Tag: general principles of metallurgy

Questions Related to general principles of metallurgy

The significance of leaching in the extraction of aluminium is:

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. it helps to remove the impurities like $SiO _2, Fe _2O _3,$ etc from the bauxite ore

  2. it converts the ore into oxide

  3. it reduces melting point of the ore

  4. it eliminates water from bauxite.

Show answer
Correct Option: A
Explanation:
  • Bauxite is the principal ore of aluminium.  The impurities present in bauxite are $SiO _2$, iron oxides and titanium oxide ($TiO _2$). 
  •  $Al _2O _3$ is extracted out as sodium aluminate. The impurity, $SiO _2$ too dissolves forming sodium silicate. Other impurities are left behind.
$Al _2O _3+2NaOH+3H _2O \rightarrow 2Na[Al(OH) _4]$
  • Thus, leaching is used to remove the impurities present and hence option $A$ is the correct option.

Sulphide ore of zinc/copper is concentrated by:

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. forth floatation

  2. electromagnetic process

  3. gravity process

  4. distillation

Show answer
Correct Option: A
Explanation:
  • Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water.
  • Collectors and froth stabilizers are added to it. Collectors (e.g., pine oils, fatty acids, xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilizers (e.g., cresols, aniline) stabilize the froth.
  • The mineral particles become wet by oils while the gangue particles by
water.
  • A rotating paddle agitates the mixture and draws air in it. As a result, the froth is formed which carries the mineral particles. The froth is light and is skimmed off. It is then dried for recovery of the ore particles.

Sometimes it is possible to separate two sulphide ores by adjusting the proportion of oil to water by using depressants. When a depressant $NaCN$ is added to an ore containing $ZnS$ and $PbS$, what is the correct observation?

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. $NaCN$ prevents $PbS$ from coming to the froth but allows $ZnS$ to come with froth

  2. $NaCN$ prevents $ZnS$ from coming to the froth but allows $PbS$ to come with froth

  3. $NaCN$ prevents frothing of both $ZnS$ and $PbS$, hence no froth is formed

  4. $NaCN$ does not act as depressant hence a mixture of $PbS$ and $ZnS$ is found in the froth

Show answer
Correct Option: B
Explanation:
  • Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water.
  • It is possible to separate two sulphide ores by adjusting the proportion of oil to water or by using ‘depressants’.
  •  In the 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.

The oil used as frothing agent in froth floatation process is:

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. coconut oil

  2. castor oil

  3. palmitic oil

  4. pine oil

Show answer
Correct Option: D
Explanation:
  • Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water.
  • Collectors and froth stabilizers are added to it. 
  • Collectors (e.g., pine oils, fatty acids, xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilizers (e.g., cresols, aniline) stabilize the froth. 
  • The mineral particles become wet by oils while the gangue particles by water.

Which of the following reactions does not take place during leaching for concentration of bauxite?

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. $Al _2O _3+2NaOH+3H _2O\rightarrow 2Na[Al(OH) _4]$

  2. $2Na[Al(OH) _4]+CO _2\rightarrow Al _2O _3.xH _2O+2NaHCO _3$

  3. $Al _2O _3.2H _2O\xrightarrow{{\Delta}}Al _2O _3+2H _2O$

  4. $Al _2O _3.xH _2O\xrightarrow{{\Delta}}Al _2O _3+xH _2O$

Show answer
Correct Option: C
Explanation:
  • Bauxite is the principal ore of aluminium.  The impurities present in bauxite are $SiO _2$, iron oxides and titanium oxide ($TiO _2$). 
  • Concentration is carried out by heating the powdered ore with a concentrated solution of NaOH at 473 – 523 K and 35 – 36 bar pressure. This process is called digestion. 
  •  $Al _2O _3$ is extracted out as sodium aluminate. The impurity, $SiO _2$ too dissolves forming sodium silicate. Other impurities are left behind.
$Al _2O _3+2NaOH+3H _2O \rightarrow 2Na[Al(OH) _4]$
  • The sodium aluminate present in solution is neutralised by passing $CO _2$ gas and hydrated $Al _2O _3$ is precipitated. At this stage, small amount of freshly prepared sample of hydrated$Al _2O _3$ is added to the solution. This is called seeding. It induces the precipitation.
$2Na[Al(OH) _4]+CO _2 \rightarrow Al _2O _3.xH _2O+2NaHCO _3$
  • Sodium silicate remains in the solution and hydrated alumina is filtered, dried and heated to give back pure$Al _2O _3$.
$Al _2O _3.xH _2O \rightarrow Al _2O _3 + xH _2O$

  • Hence, option C is correct answer.

Forth floatation process of concentration is based on the:

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. preferential wetting properties with the frothing agent and water

  2. difference in the specific gravities of gangue and ore particles

  3. difference in solubility of ganaue and ore particles in frothing agent and water

  4. difference in reactivity of gangue and ore particles with water and frothing agent.

Show answer
Correct Option: A
Explanation:
  • Froth floatation process method is used for removing gangue from sulphide ores.
  •  In this process, a suspension of the powdered ore is made with water. Collectors and froth stabilizers are added to it. 
  • Collectors (e.g., pine oils, fatty acids, xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilizers (e.g., cresols, aniline) stabilize the froth.
  • The mineral particles become wet by oils while the gangue particles by water. 

For which of the following ores forth floatation method is used for concentration?

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. Haematite

  2. Zinc blende

  3. Magnetite

  4. Carnallite

Show answer
Correct Option: B
Explanation:
  • Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water
  • Among the given options Zinc blend ($ZnS$) is the only sulphide ore and hence Froth floatation process is used for its concentration.
  • Hence, option B is the right answer.

Which of the following metals is not extracted by leaching?

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. Aluminium

  2. Mercury

  3. Silver

  4. Gold

Show answer
Correct Option: B
Explanation:

Leaching is a process where ore is soluble and impurities are insoluble, widely used extractive metallurgy technique which converts metals into soluble salts in aqueous media.
Bauxite, SIlver and gold ores are usually soluble in some solvents and hence leaching is used to concentrate them.
Hence, option $B$ is the correct answer.

Which of the following statements is correct about the role of collectors added during forth floatation process?

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. Collectors enhance the non-wettability of ore particles

  2. Collectors enhance the wettability of gangue particles

  3. Collectors help in separating two sulphide ores present in the mixture

  4. Collectors help ore particles to settle down below the froth

Show answer
Correct Option: A
Explanation:
  • Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water.
  • Collectors and froth stabilizers are added to it. Collectors (e.g., pine oils, fatty acids, xanthates, etc.) enhance non-wettability of the mineral particles and froth stabilizers (e.g., cresols, aniline) stabilize the froth.
  • The mineral particles become wet by oils while the gangue particles by water.

Which of the following ores is concentrated by chemical leaching method?

chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

  1. Cinnabar

  2. Argentite

  3. Copper pyrites

  4. Galena

Show answer
Correct Option: B
Explanation:
  • In the metallurgy of silver , the respective metal is eached with a dilute solution of NaCN or KCN in the presence of air, which supplies $O _2$. The metal is obtained later by replacement reaction.
  • The reactions involved are-
$4Ag+8CN^{-}+2H _2O+O _2 \rightarrow 4[M(CN) _2]^{-}+4OH^{-}$

$2[Ag(CN) _2]^{-}+Zn \rightarrow [Zn(CN) _4]^{2-}+2Ag$
  • Hence, Argentite being an ore of SIlver is concenrated by leaching.