This is because oxides are reduced to metals easily while sulphides are not. So, sulphide ores are converted to oxide before reduction.

Zr and Ti are refined by van Arkel method. It involves 2 steps

(a) Formation of iodide e.g., zirconium

$$\mathrm{Zr}+2 \mathrm{I}_2 \longrightarrow \mathrm{ZrI}_4$$

(b) Decomposition of iodide

$\mathrm{ZrI}_4 \xrightarrow{1800 \mathrm{~K}} \underset{\text { Pure }}{\mathrm{Zr}}+2 \mathrm{I}_2$

During extraction of metals by electrochemical method the following two points must be considered

(i) Reactivity of metals If the metals are quite reactive and are expected to react with water then the metals should be extracted by the electrolysis of their purified molten ore rather than their aqueous solution.

(ii) Suitability of electrodes The electrods selected should not react with the product of electrolysis. If at all they react, then the electrodes must be made up of a material which is quite cheap since their periodic replacement should not increase the cost of the process.

Role of flux in metallurgical process

(i) Flux is used to remove the gangue by combining with it. Thus, slag formation takes place.

(ii) It makes the molten mass more conducting.

Metals of high grade like germanium, silicon etc., used as semiconductors are refined by zone refining method.

Principle This method is based upon the principle that impurities are more soluble in molten state of metal than in solid state.