Tag: principles of metallurgy
Questions Related to principles of metallurgy
Removal of the unwanted materials like sand, clays, etc. from the ore is known as __, ___ or _____.
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concentration, dressing, benefaction
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separation, refining, gangue
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magnetic separation, Purification, gangue
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washing, refining, amalgamation
- 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.
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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?
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Haematite
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Malachite
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Magnetite
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Siderite
- 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:
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it helps to remove the impurities like $SiO _2, Fe _2O _3,$ etc from the bauxite ore
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it converts the ore into oxide
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it reduces melting point of the ore
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it eliminates water from bauxite.
- Bauxite is the principal ore of aluminium. The impurities present in bauxite are $SiO _2$, iron oxides and titanium oxide ($TiO _2$).
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$Al _2O _3$ is extracted out as sodium aluminate. The impurity, $SiO _2$ too dissolves forming sodium silicate. Other impurities are left behind.
- 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:
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forth floatation
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electromagnetic process
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gravity process
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distillation
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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
- 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?
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$NaCN$ prevents $PbS$ from coming to the froth but allows $ZnS$ to come with froth
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$NaCN$ prevents $ZnS$ from coming to the froth but allows $PbS$ to come with froth
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$NaCN$ prevents frothing of both $ZnS$ and $PbS$, hence no froth is formed
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$NaCN$ does not act as depressant hence a mixture of $PbS$ and $ZnS$ is found in the froth
- 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:
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coconut oil
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castor oil
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palmitic oil
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pine oil
- 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.
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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?
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$Al _2O _3+2NaOH+3H _2O\rightarrow 2Na[Al(OH) _4]$
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$2Na[Al(OH) _4]+CO _2\rightarrow Al _2O _3.xH _2O+2NaHCO _3$
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$Al _2O _3.2H _2O\xrightarrow{{\Delta}}Al _2O _3+2H _2O$
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$Al _2O _3.xH _2O\xrightarrow{{\Delta}}Al _2O _3+xH _2O$
- 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.
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$Al _2O _3$ is extracted out as sodium aluminate. The impurity, $SiO _2$ too dissolves forming sodium silicate. Other impurities are left behind.
- 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.
- Sodium silicate remains in the solution and hydrated alumina is filtered, dried and heated to give back pure$Al _2O _3$.
- Hence, option C is correct answer.
Forth floatation process of concentration is based on the:
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preferential wetting properties with the frothing agent and water
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difference in the specific gravities of gangue and ore particles
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difference in solubility of ganaue and ore particles in frothing agent and water
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difference in reactivity of gangue and ore particles with water and frothing agent.
- 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?
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Haematite
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Zinc blende
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Magnetite
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Carnallite
- 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?
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Aluminium
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Mercury
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Silver
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Gold
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.