5.7 Extraction and Purification of Group 2 Elements | Group 2 Elements | Chemistry 12

Group 2 elements, also known as alkaline earth metals, include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). These elements possess two electrons in their outermost shell. The extraction and purification processes for these elements and their compounds are tailored to their specific chemical and physical properties.

Extraction Process

The extraction of Group 2 elements involves several initial steps to convert naturally occurring ore into a form suitable for reduction to elemental metal.

Ore Preparation

Group 2 elements occur in various minerals, most commonly as carbonates, sulfates, oxides, and silicates.

Mining: The ore containing the desired metal is extracted from the earth.
Crushing: The mined ore is crushed into a fine powder. This increases the surface area, making subsequent chemical reactions more efficient.

Roasting

Many Group 2 carbonates are thermally unstable and decompose upon heating. This process, known as roasting, converts the carbonate into a more reactive metal oxide. For details on thermal decomposition, refer to .

To extract magnesium from magnesium carbonate ( $MgC O_{3}$ ), it is roasted to form magnesium oxide ( $MgO$ ) and carbon dioxide ( $C O_{2}$ ):

$MgC O_{3 (s)} Heat Mg O_{(s)} + C O_{2 (g)}$

Reduction

After ore preparation and roasting, the metal oxide or halide is reduced to obtain the elemental metal. The method depends on the specific element and its reactivity. For comparison of reactivity with Group 1 elements, see .

Electrolysis of Molten Oxides/Halides: For reactive metals like magnesium, electrolysis of its molten oxide or halide (e.g., $MgC l_{2}$ ) is a common reduction method. This process is often carried out in electrolytic cells. For more on cell types, see Types Of Electro-Chemical Cells→.
Chemical Reduction: For elements like calcium and strontium, their halides can be reduced using more reactive metals such as sodium or magnesium. This involves Oxidation Reduction Concepts→.

Purification Process

After initial extraction, the obtained metal often contains impurities. Further purification steps are essential to achieve high-purity metal.

Electrolysis: Pure samples of most alkaline earth metals can be obtained by the electrolysis of their molten chlorides or oxides. In some cases, electrolysis is used as a final purification step for metals already extracted via other means.
Historically, beryllium was first obtained by the reduction of its chloride.
Radium chloride, being radioactive, requires specialized handling and a series of reactions and separations for its extraction and purification.

Examples of Extraction and Purification Methods

Beryllium (Be)

Extraction: Beryllium is typically extracted from beryl ore ( $B e_{3} A l_{2} (Si O_{3})_{6}$ ). This involves acid digestion and solvent extraction to separate beryllium compounds from other components of the ore.
Purification: Beryllium hydroxide, an intermediate compound, is converted into beryllium fluoride ( $Be F_{2}$ ). High-purity beryllium metal is then obtained by reducing beryllium fluoride with magnesium:

$Be F_{2 (s)} + M g_{(s)} Heat B e_{(s)} + Mg F_{2 (s)}$

Magnesium (Mg)

Extraction: Magnesium is most commonly produced by the electrolysis of molten magnesium chloride ( $MgC l_{2}$ ). This $MgC l_{2}$ is often sourced from seawater or brines through the Dow Process.

$MgC l_{2 (l)} Electrolysis M g_{(l)} + C l_{2 (g)}$

Purification: The magnesium metal obtained from electrolysis can be further purified using fractional distillation or vacuum distillation, which separate magnesium from impurities based on differences in their boiling points.

Extraction Process

The extraction of Group 2 elements involves several initial steps to convert naturally occurring ore into a form suitable for reduction to elemental metal.

Group 2 elements occur in various minerals, most commonly as carbonates, sulfates, oxides, and silicates.

Mining: The ore containing the desired metal is extracted from the earth.

Crushing: The mined ore is crushed into a fine powder. This increases the surface area, making subsequent chemical reactions more efficient.

To extract magnesium from magnesium carbonate (

MgC O_{3}

), it is roasted to form magnesium oxide (

MgO

) and carbon dioxide (

C O_{2}

MgC O_{3 (s)} Heat Mg O_{(s)} + C O_{2 (g)}

Electrolysis of Molten Oxides/Halides: For reactive metals like magnesium, electrolysis of its molten oxide or halide (e.g.,

MgC l_{2}

) is a common reduction method. This process is often carried out in electrolytic cells. For more on cell types, see Types Of Electro-Chemical Cells→.

Chemical Reduction: For elements like calcium and strontium, their halides can be reduced using more reactive metals such as sodium or magnesium. This involves Oxidation Reduction Concepts→.

Purification Process

After initial extraction, the obtained metal often contains impurities. Further purification steps are essential to achieve high-purity metal.

Electrolysis: Pure samples of most alkaline earth metals can be obtained by the electrolysis of their molten chlorides or oxides. In some cases, electrolysis is used as a final purification step for metals already extracted via other means.

Historically, beryllium was first obtained by the reduction of its chloride.

Radium chloride, being radioactive, requires specialized handling and a series of reactions and separations for its extraction and purification.

Examples of Extraction and Purification Methods

Extraction: Beryllium is typically extracted from beryl ore (

B e_{3} A l_{2} (Si O_{3})_{6}

). This involves acid digestion and solvent extraction to separate beryllium compounds from other components of the ore.

Purification: Beryllium hydroxide, an intermediate compound, is converted into beryllium fluoride (

Be F_{2}

). High-purity beryllium metal is then obtained by reducing beryllium fluoride with magnesium:

Be F_{2 (s)} + M g_{(s)} Heat B e_{(s)} + Mg F_{2 (s)}

Extraction: Magnesium is most commonly produced by the electrolysis of molten magnesium chloride (

MgC l_{2}

). This

MgC l_{2}

is often sourced from seawater or brines through the Dow Process.

MgC l_{2 (l)} Electrolysis M g_{(l)} + C l_{2 (g)}

Purification: The magnesium metal obtained from electrolysis can be further purified using fractional distillation or vacuum distillation, which separate magnesium from impurities based on differences in their boiling points.