The complex formed when $Al_2O_3$ is leached from Bauxite using concentrated $NaOH$ solution is,

In the purification of bauxite by Hall's process:

For which ore of the metal,froth floatation method is used for concentration?

In the froth-floatation process,palm oil functions as:

While extracting an element from its ore,the ore is ground and leached with dilute $KCN$ solution to form the soluble product potassium argentocyanide. The element is

Which one of the following is not a method of concentration of metals?