This set of Extractive Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Leaching Reagents and Techniques”.
1. Why are the ores crushed and ground before reacting it with leaching reagents?
a) To reduce the surface area of particles
b) To increase the surface area of particles
c) To reduce the reaction rate
d) To increase the number of particles
View Answer
Explanation: Usually the ores are crushed and ground before reacting it with leaching reagents. This increases the surface area of particles. This will help to increase the reaction rate. Sometimes before reacting with leaching reagents, some chemical treatments are done beforehand.
2. Which of the following factors is not necessary while choosing a suitable leaching reagent?
a) Cost of reagent
b) Regeneration ability of reagent
c) Corroding properties of the reagent
d) Colour of reagent
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Explanation: A leaching reagent is chosen to take into account some of the important factors like cost of reagent, regeneration ability, corrosion ability, selectivity etc. Colour of the reagent does not have much role in the choice of the reagent. While choosing a reagent, we have to also depend on the physical and chemical properties of the material which is to be leached.
3. What is the process called in which the desirable elements are dissolved in a reagent selectively, during a hydrometallurgy process?
a) Leaching
b) Lynching
c) Leach liquoring
d) Separation of leach liquor
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Explanation: Leaching is the first step during a hydrometallurgy process. In leaching, desired elements are dissolved selectively, in a suitably chosen leaching reagent. Sometimes, we conduct some preliminary steps before leaching such as crushing, grinding, roasting etc. for the proper conduct of the whole process.
4. Which of the following process is not done for the separation of leach liquor?
a) Electrolysis
b) Washing
c) Filtration
d) Settling
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Explanation: During the separation of leach liquor, it is separated from the residues in solid form, after leaching, by using one or more methods. Some of the methods are settling, thickening, filtration etc. Electrolysis is a method used in electrometallurgy.
5. Which of the following can be used as a leaching reagent?
a) Wax
b) Carbon electrode
c) Acids
d) Glass
View Answer
Explanation: Leaching reagents are chosen such that the ores can be selectively dissolved in it. These reagents are chemicals which helps to attain an oxidized or reduced state of a metal compound. So, the common leaching reagents which can be used are water, acids, bases, aqueous salt solutions etc.
6. It is very difficult to dissolve CuSO4 in water.
a) True
b) False
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Explanation: Most of the compounds of alkali metals are easy to dissolve in water. Some of which are CuSO4, ZnSO4 etc. If we heat these solutions then, we can also accelerate the leaching process. The use of water as a leaching reagent is very rare commercially.
7. Which of the following situation of acid will attack strongly on the ores and minerals during the leaching process?
a) Concentrated
b) Dilute
c) Cold
d) Reddish colour
View Answer
Explanation: Minerals and ores will dissolve readily into the solution, during the leaching process, if the acids are concentrated and hot. The most commonly used acid for the leaching process is sulphuric acid. When we use sulphuric acid as a leaching reagent then we do not need fine grinding.
8. What is the result of ammonia leaching?
a) Acid
b) Base
c) Insoluble solid phase
d) Complex ion
View Answer
Explanation: Ammonia is an alkali leaching reagent. The most common alkali used for the leaching process is NaOH. While using ammonia for leaching, mostly there is a formation of a complex ion. This can be illustrated using following reaction: CuO + 2NH4+ + 2NH3 = Cu (NH3)42+ + H2O.
9. Why is the preliminary grinding for the leaching process done in the presence of water?
a) To change its state
b) To accelerate the grinding process
c) To reduce dust losses
d) To obtain large chunks of ore
View Answer
Explanation: Generally, the preliminary grinding for the leaching process is done in the presence of water to reduce the dust losses. The product obtained after this process is called the pulp. This product has around 40-70% solid. Using pulp, we can make the leaching process very effective.
10. Which of the following is not a leaching technique?
a) In situ leaching
b) Heap leaching
c) Dump leaching
d) Dissolution leaching
View Answer
Explanation: Dissolution leaching is not a leaching technique. There are several leaching techniques which are used commercially. The common leaching techniques are In situ leaching, heap leaching and percolation leaching. The traditional leaching techniques can treat the ores at the mine itself.
11. In which leaching technique, stirring is used to help the dissolution process?
a) Agitation leaching
b) Dump leaching
c) Heap leaching
d) Percolation leaching
View Answer
Explanation: In the agitation leaching technique, stirring is used to help the dissolution process. There may be variations in this technique like in pressure, current modes and stages.
12. In situ leaching is direct leaching of the ore deposits.
a) True
b) False
View Answer
Explanation: In situ leaching can be in two ways. It can be the direct leaching of the ore deposits. It can also be the leaching of the residue rocks left behind in the mines after the mining operation. This type of leaching operation employs water circulation through ore deposits and then the collection of the solution.
13. In which type of leaching, the ores are left exposed to atmospheric moisture?
a) In situ leaching
b) Heap leaching
c) Agitation leaching
d) Percolation leaching
View Answer
Explanation: In heap leaching, the ores are placed above the ground level, in a predetermined manner, using dumps. These heaps are left exposed to atmospheric moisture and natural rain. In this type of leaching technique, higher grade of ores are leached.
14. What is the advantage of using percolation leaching technique?
a) Batches are identical
b) Less water is used
c) High Operational flexibility
d) Low Operational flexibility
View Answer
Explanation: Percolation leaching is done in batches in a tank. Each batch is separate and distinct which gives us high operational flexibility. This technique is more versatile compared to others. This technique can also be employed where the leaching rate is slow.
Sanfoundry Global Education & Learning Series – Extractive Metallurgy.
To practice all areas of Extractive Metallurgy, here is complete set of Multiple Choice Questions and Answers.
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