Question

Sulphide ores of metals usually concentrated by the froth floatation process. Which one of the following sulphide ores offers an example and is concentrated by chemical leaching?
A.Galena
B.Copper pyrite
C.Sphalerite
D.Argentite

Answer 1

Hint: Leaching is a process extensively used in metallurgy where ore is pickled with chemicals to change the valuable metals within into soluble salts though impurity remains insoluble in the solution. It can be washed out and treated to give the pure metal. The material left over is usually discussed as tailings.

Complete answer:
We know that generally sulphide ores of metals are usually concentrated by the froth floatation process.
Coming to the given options, Galena, Copper pyrite, Sphalerite are the sulphide ores concentrated by the froth floatation process.
But Argentite is not concentrated by the froth floatation method.
Purification of gold and silver involves chemical leaching of the ore with cyanide (\[C{{N}^{-}}\]).
Argentite (\[A{{g}_{2}}S\]) is an ore of silver.
Silver is extracted from argentite by using the Mac-Arthur and Forrest cyanide process. In this process argentite (\[A{{g}_{2}}S\]) is treated with sodium cyanide (\[NaCN\]) and converts argentite in to a sodium salt (\[NaAg{{(CN)}_{2}}\]) later the sodium salt of argentite is treated with zinc to convert silver metal in to soluble form.
 \[\begin{align}
  & A{{g}_{2}}S+4NaCN\to 2NaAg{{(CN)}_{2}}+N{{a}_{2}}S \\
 & 2NaAg{{(CN)}_{2}}+Zn\to N{{a}_{2}}Zn{{(CN)}_{4}}+Ag \\
\end{align}\]

So, argentite is the sulphide where silver can be extracted through a chemical leaching process.

Additional information:
Froth Floatation Process: This process is the best appropriate method for sulphide ores. In this process ore is wetted with oil and impurities are wetted with water. Later ore particles are adsorbed by using potassium (as a collector) and ores come to the surface along with the froth.

Note: Silver is a costly element and some of the ore settles in the bottom of the tub during the froth flotation process. Therefore, loss of valuable silver metal occurs through the froth floatation process. So, silver is extracted through leaching.