CDS (I) 2021 General Knowledge · Question 23 of 120

Correct — B, Bauxite ore. The school text puts it exactly: though several ores contain aluminium, it is from bauxite, a clay-like substance, that alumina and later aluminium is obtained. Bauxite forms by the decomposition of a wide variety of rocks rich in aluminium silicates, under hot wet conditions that leach the silica away and leave hydrated aluminium oxides behind. Production runs in two stages — bauxite is first refined into alumina, and alumina is then reduced to the metal in an electrolytic cell, which is why aluminium smelters are built next to cheap power rather than next to mines. The metal is worth this trouble because it combines the strength of metals such as iron with extreme lightness, along with good conductivity and great malleability. In India, Odisha leads production, and the Panchpatmali deposits in Koraput district are the most important in that state.

• (a)Copper ore — Yields copper, not aluminium, and India's output is small relative to demand. The leading producers are the Balaghat mines in Madhya Pradesh, the Khetri mines in Rajasthan and the Singhbhum district of Jharkhand.
• (c)Mica ore — Mica is not worked as a metal ore at all. It is a sheet silicate valued for splitting into thin transparent sheets with excellent dielectric strength and heat resistance, which is why it goes into electrical and electronic equipment.
• (d)Manganese ore — Manganese is a steel-making and battery mineral. Its principal use is in the manufacture of steel and ferro-manganese alloys, and it also goes into dry batteries — a different metal for a different purpose.

An ore is a mineral accumulation from which a metal can be won at a profit, so a metal's ore is decided by chemistry and economics together. Aluminium is the most abundant metal in the earth's crust but is locked into silicates that are far too costly to break down, and bauxite is the one common deposit in which it occurs as hydrated oxides that can be handled economically. The metal's own history follows its electricity supply: it was a laboratory curiosity until electrolytic reduction was developed in the 1880s, and it remains among the most power-hungry metals to produce.

A single-line ore-to-metal question is decided by knowing the pairs, and the four options here are the four minerals a candidate is most likely to have met in the same chapter. Building the list in both directions helps — bauxite gives aluminium, haematite and magnetite give iron, chalcopyrite-bearing ores give copper, pyrolusite gives manganese, and mica gives no metal at all. Two further points recur in question papers: aluminium smelting is located by power supply rather than by the mine, and India's bauxite and its aluminium plants are largely in the eastern belt across Odisha, Jharkhand and Chhattisgarh.

• Aluminium is obtained from bauxite, which is first refined into alumina and then reduced electrolytically to the metal.
• Bauxite deposits form by the decomposition of rocks rich in aluminium silicates.
• Aluminium is valued because it combines the strength of metals such as iron with lightness, good conductivity and great malleability.
• Odisha was India's largest bauxite-producing state in 2018-19, with the Panchpatmali deposits of Koraput district the most important.
• Copper in India comes chiefly from Balaghat in Madhya Pradesh, Khetri in Rajasthan and Singhbhum in Jharkhand.
• Manganese is used mainly in steel and ferro-manganese alloys and in dry batteries; mica is an insulating sheet silicate, not a metal ore.

• Treating mica as an ore of a metal; it is an insulating mineral.
• Assuming a metal's ore must be where the metal is most abundant; aluminium is abundant in silicates that cannot be worked economically.
• Confusing bauxite mining regions with alumina refining and smelting locations, which follow electricity.

As a direct ore-to-metal question, or as a match-the-following pairing minerals with their uses or their mining districts.

• practice — not a real PYQ

  Aluminium smelters are usually located near sources of cheap electricity rather than near bauxite mines because

  • (a)bauxite cannot be transported by rail
  • (b)the reduction of alumina to aluminium consumes very large amounts of electricity
  • (c)aluminium loses strength if it is produced close to a mine
  • (d)alumina is produced only in coastal states

  Answer(b) the reduction of alumina to aluminium consumes very large amounts of electricity — the electrolytic stage, not the mining, dominates the cost.

• practice — not a real PYQ

  Which one of the following minerals is used mainly in the manufacture of steel and ferro alloys and in dry batteries?

  • (a)Bauxite
  • (b)Mica
  • (c)Manganese
  • (d)Limestone

  Answer(c) manganese — its dominant use is in steel and ferro-manganese, with dry batteries a secondary outlet.