Tag: concentration of ore

Questions Related to concentration of ore

What is the process of leaching in case of low grade copper ores?

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

  1. Leaching is carried out with $NaOH$ and $O _2$

  2. Leaching is carried out with $NaCN$

  3. Leaching is carried out with acids in presence of $O _2$

  4. Leaching is carried out by boiling the ore with water

Show answer
Correct Option: C
Explanation:

Leaching of low grade copper ores is carried out with acid or bacteria, when copper goes into solution as $Cu^{2+} _{(aq) }+ H _{2(g)}\rightarrow Cu _{(s)}+2H^+ _{(aq)}$ 

How do we separate two sulphide ores by froth floatation method?

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

  1. By using excess of pine oil.

  2. By adjusting proportion of oil to water or using depressant.

  3. By using collectors and froth stabilities like xanthates.

  4. By using some solvent in which one of the sulphides is soluble.

Show answer
Correct Option: B
Explanation:

By using depressants or adjusting proportion of oil to water, selective prevention of one sulphide ore from coming to the froth is possible.

An ore of tin containing, $FeCrO _4$ is concentrated by:

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

  1. gravity separation

  2. magnetic separation

  3. forth floatation

  4. leaching

Show answer
Correct Option: B
Explanation:
  • Magnetic separation based on differences in magnetic properties of the ore components.
  •  If either the ore or the gangue is attracted towards the magnetic field, then the separation is carried out by this method. 
  • For example, iron ores are attracted towards the magnet, hence, non–magnetic impurities can be separated from them using magnetic separation.
  • Here,$FeCrO _4$ being an iron ore can be separated by magnetic separation.

Removal of the unwanted materials like sand, clays, etc. from the ore is known as __, ___ or _____.

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

  1. concentration, dressing, benefaction

  2. separation, refining, gangue

  3. magnetic separation, Purification, gangue

  4. washing, refining, amalgamation

Show answer
Correct Option: A
Explanation:
  • Removal of the unwanted materials (e.g., sand, clays, etc.) from the ore is known as concentration, dressing or benefaction.

  • Before proceeding for concentration, ores are graded and crushed to a reasonable size. 

  • The concentration of ores involves several steps and the selection of these steps depends upon the differences in physical properties of the compound of the metal present and that of the gangue.

Which of the following ores cannot be concentrated by magnetic separation?

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

  1. Haematite

  2. Malachite

  3. Magnetite

  4. Siderite

Show answer
Correct Option: B
Explanation:
  • Magnetic separation based on differences in magnetic properties of the ore components.
  •  If either the ore or the gangue is attracted towards the magnetic field, then the separation is carried out by this method. 
  • For example, iron ores are attracted towards the magnet, hence, non–magnetic impurities can be separated from them using magnetic separation.
  • Here, Haematite, Magnetite, and Sidderite are iron ores and hence magnetic separation can be used to separate them.
  • Malachite is a Copper ore and hence magnetic separation can't be used to concentrate it.

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.