Manufacture of KMnO4 from Pyrolusite Ore

Preparation of Potassium Permanganate from Pyrolusite

Potassium permanganate is manufactured commercially from the ore pyrolusite (MnO₂) by fusing the powdered ore with potassium hydroxide (KOH) and an oxidizing agent like air to form potassium manganate (K₂MnO₄), followed by either chemical oxidation of the manganate with chlorine or electrolytic oxidation to yield potassium permanganate (KMnO₄).

Overall Process: MnO₂ → K₂MnO₄ → KMnO₄

Stepwise Manufacturing Process:

A. Finely powdered pyrolusite ore (MnO₂) is mixed with potassium hydroxide (KOH).
B. Mixture is heated in the presence of an oxidizing agent, such as air, KNO₃, or KClO₃ produce dark green potassium manganate (K₂MnO₄).

2MnO₂ + 4KOH + O₂ → 2K₂MnO₄ + 2H₂O

Oxidation of Potassium Manganate to Potassium Permanganate:

It can be done by two process:

1. Chemical Oxidation
2. Electrolytic Oxidation

Chemical Oxidation:

An oxidizing agent is used to convert the manganate ions to permanganate ions.

Oxidation by Chlorine
2K₂MnO₄ + Cl₂ → 2KMnO₄ + 2KCl

Oxidation by Ozone
2K₂MnO₄ + O₃ + H₂O → 2KMnO₄ + 2KOH + O₂

Electrolytic Oxidation:

This is the most common and efficient method used industrially as it produces high-purity potassium permanganate. An electric current is passed through a solution of potassium manganate. The reaction occurs at the anode, where manganate ions are oxidized to permanganate ions by losing an electron.

2K₂MnO₄ → 2K⁺ + MnO₄^2–
H₂O → H⁺ + OH^–

At anode, manganate ions are oxidized to permanganate ions.
MnO₄^2– → MnO₄^– + e^–

Also read Class 12 d-Block Elements