A. Write the principle of method used for the refining of germanium.

B. Out of PbS and PbCO₃ (ores of lead), which one is concentrated by froth floatation process preferably?

C. What is the significance of leaching in the extraction of aluminimum?

A. Refining of germanium is done by the zone-refining method. This method is based on the principle that the impurities are more soluble in the melt of metal than in the solid state of the metal.

B. Out of PbS and PbCO₃ , PbS is concentrated by froth floatation process. It is used for removing gangue from sulphide ores. It is commonly used for sulphide ores. This method is based on the principle that ore particles are preferentially wetted by oil and gangue by water. Froth is created here, which carries the mineral particles. The froth floats and is skimmed off. It is dried for recovery of the ore particles.

C. Bauxite is the principal ore of aluminium which contains SiO₂ , iron oxides and TiO₂ as impurities. In leaching of alumina, concentration is carried out by digesting the powdered ore with a concentrated solution of NaOH at 473-523 K and 35-36 bar pressure. Here, alumina is leached out as sodium aluminate leaving back all impurities.