Metallurgical operations-Step 1 - Concentration of ores

Question 1

Principle of hydraulic washing/gravity separation

Answer 1

Based on the differences in gravities/weights of the ore and the gangueparticles or seaparation of heavy particles from light using a stream of water

Question 2

Principle of leaching

Answer 2

Separation of gangue when ore is soluble in some suitable solvent while gangue is not.

Question 3

Principle of magnetic separation

Answer 3

Separation of magnetic particles from non- magnetic particles using powerful electromagnets

Question 4

Principle of froth floatation

Answer 4

Separation of gangue where oil wets ore and water wets gangue

Question 5

Role of collectors(eg pine oil) in froth floatation

Answer 5

Preferrentially wets ore

Question 6

Role of stabilizers(cresol) in froth floatation

Answer 6

Stabilizes the froth

Question 7

Role of depressant(NaCN) in froth floatation

Answer 7

Prevents one type of ore from forming froth in a mixture of sulphide ores. For
example, in case of an ore containing ZnS
and PbS, the depressant used is NaCN. It
selectively prevents ZnS from coming to the
froth but allows PbS to come with the froth.

Question 8

Definition of gangue

Answer 8

Ore is usually contaminated with earthly or undesired

materials known as gangue.

Question 9

Definition of benefaction/concentration

Answer 9

Removal of the unwanted materials (e.g., sand, clays, etc.) from the ore
is known as concentration, dressing or benefaction.

Question 10

Role of NaCN in Froth floatation

Answer 10

Depressant

Question 11

Role of NaCN in the metallurgy of gold/silver

Answer 11

Leaching agent- brings the metal into solution by forming a complex

Question 12

Role of Zn in the leaching of gold/silver

Answer 12

Reducing agent/ displaces the metal from solution to give pure metal as it easily forms complexes.

Question 13

Role of CO2 in leaching of alumina

Answer 13

The aluminate in solution is neutralised by passing CO2 gas and hydrated Al2O3 is precipitated.

Question 14

Conditions for leaching of alumina

Answer 14

Concentration is carried out by digesting the powdered ore with a concentrated solution of NaOH at 473 – 523 K and 35 – 36 bar pressure.

Question 15

Role of NaOH in leaching of alumina

Answer 15

Suitable solvent to dissolve alumina

Question 16

Equations for leaching of gold or silver

Answer 16

4M(s) + 8CN–(aq)+ 2H2O(aq) + O2(g) → 4[M(CN)2]– (aq)
+ 4OH–(aq) (M=
Ag or Au)
2[M(CN)2]- (aq) + Zn(s) → [Zn(CN)4]2-(aq) + 2M(s)

Question 17

Equations for leaching of alumina

Answer 17

Al2O3(s) + 2NaOH(aq) + 3H2O(l) → 2NaAl(OH) 4
temp= 473 – 523 K and
pressure= 35 – 36 bar
2NaAl(OH)4 + CO2(g) → Al2O3.xH2O(s) +
2NaHCO3 (aq)
Al2O3.xH2O(s) → Al2O3(s) + xH2O(g) ;temp=1470K

Question 18

Ores concentrated by froth floatation

Answer 18

sulphide ores- galena, copper pyrites, zinc blende

Question 19

How is leaching carried out in case of low grade copper ores?

Answer 19

Copper is extracted by hydrometallurgy from low grade ores. It is leached out using acid or bacteria.

Question 20

Name the process used for leachng alumina

Answer 20

Bayer’s process