Question

Metal extracted from seawater is:
A.Be
B.Mg
C.Ba
D.Ca

Answer 1

Hint:Look at the composition of seawater. Identify the mineral which is present in a larger concentration. Check whether it is feasible to be extracted from seawater. Find out the metals extracted using the Dow’s seawater process mainly group 2 elements.
Complete step by step answer:
Seawater contains a rich source of many commercially important minerals. It is an abundant source of metal ions like $C{l^ - }$,$N{a^ + }$,$M{g^{2 + }}$, $S{O_4}^{2 - }$, $C{a^{2 + }}$ and ${K^ + }$.

The amount of these salts in a volume of seawater varies because of the addition or removal of water locally (e.g., through precipitation and evaporation).

Mg can be extracted from seawater by Dow’s seawater process.

About 0.13% of $M{g^{2 + }}$is present in seawater as $MgC{l_2}$ and the extraction of magnesium depends on the fact that $Mg{\left( {OH} \right)_2}$ is very much less soluble than $Ca{\left( {OH} \right)_2}$.

Slaked lime ($Ca{\left( {OH} \right)_2}$) is added to seawater, and the calcium ions dissolve and $Mg{\left( {OH} \right)_2}$ is precipitated. This is filtered off, treated with HCl to produce magnesium chloride and electrolyzed.

The electrolysis may be carried out on fused $MgC{l_2}$ or on partially hydrated $MgC{l_2}$.
$Ca{\left( {OH} \right)_2} + MgC{l_2} \to Mg{\left( {OH} \right)_2} + CaC{l_2}$
$Mg{\left( {OH} \right)_2} + HCl\xrightarrow{{heat}}MgC{l_2}$ (for electrolysis)
The metals of group 2 in the periodic table are themselves strong reducing agents. They are strongly electropositive and react with water, and so aqueous solutions cannot be used for displacing them with another metal or for electrolytic production.

These metals can be obtained by electrolysis of the fused chloride, with sodium chloride added to lower the melting point.

The concentrations of Be, Ba, and Ca are less in seawater. Hence the extraction of these metals from seawater is not economically feasible.
The correct answer is (B) Mg.

Note: Calcium and potassium compounds are produced as by-products in salt- or magnesium-extraction processes or by processing seaweeds, which extract these elements from seawater and concentrate them in their cells; however, these elements are not commercially extracted directly from seawater itself in any significant amount.