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?

Depressant used in the concentration of an ore containing $ZnS$ and $PbS$ is

In the leaching method,bauxite ore is digested with a concentrated solution of $NaOH$ that produces $X$. When $CO_2$ gas is passed through the aqueous solution of $X$,a hydrated compound $Y$ is precipitated. $X$ and $Y$ respectively are

Difference in density is the basis of

The substance used as froth stabilisers in the froth-floatation process is

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