Question

Gold ore is concentrated by leaching with ________.

• A. sodium cyanide in presence of air.
• B. sodium cyanide in absence of air.
• C. sodium hydroxide in presence of air.
• D. sodium hydroxide in absence of air.

Answer 1

The correct option is A sodium cyanide in presence of air.

Gold ore is concentrated by leaching with sodium cyanide in the presence of air.

$4Au\left(s\right)+8C{N}^{-}\left(aq\right)+2H_{2}O\left(l\right)+O_2\left(g\right)\to 4\left[Au\right(CN{)}_2{]}^{-}\left(aq\right)+4O{H}^{-}\left(aq\right)$

Gold is recovered from the solution by the addition of zinc.

$2\left[Au\right(CN{)}_2{]}^{-}\left(aq\right)+Zn\left(s\right)\to \left[Zn\right(CN{)}_4{]}^{2+}\left(aq\right)+2Au\left(s\right)$
Option A is correct.