Operation in which size reduction of large lumps to small pieces followed by finely ground material is done by the use of crushers and grinders.

`text(Handpicking:)` To pick up selective pieces of ores.

Operation in which the removal of impurities (gangue) from ore by the following methods :

`text(Levigation or Gravity Separation)` :

(i) This method is based on the difference in densities of the ore gangue particles.

(ii) The powdered ore with gangue particles is introduced in the running stream of water.

(iii) Lighter impurity particles washed off with water and heavier ore particles settle down at the bottom. E.g. Generally oxides & carbonate ores are concentrated by this method.

`text(Magnetic separation)` : Ore and gangue are separated, if only one of them is having magnetic property. Eg. In metallurgy of `Fe`.

Ore `->` magnetic.

impurity `->` non magnetic

In metallurgyof `Sn` (tin stone)

Ore `->` non magnetic (`SnO_2`)

impurity `->` `undersettext(magnetic)[text(wolfmarite) (FeWO_4)]`

(i) It is employed for sulphide ores.

(ii) It is based on the different wetting characteristics of the ore and gangue particles with water and oil.

(iii) Usually ore particles are making as aerofillic & gangue particles as aerophobic by using different reagents.

(iv) Ore particles raised to the surface along with air bubbles and collected at the surface where as gangue particles are wetted and settled down at the bottom of the tank.

(v) Reagents used a froathing agents (pine oil), collectors (sodium ethyl xanthate and potassium ethyl xanthate), Activators (copper sulphate) and depressors (sodium cyanide, alkali).

`text(Collectors)` : These compounds adsorb themselves on polar groups to grains of ores and thus derive them on the surface to pass on into the forth e.g. sodium ethyl xanthate and potassium ethyl xanthate.

`text(Activators and Depressants)` : These compounds activate or depress the floating property of one of the components of the ore and thus help in the separation of different minerals present in the same ore. Copper sulphate is an example of activator, while sodium and potassium cyanides are the examples of depressants e.g. Galena (`PbS`) is usually associated with sphalerite (`ZnS`) and pyrites (`FeS_2`). Floatation is carried out in presence of potassium ethyl xanthate (collector) and sodium cyanide and alkali (depressants). The later compounds depress the flotation property of `ZnS` and `FeS_2` particles and hence only `PbS` particles go into the forth when air is blown in. After the removal of galena, the process is repeated by adding copper sulphate (activator) which activates the floating character of `ZnS` particles and thus this time `ZnS` comes with the froath. The acidification of remaining slurry leads to the flotation of `FeS_2`.

(i) Chemical method of concentration.

(ii) Selective dissolution of ore in strong reagents where as gangue particles are undissolved and gets separated. (Hydrometallurgy)

(iii) Employed for concentrating ores of aluminium, silver, gold etc.

`text(Conversion of the concentrated ore into its Oxide Form)` :

`(a)` `text(Calcination)` :

(i) Ore is heated in absence of air to remove water or `CO_2` from hydrated oxides or carbonates respectively.

(ii) Process temperature is below the melting points of treated ores.

(iii) During calcination moisture, volatile impurities are removed thereby ore becomes porous.

Ex. : `Al_2O_3*2H_2O -> Al_2O_3 + 2H_2O`

`2Fe_2O_3*3H_2O -> 2Fe_2O_3 + 3H_2O`

`CaCO_3 -> CaO + CO_2`

`MgCO_3 -> MgO + CO_2`

`(b)` `text(Roasting)` :

(i) Ore is heated strongly with other substances, usually with oxygen.

(ii) Employed for sulphide ores.

(iii) Process temperature is below the melting points of treated ore.

(iv) Chemical conversion of ore is takes place.

(v) Some of the impurities removed as volatile substances.

`S + O_2 -> SO_2 uparrow`
`4 As + 3O_2 -> 2As_2O_3 uparrow`
`P_4 + SO_2 -> 2P_2O_5 uparrow`

`text(Example)` : (A) Conversion of metal sulphides into oxides.

`2 ZnS + 3O_2 -> 2 ZnO + 2SO_2`

`2 PbS + 3O_2 -> 2 PbO + 2SO_2`

(B) Metal sulphides are converted into sulphates.

`PbS + 2O_2 -> PbSO_4`

`ZnS + 2O_2 -> ZnSO_4`

`text(Smelting)` : (i) Flux is added during smelting, which reduces the melting point of impurities to form as easily fusible substance called as `text(slag)` and can be separated easily because of its lower density.

(ii) Selection of flux depends upon nature of impurity present. Its impurity is acidic or basic flux is employed and vice versa.

(iii) Smelting is usually carried out in blast furnaces or reverberatoty furnace.