This set of Extractive Metallurgy Multiple Choice Questions & Answers (MCQs) focuses on “Pyrometallurgical Processes under Low or High Pressures”.
1. How metals like Titanium and Zirconium simulate vacuum processing?
a) High affinity for Hydrogen and Nitrogen
b) Low affinity for Hydrogen and Nitrogen
c) Easy availability of these metals
d) Due to their high melting point
View Answer
Explanation: Metals like Titanium, Zirconium, and Germanium etc. easily combines with hydrogen and nitrogen at high temperatures. This property of these metals simulates processes using a vacuum.
2. Which of the following is not a low-pressure process?
a) Thermal dissociation
b) Thermal reduction
c) Sublimation
d) Condensation
View Answer
Explanation: In a low-pressure process, metal in a solid or liquid state is reduced to a gaseous, solid or liquid acid radical. In condensation, it is somewhat opposite. In the condensation process, the conversion of gas to liquid takes place. Low-pressure processes are classified into three types: thermal dissociation, thermal reduction and sublimation.
3. How does vacuum help when a process takes place?
a) By increasing the pressure
b) By increasing the temperature
c) By eliminating one of the reaction products
d) By decreasing the temperature of the reaction
View Answer
Explanation: If we change the pressure we can shift the equilibrium of a reaction. When we operate in a vacuum, it helps in eliminating a reaction product which can be easily evaporated at normal temperatures. It drives the reaction towards its completion.
4. Thermal decomposition of oxides is can be easily processed under vacuum.
a) True
b) False
View Answer
Explanation: The statement is not correct. Thermal decomposition of oxides requires a very high temperature and degree of vacuum for metal extraction to take place. So, it is not possible to thermally decompose oxides under vacuum. Though there are some exceptions like silver and mercury whose oxides are not so stable.
5. What is the temperature and pressure at which the following reaction can be performed under vacuum?
2MgO.CaO + 1/6(FeSi6) → 2Mg (g) + 1/6Fe + 2CaO.SiO2
a) 200°C and 1mm Hg
b) 1100°C and 1mm Hg
c) 500°C and 5mm Hg
d) 2500°C and 20mm Hg
View Answer
Explanation: As the reaction is taking place in vacuum the pressure should be very low. Also, for the reduction of metal oxide to take place the temperature should be high. So, the correct answer is 1100°C temperature and about 1mm Hg pressure.
6. Complete the following reaction which is taking place under vacuum.
LiOH + Al + CaO → ______ + 3CaO.Al2O3 + H2 [Pressure: 1mm Hg, Temperature: 1050°C]
a) Li
b) Li2O
c) CaO
d) Ca
View Answer
Explanation: The above-shown reaction is aluminothermic reduction reaction for Lithium hydroxide. The process takes place under very low pressure. The product lithium is formed in a gaseous state. The complete balanced reaction is: 6LiOH + 4Al + 6CaO → 6Li (g) + 2(3CaO.Al2O3) + 3H2 (g).
7. It is impossible to remove oxygen from molten steel.
a) True
b) False
View Answer
Explanation: The statement is not correct. We know that gases entrapped in the molten steel can defect the product. So, we can use the application of vacuum to remove these gases. For example, the reaction [C] + [O] = CO (g), remove oxygen from the molten steel.
8. What is the condition to favour the high-pressure reactions?
a) The reaction should be endothermic
b) The reaction should be exothermic
c) Net volume of the system should increase
d) Net volume of the system should decrease
View Answer
Explanation: High-pressure reactions are not so popular commercially. To favour a high-pressure reaction, the consumption of the number of moles in the gaseous phase should be more than the generated number of moles. Therefore, the net volume of the system should decrease.
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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