Test: Metallurgy Process of Concentration of Ores (Old NCERT) - NEET MCQ

The ores even after concentration , contain some ganghue.To remove these gangue particle cortain substance are mixed to form a fushible ore which combite with the gangue to form a fusible meterial which is not solution in molten metal . The sulstances used are called fluxed and the fasible merterial formed during reduction process is called slag
Slag is usually lighly and thus on the surface of the moltes metal

Flaxtes are classified as (i) acidic flox and (ii) basic , flex An acoidic flux siles bores etc is the chenical substans which removes the imparities.

This method is based upon the fact that the surface of sulphide over is preferentially wetted by oils while that of gangue is preferentially wetted by water.

In this process the finely divided powdered argentite or the native silver or gold is treated with a dilute solution (0.5%) of sodium or potassium cyanide while a current of air is continuously passed. As a result silver pass into solution forming their respective soluble complex cyanides while the impurities remain unaffected which are filtered off.

The ore is crushed into a fine powder and mixed with water to form suspension.

Electromagnetic separation method of concentration is employed when either the ore or the impurities associated with it are magnetic in nature. Tinstone or cassiterite (SnO₂) an ore of tin being non-magnetic can be separated from magnetic impurities (FeWO₄).

The mineral particle becom es wet by oils while the gangue particles by water. A rotating paddle agitates the mixtures and draws air in it. As a result froth is formed which carrier the mineral particles. The froth is light and is skimmed of. If is then dried for recovery of the ore particles.

Leaching This process consists in treating the powdered ore with a suitable reagent (such as acids, bases or other chemicals) which can selectively dissolves the ore but not the impuritier. It is used to extract silver metals.

The ore particles preferentially wetted by the oil become lighter and thus rise to the surface along with the froth while the gangue particle wetted by wated become heavier and thus settle down at the bottom.

Cinnabar, Galena , zinc blende are concetrated by froth floatation method.

They are light and water repellent.

Hoope's method is used to obtain aluminium of very high purity. The metal obtained in the Hall-Heroult process is about 99% pure and for most purposes it is taken as pure metal. However further purification of aluminium can be carried out by the Hoope’s process. This is an electrolytic process.

The common impurities present in bauxite are Fe₂O₃ and SiO₂.

Flux is not involved in froth floatation process.

The process by which lighter earthly particles are free from the heavier ore particles by washing with water is called levigation.

In the Baeyer process Al₂O₃ is obtained from bauxite ore by treating the powered ore with a strong solution of NaOH when alumina (Al₂O₃) dissolves forming sodium mefa-aluminate leaving behind impurities.

(i) → (r), (ii) → (p), (iii) → (q), (iv) → (s)

(i) → (q), (ii) → (r,t), (iii) → (p), (iv)→ (s)

Galena, zinc blende and copper iron pyrites are concentrated by froth floatation method.

Bauxite, horn silver, native gold, tinstone.

In this reaction oxidation state of silver is zero.

Pitche blende, tinstone, chromite are purified by levigation.

Wolframite, chromite, magnetite, rutile (contain iron impurities).

Because cresol and aniline are froth stabilisers, but only ethyl xanthate, pine oil which enhance non-wettability of ore particles.