chemistry : class12 Sulfide Ore Concentration : Concentration of ores : General Principles and Processes of Isolation of Elements MCQ Questions and Answers
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Sulfide Ore Concentration
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MCQ Questions
1. In the froth flotation concentration of a sulphide ore, the primary function of a collector such as potassium ethyl xanthate is to:
A.
Convert the sulphide mineral into its oxide
B.
Make the sulphide mineral surface water-repellent
C.
Increase the density of the gangue particles
D.
Dissolve the sulphide mineral selectively in water
Correct Answer:
Make the sulphide mineral surface water-repellent
Explanation:
A collector adsorbs on the sulphide mineral surface and imparts hydrophobicity, allowing the mineral particles to attach to air bubbles and rise with the froth.
2. Why is pine oil added during the froth flotation of sulphide ores?
A.
It acts as a depressant for all sulphide minerals
B.
It increases the solubility of the gangue in water
C.
It stabilizes the froth formed by air bubbles
D.
It converts sulphide ions into sulphate ions
Correct Answer:
It stabilizes the froth formed by air bubbles
Explanation:
Pine oil functions as a frother. It helps produce and stabilize a persistent froth that carries the hydrophobic sulphide mineral particles to the surface.
3. In the selective flotation of a mixture of galena and zinc blende, which reagent is commonly used to depress zinc blende while galena is floated?
A.
Sodium cyanide
B.
Copper sulphate
C.
Pine oil
D.
Potassium ethyl xanthate
Correct Answer:
Sodium cyanide
Explanation:
Sodium cyanide acts as a depressant for zinc blende under suitable conditions, preventing its attachment to air bubbles while galena is selectively floated.
4. During the selective concentration of zinc blende after galena has been removed, copper sulphate is added mainly to:
A.
Depress galena permanently
B.
Activate the surface of zinc blende
C.
Dissolve the froth-producing oil
D.
Increase the quantity of siliceous gangue
Correct Answer:
Activate the surface of zinc blende
Explanation:
Copper sulphate activates zinc blende by producing a copper-containing surface layer, which enables the collector to adsorb more effectively and promotes flotation.
5. A sulphide mineral remains in the aqueous pulp instead of rising with the froth during flotation. Which surface property is most likely responsible?
A.
The mineral particles are sufficiently hydrophobic
B.
The mineral particles have become preferentially wetted by water
C.
The particles have adsorbed an effective collector layer
D.
The particles are strongly attached to air bubbles
Correct Answer:
The mineral particles have become preferentially wetted by water
Explanation:
Flotation requires hydrophobic particles. If a sulphide mineral surface is wetted by water, it does not attach effectively to air bubbles and remains in the pulp.
6. Which sequence most accurately represents the essential events in froth flotation of a sulphide ore?
A.
Calcination, reduction, melting, and crystallization
B.
Grinding, collector adsorption, bubble attachment, and froth separation
C.
Dissolution, filtration, evaporation, and sublimation
D.
Roasting, chlorination, hydrolysis, and precipitation
Correct Answer:
Grinding, collector adsorption, bubble attachment, and froth separation
Explanation:
The ore is finely ground, the collector selectively modifies the mineral surface, hydrophobic particles attach to air bubbles, and the mineral-rich froth is separated from the gangue.
7. The effectiveness of a collector in sulphide ore flotation depends most directly on its ability to:
A.
Increase the melting point of the ore
B.
Form a preferentially adsorbed hydrophobic layer on the sulphide mineral
C.
React equally with mineral and gangue surfaces
D.
Convert all particles into colloidal solution
Correct Answer:
Form a preferentially adsorbed hydrophobic layer on the sulphide mineral
Explanation:
Selective flotation occurs when the collector adsorbs preferentially on the sulphide mineral and makes its surface hydrophobic without similarly affecting the gangue.
8. In a flotation cell, excessive froth stability can reduce the selectivity of concentration because it may:
A.
Prevent all air bubbles from forming
B.
Cause unwanted gangue particles to be carried into the froth
C.
Make every sulphide particle hydrophilic
D.
Destroy the collector by converting it into water
Correct Answer:
Cause unwanted gangue particles to be carried into the froth
Explanation:
An excessively persistent froth can mechanically entrap or carry gangue particles, lowering the purity of the sulphide concentrate even though flotation of the mineral occurs.
9. Why is fine grinding important before the froth flotation of a sulphide ore?
A.
It exposes mineral surfaces and liberates sulphide particles from gangue
B.
It converts the sulphide directly into a metal
C.
It makes the gangue chemically identical to the ore mineral
D.
It eliminates the need for a collector and a frother
Correct Answer:
It exposes mineral surfaces and liberates sulphide particles from gangue
Explanation:
Fine grinding increases liberation of sulphide mineral particles from gangue and provides fresh surfaces on which collectors can adsorb selectively.
10. Which change would most likely improve the selectivity of flotation when a depressant is used for a particular sulphide mineral?
A.
Using a reagent that suppresses the flotation of that mineral while leaving the desired mineral hydrophobic
B.
Adding a frother that wets every particle completely
C.
Increasing the amount of gangue in the feed
D.
Removing all air bubbles from the flotation pulp
Correct Answer:
Using a reagent that suppresses the flotation of that mineral while leaving the desired mineral hydrophobic
Explanation:
A depressant improves selective concentration by preventing a particular mineral from attaching to bubbles, while the desired sulphide mineral continues to float with the collector and froth.
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