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Question
Extraction of gold and silver involves leaching the metal with CN– ion. The metal is recovered by ______.
Options
displacement of metal by some other metal from the complex ion.
roasting of metal complex.
calcination followed by roasting.
thermal decomposition of metal complex.
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Solution
Extraction of gold and silver involves leaching the metal with CN– ion. The metal is recovered by displacement of metal by some other metal from the complex ion.
Explanation:
The metal in cyanide process is recovered by displacement of metal by some more reactive metal from the complex.
The metal is later recovered by displacement method.
\[\ce{4M + 8CN^{-} + 2H2O + O2 -> 4[M(CN)2]^{-} + 4OH^{-}}\]
\[\ce{2[M(CN)2]^{-} + Zn -> [Zn(CN)4]^{2-} + 2M}\]
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