chemistry : class12 Hand Picking : Concentration of ores : General Principles and Processes of Isolation of Elements MCQ Questions and Answers
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Hand Picking
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MCQ Questions
1. A run-of-mine sample contains large, liberated lumps of a copper mineral that are visibly green, mixed with grey siliceous gangue. Which condition most directly justifies concentration by hand picking?
A.
The mineral and gangue have identical colour but different densities
B.
The valuable mineral occurs as visibly distinct particles from the gangue
C.
The mineral is present as a finely disseminated coating on gangue
D.
The ore particles are too small to be individually observed
Correct Answer:
The valuable mineral occurs as visibly distinct particles from the gangue
Explanation:
Hand picking is effective when ore and gangue occur as sufficiently large, liberated pieces with an observable difference, such as colour or appearance, allowing unwanted material to be manually removed.
2. Why is hand picking generally unsuitable for an ore in which the valuable mineral is uniformly disseminated as microscopic grains throughout the gangue?
A.
Hand picking cannot exploit differences that are not visually discernible in individual particles
B.
Hand picking requires the ore to be dissolved before separation
C.
Hand picking separates only substances having different magnetic properties
D.
Hand picking is restricted to ores containing metallic minerals only
Correct Answer:
Hand picking cannot exploit differences that are not visually discernible in individual particles
Explanation:
Hand picking depends on the operator recognizing and physically removing distinct ore or gangue particles. Microscopic or finely disseminated grains cannot normally be selected individually by visual inspection.
3. An ore is crushed until each visible lump contains either mostly valuable mineral or mostly gangue, but further crushing would produce indistinguishable fine fragments. For hand picking, the best interpretation is that the ore has reached:
A.
A particle size at which useful liberation is achieved without excessive fines
B.
A particle size at which magnetic separation becomes compulsory
C.
A particle size at which chemical extraction has already occurred
D.
A particle size at which density differences disappear
Correct Answer:
A particle size at which useful liberation is achieved without excessive fines
Explanation:
Hand picking benefits from adequate liberation into visible pieces. Excessive crushing may create fine particles that are difficult to inspect and handle, whereas insufficient crushing leaves ore and gangue locked together.
4. In manual concentration by hand picking, which material is most commonly removed by the picker when the valuable mineral is visually distinctive and present in relatively high proportion?
A.
The visible gangue pieces surrounding the valuable mineral
B.
The chemically dissolved valuable mineral
C.
The invisible mineral inclusions inside each gangue grain
D.
The valuable mineral after it has been converted into a gas
Correct Answer:
The visible gangue pieces surrounding the valuable mineral
Explanation:
In hand picking, the operator can remove either gangue or ore depending on which is easier to recognize and which is present in smaller quantity. When the valuable mineral is distinctive and abundant, removing visible gangue is commonly more practical.
5. Two ore samples have the same average grade. Sample P consists of coarse, clearly distinguishable ore and gangue lumps, whereas Sample Q contains finely intergrown particles. Which sample is more suitable for hand picking, and why?
A.
Sample P, because visual recognition and physical removal of liberated pieces are possible
B.
Sample P, because hand picking works only when the ore has the lower density
C.
Sample Q, because fine intergrowth increases the number of particles available for selection
D.
Sample Q, because hand picking requires intimate contact between ore and gangue
Correct Answer:
Sample P, because visual recognition and physical removal of liberated pieces are possible
Explanation:
The suitability of hand picking depends primarily on visible differentiation and liberation, not merely on average grade. Coarse, distinct lumps can be selected manually, unlike finely intergrown particles.
6. A hand-picking operation removes waste rock from an ore stream. Which change would most directly reduce the reliability of this operation?
A.
Increasing the colour contrast between ore and waste
B.
Presenting the feed as a thin, well-spread layer
C.
Allowing dust and fine particles to cover the visible surfaces of the lumps
D.
Using previously crushed, liberated lumps of moderate size
Correct Answer:
Allowing dust and fine particles to cover the visible surfaces of the lumps
Explanation:
Hand picking requires clear visual identification. Dust or adhering fines can obscure the distinguishing features of ore and gangue, making manual selection less accurate.
7. Which ore-feed arrangement would provide the most favourable conditions for selective hand picking?
A.
A thick, rapidly moving heap containing overlapping particles
B.
A thin layer of coarse, liberated particles moving slowly enough for inspection
C.
A slurry containing suspended microscopic mineral grains
D.
A sealed container in which particles cannot be visually examined
Correct Answer:
A thin layer of coarse, liberated particles moving slowly enough for inspection
Explanation:
Effective hand picking requires each particle to be accessible and visible. A thin, slowly presented layer minimizes overlap and gives the operator enough opportunity to distinguish and remove selected pieces.
8. Hand picking is most likely to be economically preferred over more elaborate concentration methods when the ore:
A.
Contains abundant, visually recognizable waste pieces that can be removed with little processing
B.
Contains valuable mineral grains that are completely invisible to the eye
C.
Requires complete liberation by extremely fine grinding
D.
Has ore and gangue particles with no observable difference
Correct Answer:
Contains abundant, visually recognizable waste pieces that can be removed with little processing
Explanation:
Hand picking is a simple and low-cost method when coarse, visibly identifiable material can be separated directly. It becomes unsuitable when fine grinding or subtle, non-visible differences are required.
9. A mineral processing engineer proposes hand picking for a low-grade ore in which the gangue occurs as large, easily recognizable fragments, while the valuable mineral is distributed in small but visually detectable pieces. What is the principal limitation of this proposal?
A.
Removing gangue manually may involve handling a very large mass of waste for relatively little valuable mineral
B.
Hand picking cannot remove gangue; it can remove only the valuable mineral
C.
Hand picking always changes the chemical composition of the selected mineral
D.
Hand picking is impossible whenever gangue fragments are larger than ore fragments
Correct Answer:
Removing gangue manually may involve handling a very large mass of waste for relatively little valuable mineral
Explanation:
Although visible separation may be possible, hand picking is labour-intensive and becomes inefficient when a low-grade ore requires removal of a large quantity of gangue to recover a small amount of valuable mineral.
10. Which statement best distinguishes hand picking from a separation method based on a physical property such as magnetism or density?
A.
Hand picking uses direct visual recognition and manual removal of selected particles
B.
Hand picking requires a reagent to react selectively with the gangue
C.
Hand picking separates particles only according to their boiling points
D.
Hand picking depends on creating an electric field between ore particles
Correct Answer:
Hand picking uses direct visual recognition and manual removal of selected particles
Explanation:
Hand picking is a visual, manual concentration method. Its selectivity comes from the observable appearance of individual ore and gangue pieces rather than from magnetic, density, electrical, or chemical differences.
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