non-spontaneous redox reaction, which involves the passing of an electric current through molten ore.
  • The electric current causes electrons to be added to metal ions, thus reducing them to metal atoms.

 
refined zinc metal bars

(Image: Björn Wylezich, Adobe Stock)

(Header image: shibang, Pixabay)

 

 extraction of metals worksheet  year 10 chemistry pdf workbook  Year 10 Chemistry Print Workbook Australian Curriculum

Click images to preview the worksheet for this lesson and the Year 10 Chemistry Workbook (PDF and print versions)