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# What is the process of leaching?

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## Leaching“Leaching is often used if the ore is soluble in some suitable solvent.” eg, acids, bases, and suitable chemical reagents.Procedure for leachingIn silver and gold metallurgy, the metal is leached with a dilute solution of Sodium cyanide $\left(\mathrm{NaCN}\right)$ or Potassium cyanide $\left(\mathrm{KCN}\right)$ in the presence of oxygen. Later, a replacement reaction is used to obtain the metal.The reaction is as follows:-$4\mathrm{M}\left(\mathrm{s}\right)+8{\mathrm{CN}}^{–}\left(\mathrm{aq}\right)+2{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{aq}\right)+{\mathrm{O}}_{2}\left(\mathrm{g}\right)\to 4{\left[\mathrm{M}{\left(\mathrm{CN}\right)}_{2}\right]}^{-}\left(\mathrm{aq}\right)+4{\mathrm{OH}}^{–}\left(\mathrm{aq}\right)$In the above reaction $\mathrm{M}$ is $\mathrm{Ag}$ or $\mathrm{Au}$.$2{\left[\mathrm{M}{\left(\mathrm{CN}\right)}_{2}\right]}^{-}\mathrm{aq}+\mathrm{Zn}\left(\mathrm{s}\right)\to {\left[\mathrm{Zn}{\left(\mathrm{CN}\right)}_{4}\right]}^{2-}\left(\mathrm{aq}\right)+2\mathrm{M}\left(\mathrm{s}\right)$ExampleThe sliver is obtained by the leaching process is as follows:-$4\mathrm{Ag}\left(\mathrm{s}\right)+8{\mathrm{CN}}^{–}\left(\mathrm{aq}\right)+2{\mathrm{H}}_{2}\mathrm{O}\left(\mathrm{aq}\right)+{\mathrm{O}}_{2}\left(\mathrm{g}\right)\to 4{\left[\mathrm{Ag}{\left(\mathrm{CN}\right)}_{2}\right]}^{-}\left(\mathrm{aq}\right)+4{\mathrm{OH}}^{–}\left(\mathrm{aq}\right)$$2{\left[\mathrm{Ag}{\left(\mathrm{CN}\right)}_{2}\right]}^{-}\mathrm{aq}+\mathrm{Zn}\left(\mathrm{s}\right)\to {\left[\mathrm{Zn}{\left(\mathrm{CN}\right)}_{4}\right]}^{2-}\left(\mathrm{aq}\right)+2\mathrm{Ag}\left(\mathrm{s}\right)\phantom{\rule{0ex}{0ex}}\mathrm{Silver}\mathrm{cyanide}\mathrm{Zinc}\mathrm{cyanide}$

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