Question

Gold is extracted by hydrometallurgical process, based on its property:
A.Of being electropositive
B.Of being less reactive
C.To form complex which are water soluble
D.None of these

Answer 1

Hint: We know that hydrometallurgy is the technique of isolation of metal from ore by making an aqueous solution of salt of the metal and getting back the metal from the solution. In this process, the metal is obtained from the ore of metal by dissolving the ore of metal in a desired solvent.

Complete step by step answer:
We have to know the process of hydrometallurgy takes place in three stages,
1.Leaching
2.Concentration and purification of solution
3.Recovery of metal (or) compound of metal
Usually, in the process of hydrometallurgy, the ore is concentrated by leaching process (or) metal dissolution (or) metal in water with extra agents. The waste is separated and the leach solution is purified. Then, the precipitation of the metal (or) one of its pure compounds from the leach solution is done by the process of electrolysis (or) by common method. Dilute sulfuric acid, sodium hydroxide are examples of common leaching agents.
According to the principle of hydrometallurgy, a less electropositive metal gets displaced by more electropositive metal from its solution.
In the hydrometallurgy of gold, we have to leach gold from their native ores by dilute solution of potassium cyanide (or) sodium cyanide in the presence of air (oxygen) and complex of cyanides that are water soluble are obtained. We can call this process the Macarthur forest cyanide process.
We can write the equation for the extraction of gold by hydrometallurgy process as,
$4Au + 8NaCN + 2{H_2}O + {O_2} \to 4Na\left[ {Au{{\left( {CN} \right)}_2}} \right] + 4NaOH$
$2Na\left[ {Au{{\left( {CN} \right)}_2}} \right] + Zn \to N{a_2}\left[ {Zn{{\left( {CN} \right)}_4}} \right] + 2Au$
$N{a_2}\left[ {Zn{{\left( {CN} \right)}_4}} \right]$ is a soluble complex.

So, the correct answer is Option C.

Note: We can use hydrometallurgy to produce more than 70 elements that are metals. Silver, copper and zinc are some of the examples of metals that are produced by process of hydrometallurgy. We can also extract pure alumina from bauxite ore by hydrometallurgy process.