6.1. Which of the ores listed above may be concentrated by magnetic separation?
Ans. The magnetic separation method can be used to separate magnetic ore from non-magnetic gangue particles. Magnetic separation can be used to separate magnetic iron ores such as hematite (Fe2O3), magnetite (Fe3O4), siderite (FeCO3), and iron pyrites (FeS2) from non-magnetic silica and other impurities.
6.2. What significance does leaching serve in the extraction of aluminium?
Ans: Leaching or chemical separation is a very effective way to cleanse bauxite, an aluminium ore with iron oxide impurities. The impurities are removed from the ore by leaching it with a concentrated solution of NaOH to generate a soluble complex.
6.3 The reaction, is thermodynamically feasible as is apparent from the Gibbs energy value. Why does it not take place at room temperature?
Ans: The equilibrium constant, Keq, has been used to explain this. Since all reactants and products are solids at room temperature in the given redox reaction, there is no equilibrium between them, thus the reaction does not occur at RT. Cr melts at high temperatures, and TAS values rise. As a result, the value of becomes more negative, and hence reaction proceeds rapidly.
6.4. Is it true that Mg can reduce Al203 and Al can reduce MgO under specific conditions? What are those circumstances?
Ans. Yes, below 1350 °C Mg can reduce to Al203 and above 1350 °C. Al can reduce MgO. This can be inferred from ΔG° vs T plots.
Fig. Gibbs energy (ΔG°) vs T plots for formation of some oxides.
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