Question

Sulphide ores of metals are usually concentrated by froth floatation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?

• A. Argentite
• B. Galena
• C. Copper pyrite
• D. Sphalerite

Answer 1

Answer: (A)

Argentite

Answer 2

Froth Floatation Process: This process is best suitable for sulphide ores. The process is based on different wetting characteristics of the ore and gangue particles with water and pine oil. The ore is wetted by oil and impurities are wetted by water. Ore particles are adsorbed on potassium or sodium ethyl xanthate (as a collector) and come at the surface along with the froth. Froth stabilizer (cresols, aniline) stabilize the froth.
But Argentite is not concentrated by this method. The following method is used to concentrate Argentite:

$$Ag _{2} S +4 NaCN \rightarrow 2 Na \left[ Ag ( CN )_{2}\right]+ Na _{2} S$$

Silver is obtained by reaction with $Zn$ :

$$2 Na \left[ Ag ( CN )_{2}\right]+ Zn \rightarrow Na _{2}\left[ Zn ( CN )_{4}\right]+2 Ag$$