During the extraction of $Fe$,which reaction is performed in the combustion zone?

What is the role of tuyeres used in a blast furnace for the extraction of iron?

Calcium is extracted by the electrolysis of

Extraction of gold and silver involves leaching with $CN^{-}$ ion. Silver is later recovered by

Cast iron is used for the manufacture of

Low grade $Cu$ ores are available and $Zn$ and $Fe$ scraps are also available. Which scrap among the two would be more suitable for reducing the leached $Cu$ ore (economically)?