This set of Extractive Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Leaching Kinetics”.
1. Most of the leaching reactions are reversible.
a) True
b) False
View Answer
Explanation: The statement is incorrect. Most of the reactions in the leaching process are irreversible. This is the reason that the thermodynamics of the leaching process is not considered so important. The reactions of the leaching process take place far away from equilibrium.
2. What happens when a mineral dissolves only in a part of the leaching reagent?
a) Solid residue appears
b) Solid residue disappears
c) Rest of the solution gets evaporated
d) The solution changes its colour
View Answer
Explanation: Usually in the case of incomplete dissolution of the mineral in the leaching reagent, there is a formation of a new solid residue. When this phase is porous then the leaching would not stop and continue.
3. How can we increase the rate of dissolution of the leaching reaction at the interface?
a) By decreasing the temperature
b) By increasing the size of the particle
c) By using dilute reagents
d) By increasing the surface area of the particles
View Answer
Explanation: We can increase the dissolution rate at the interface of the leaching reaction so that the dissolution gets completed. This can be done by increasing the temperature, by using more concentrated reagents and by increasing the surface area of the particles.
4. Which of the following conditions under pressure leaching can accelerate the leaching process?
a) Low pressure
b) High pressure
c) Very low concentration of ammonia gas
d) Low temperature
View Answer
Explanation: When pressure higher than the atmospheric pressure is applied then, the boiling point of water increases which makes high temperature available to the leaching process. This will help in increasing the leaching rate of the reaction.
5. A high concentration of ammonia gas will decrease the leaching rate.
a) True
b) False
View Answer
Explanation: The statement is incorrect. The leaching rate of the reaction can be enhanced by adding ammonia or oxygen gas. The concentration of these gases increases with the increasing pressure which increases the leaching rate.
6. How do bacteria grow on pure inorganic media?
a) By reducing inorganic substances
b) By reproduction
c) By oxidizing inorganic substances
d) By collision
View Answer
Explanation: Some bacteria are capable of accelerating a leaching reaction. These bacteria are capable of growing on a pure inorganic media by oxidizing the inorganic substances like sulphur and ferrous ions. These bacteria increase the rate of dissolution of a reaction.
7. Which of the following is true for electrons produced during dissolution when the solid is electronically conducting?
a) Restricted to a particular location
b) Free to move through the solid
c) Can be broken further
d) Not free to move through the solid
View Answer
Explanation: The electrons produced during the oxidation of metallic compounds or dissolution are free to move through the solid and not restricted to a particular location when the solid is electronically conducting. These electrons can be released to an oxidizing media anywhere on the surface like galvanic corrosion of metal.
8. Which of the following is the correct Arrhenius equation?
a) ln K = ln A – (ΔE/RT)
b) ln K = ln A + (ΔE/RT)
c) ln K = (ΔE/RT) – ln A
d) d ln K = (ΔE/RT). dT
View Answer
Explanation: The correct form of Arrhenius Equation is ‘ln K = ln A – (ΔE/RT)’, where ΔE = experimental activation energy, T = absolute temperature and K = rate constant of the reaction. This equation is usually used to express the effect of temperature on the rate of leaching.
9. During dissolution, when the electrons are released to the oxidizing medium, what is the area called which gets oxidized?
a) Cathodic area
b) Reducing area
c) Anodic area
d) Corrosion area
View Answer
Explanation: During dissolution, a specific number of electrons produced are released to the oxidizing medium. These electrons are free to move and are released anywhere on the surface. The area which is oxidized is called an anodic area.
10. The equilibrium of the cyanidation process would depend on which of the following?
a) The partial pressure of nitrogen
b) The partial pressure of hydrogen
c) The partial pressure of ozone
d) The partial pressure of oxygen
View Answer
Explanation: Oxygen has an important role in the leaching operations. It is involved as a reactant in the process. The reaction of the cyanidation process for the dissolution of gold and silver cannot be reached unless there is oxygen present in the reaction. The equilibrium depends on the partial pressure of oxygen.
11. In which of the following leaching process does oxygen have an indirect role?
a) Bacterial leaching
b) Pressure leaching
c) Cyanidation process
d) Leaching of Chalcopyrite
View Answer
Explanation: In some of the leaching processes, oxygen plays an indirect role like bacterial leaching. In this type of leaching, microorganisms serve as a catalyst. These organisms need oxygen for survival. So, in the absence of oxygen during bacterial leaching, the catalytic activity would not work.
12. Which of the following can accelerate the rate of gas absorption?
a) Decreasing partial pressure of the gas
b) Decreasing moles of gas
c) Increasing agitation efficiency
d) Increasing partial pressure of the liquid
View Answer
Explanation: We can accelerate the rate of absorption of gas by increasing agitation efficiency. Rate of gas absorption can also be accelerated by increasing partial pressure of a liquid and by increasing the gas-liquid interface.
13. What is the biological catalyst called which is synthesized by bacteria?
a) Ferrobacillus
b) Thiobacillus
c) Hormone
d) Enzyme
View Answer
Explanation: Enzyme is the biological catalyst which is synthesized by bacteria during the leaching operation. This catalyst helps in accelerating the rate of the oxidation reaction. Bacterial leaching also helps in a greater extent of recovery.
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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