Question

Describe the preparation of potassium permanganate from pyrolusite ore.

Describe how potassium permanganate is made from pyrolusite. Write the chemical equations for the involved reactions.

Write the chemical equations involving the preparation of KMnO₄ from the mineral pyrolusite.

How is potassium permanganate manufactured from the mineral pyrolusite?

Answer 1

Potassium permanganate is manufactured from the mineral pyrolusite, MnO₂. The process involves the following two steps.

(i) Conversion of pyrolusite to potassium manganate: Pyrolusite ores are finely pulverized and fused with potassium hydroxide or carbonate in the presence of air or an oxidizing agent (e.g., potassium nitrate or potassium chlorate) to produce green potassium manganate.

\[\ce{2MnO2 + 4KOH + O2 ->[Heat] \underset{(green mass)}{\underset{Pot. manganate}{2K2MnO4}} + 2H2O}\]

\[\ce{2MnO2 + 4K2CO3 + O2 ->[Heat] \underset{(green mass)}{\underset{Pot. manganate}{2K2MnO4}} + 2CO2}\]

(ii) Oxidation of potassium manganate to potassium permanganate: After obtaining the fused mass, remove it with water until a green solution appears. This solution contains potassium manganate, which can be converted to potassium permanganate through two techniques.

(a) Chemical method: When potassium manganate is oxidized to potassium permanganate, it is treated with a current of carbon dioxide, chlorine, or ozone.

\[\ce{3K2MnO4 + 2CO2 -> 2KMnO4 + MnO2 + 2K2CO3}\]

\[\ce{2K2MnO4 + Cl2 -> 2KMnO4 + 2KCl}\]

\[\ce{2K2MnO4 + H2O + O3 -> 2KMnO4 + 2KOH + O2}\]

(b) Electrolytic method: This process uses iron electrodes to electrolytically oxidize potassium manganate. The potassium manganate solution is introduced into the electrolytic cell via an inlet iron pipe and a revolving wire-netting anode. The cathode is the iron pipe. The following reactions occur when an electric current passes.

At anode: \[\ce{\underset{(green)}{MnO^{2-}_4} -> \underset{(purple)}{MnO^-_4} + e-}\]

At cathode: \[\ce{2H+ + 2e- -> H2}\]

The purple solution from the preceding processes is evaporated under controlled conditions to get potassium permanganate crystals.

Laboratory preparation: In the lab, KMnO₄ can be produced by oxidizing a manganese (II) salt with peroxodisulphate.

\[\ce{2Mn^{2+} + 5S2O^{2-}_8 + 8H2O -> 2MnO^-_4 + 10SO^{2-}_4 + 16H+}\]