chemistry : class12 Gangue and Mineral Separation : Concentration of ores : General Principles and Processes of Isolation of Elements MCQ Questions and Answers
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Gangue and Mineral Separation
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MCQ Questions
1. In froth flotation of a sulphide ore, the primary purpose of adding a collector such as xanthate is to:
A.
Increase the density of the gangue particles
B.
Make the sulphide mineral particles water-repellent
C.
Dissolve the sulphide mineral selectively in water
D.
Convert the gangue into a magnetic substance
Correct Answer:
Make the sulphide mineral particles water-repellent
Explanation:
Collectors selectively adsorb on sulphide mineral surfaces and impart hydrophobicity. The treated mineral particles attach to air bubbles and rise with the froth, while hydrophilic gangue remains in the aqueous phase.
2. A mixture contains a magnetic ore and non-magnetic gangue of comparable particle size and density. Which concentration method is most appropriate?
A.
Hydraulic washing
B.
Froth flotation
C.
Magnetic separation
D.
Hand picking
Correct Answer:
Magnetic separation
Explanation:
Magnetic separation depends on the difference in magnetic properties between the ore and gangue. It is especially suitable when differences in density or particle size cannot be used effectively.
3. During hydraulic washing, the separation of ore from gangue is mainly based on the difference in their:
A.
Electrical conductivities
B.
Densities
C.
Magnetic susceptibilities
D.
Solubilities in the collecting liquid
Correct Answer:
Densities
Explanation:
In hydraulic washing, a stream of water carries away the lighter gangue while the denser ore particles settle. Thus, the process relies mainly on the density difference between the ore and gangue.
4. In froth flotation, pine oil is commonly added because it primarily acts as a:
A.
Depressant for all sulphide minerals
B.
Frother that stabilizes the froth
C.
Magnetizing agent for the gangue
D.
Reducing agent for the mineral particles
Correct Answer:
Frother that stabilizes the froth
Explanation:
Pine oil lowers the surface tension and helps produce a stable froth. The hydrophobic mineral particles attached to air bubbles are carried into this froth for separation from gangue.
5. A collector is added in excess during the froth flotation of a sulphide ore. What is the most likely undesirable consequence?
A.
The ore becomes completely soluble in water
B.
The selectivity of mineral attachment may decrease
C.
The density difference between ore and gangue becomes zero
D.
The gangue particles become permanently magnetic
Correct Answer:
The selectivity of mineral attachment may decrease
Explanation:
An excessive amount of collector can cause unwanted particles, including some gangue or other minerals, to become hydrophobic. This reduces the selective nature and purity of the separation.
6. In selective froth flotation of a mixture of two sulphide minerals, a depressant is used to:
A.
Prevent one selected mineral from attaching to air bubbles
B.
Increase the density of the desired mineral
C.
Convert both minerals into oxides
D.
Make the gangue particles magnetic
Correct Answer:
Prevent one selected mineral from attaching to air bubbles
Explanation:
A depressant selectively suppresses the flotation of one sulphide mineral while allowing the desired mineral to remain hydrophobic and float. This enables separation of minerals with similar physical properties.
7. Which condition is essential for effective froth flotation of a sulphide ore but not required in the same way for hydraulic washing?
A.
The ore must contain particles denser than the gangue
B.
The mineral surface must be selectively rendered hydrophobic
C.
The gangue must have a different magnetic response
D.
The ore must be separated only by particle size
Correct Answer:
The mineral surface must be selectively rendered hydrophobic
Explanation:
Froth flotation requires selective hydrophobicity so that mineral particles attach to air bubbles. Hydraulic washing instead uses a flowing liquid and mainly depends on differences in density.
8. An ore contains a non-magnetic mineral finely interlocked with magnetic gangue. Which preliminary operation would most improve the effectiveness of magnetic separation?
A.
Grinding the ore to liberate the particles
B.
Adding a frother without water
C.
Increasing the moisture content without size reduction
D.
Coating all particles with a collector
Correct Answer:
Grinding the ore to liberate the particles
Explanation:
Comminution liberates the mineral and gangue particles that are physically locked together. Once liberated, their different magnetic responses can be used effectively for separation.
9. A powdered ore is washed with water, and the valuable mineral settles while finely divided gangue is carried away. This observation indicates that the valuable mineral is:
A.
Less dense than the gangue
B.
More dense than the gangue
C.
More magnetic than the gangue
D.
More soluble than the gangue
Correct Answer:
More dense than the gangue
Explanation:
In hydraulic washing, denser particles settle more readily, whereas lighter particles are swept away by the water stream. The settling behavior therefore indicates that the valuable mineral has greater density.
10. Why is crushing and grinding usually performed before applying a physical method of ore concentration?
A.
To convert every mineral into a gas
B.
To liberate ore particles from the surrounding gangue
C.
To remove the need for any separation method
D.
To make all particles identical in density
Correct Answer:
To liberate ore particles from the surrounding gangue
Explanation:
Crushing and grinding reduce the ore to a size at which valuable mineral particles become detached from gangue. Liberation is necessary so that differences in density, magnetism, or surface properties can be used for separation.
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