Gold is then extracted from this complex by displacement technique by using a more electropositive zinc metal.
In this method, zinc (Zn) acts as a reducing agent and it reducesAu+ to Au and itself gets oxidized from Zn to Zn+2 ions which combine with CN− ions and form soluble complex, sodium tetracyanozincate (II).
2[Au(CN)2]−(aq)+Zn(s)→2Au(s)+[Zn(CN)4]2−(aq)