Question

How is gold extracted from its ore?

Answer 1

Gold is usually found alone or alloyed with mercury. Various methods too.Concentration of ore is performed to remove unwanted material. Various methods are Leaching , amalgamation, Froth Floatation, .Leaching method is most commonly used. Electrolytic refining is used to purify gold.

Complete answer:
-Gold is extracted from its ores such as calaverite, sylvanite and petzite.
-First step is Concentration of ore. It removes unwanted material such as clay, sand also called gangue.
-Froth floatation and leaching are used for concentration of ore.
- Froth Floatation:
-The method is used for removing gangue from sulphide ore.
- In this, suspension of powdered ore is prepared using water, then collectors and stabilizers are added.
-Collectors like oils, fatty acids impart hydrophobicity to mineral particles and froth stabilisers like cresol stabilize froth`
-The mineral particles become wet by oil and gangue by water. Mixture is agitated using a rotating paddle and draws air. Froth is created which carries mineral particles. As the froth is light, it is skimmed off and dried.
- Leaching:
-when ore is soluble in some suitable ore, Leaching is used.
-In this method, gold is leached with a dilute solution of cyanide in the presence of air.
$\begin{aligned} & \text{4Au + 8C}{{\text{N}}^{\text{-}}}\text{+2}{{\text{H}}_{\text{2}}}\text{O+}{{\text{O}}_{\text{2}}}\xrightarrow{{}}\text{4 }\\!\\![\\!\\!\text{ Au(CN}{{\text{)}}_{\text{2}}}{{\text{ }\\!\\!]\\!\\!\text{ }}^{\text{-}}}\text{+4O}{{\text{H}}^{\text{-}}} \\\ & \text{2 }\\!\\![\\!\\!\text{ Au(CN}{{\text{)}}_{\text{2}}}{{\text{ }\\!\\!]\\!\\!\text{ }}^{\text{-}}}\text{+Zn}\xrightarrow{{}}{{\text{ }\\!\\![\\!\\!\text{ Zn(CN}{{\text{)}}_{\text{4}}}\text{ }\\!\\!]\\!\\!\text{ }}^{\text{-2}}}\text{+2Au} \\\ \end{aligned}$
-Gold is replaced with zinc and it is obtained.
-Gold is refined using electrolysis. In this anode is made up of impure gold and strips of gold in pure form act as cathode. Anode and cathode are kept in electrolyte containing soluble salt of gold. Pure gold is obtained at cathode and impurities deposit at anode called as anode mud.

Note:
In amalgamation method, powdered ore is passed over plates containing mercury. Mercury and gold from an amalgam. It is heated till mercury boils off and leaves gold. For extraction of any metal from its ore, the first step is concentration of ore, then crude metal is extracted from concentrated ore and refined.