Question

Main impurities in bauxite are

• A. Fe\(_2\)O\(_3\), SiO\(_2\) and TiO\(_2\)
• B. CaO, MgO and SiO\(_2\)
• C. FeO, CaO and MgO
• D. CaSiO\(_3\), MgSiO\(_3\) and SiO\(_2\)

Hint:

To remember bauxite impurities, think of the "red mud" waste from alumina production. The red color comes from iron oxide (Fe\(_2\)O\(_3\)). The other two major components of this "mud" that came from the ore are silica and titania.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Bauxite is the primary ore for aluminum. It is not a pure mineral but a rock composed mainly of hydrated aluminum oxides (like gibbsite Al(OH)\(_3\), boehmite \(\gamma\)-AlO(OH), and diaspore \(\alpha\)-AlO(OH)). Along with these valuable minerals, bauxite contains several non-valuable oxide impurities, which must be removed during processing (via the Bayer process).

Step 2: Detailed Explanation:
The main impurities present in most commercial bauxite deposits are:

• Iron(III) Oxide (Fe\(_2\)O\(_3\)): Also known as hematite, this is usually the most abundant impurity and gives bauxite its characteristic red or brown color. During the Bayer process, it remains undissolved and is removed as the primary component of the "red mud" waste.

• Silicon Dioxide (SiO\(_2\)): Usually present in the form of kaolinite clay (Al\(_2\)Si\(_2\)O\(_5\)(OH)\(_4\)). Silica is a particularly troublesome impurity because it reacts with the caustic soda solution during digestion, leading to the loss of both valuable aluminum and expensive caustic soda.

• Titanium Dioxide (TiO\(_2\)): Also known as titania, this is another common impurity that is chemically inert in the Bayer process and reports to the red mud.
The combination in option (A) correctly lists these three main impurities. The other options include compounds like CaO and MgO, which are typically only minor impurities in bauxite.

Step 3: Final Answer:
The main impurities found in bauxite ore are iron oxide (Fe\(_2\)O\(_3\)), silica (SiO\(_2\)), and titania (TiO\(_2\)).