Muriate and Sulphate of Potash | Potash Fertilizers

After reading this article you will learn about the manufacture and use of muriate and sulphate of potash.

Manufacture of Muriate and Sulphate of Potash:

Potash fertilizers include Muriate of potash and sulphate of potash, which are manufactured from the following minerals:

(i) Sylvinite or sylvite KCl – It contains 63.1% K₂O

(ii) Carnalite KCl MgCl₂6H₂O – It contains 17.1% K₂O

(iii) Kainite KCl MgSO₄3H₂O – It contains 18.9% K₂O

(iv) Langbeinite K₂SO₄MgSO₄ – It contains 26.6% K₂O

Muriatic acid and muriates are the old names of hydrochloric acid and its salts respectively.

Manufacture of Muriate of Potash:

Sylvinite or Sulvite is dissolved in hot water and sodium chloride is added to it. The temperature of the solution is gradually increased and more sylvinite is gradually added to it, until a hot saturated solution of potassium chloride is formed. This is suddenly cooled and crystals of potassium chloride separate, which are removed, dried and bagged.

Manufacture of Sulphate of Potash:

Langbeinite is dissolved in hot water to which magnesium sulphate is also added. The temperature of the solution is gradually increased and more Langbeinite is dissolved until a saturated solution is formed.

When it is suddenly cooled crystals of magnesium sulphate separate, because these are less soluble than potassium sulphate. These are removed by filtration. When the mother liquor is evaporated, crystals of potassium sulphate separate.

These are dried and bagged. Muriate of Potash is a reddish or dirty white crystalline material which contains about 61 per cent K₂O.

Sulphate of Potash is a dirty white powder which contains about 52 per cent K₂O.

Reaction of Soil:

When potassium chloride and potassium sulphate are added to the soil, they are assimilated by plants.

Potassium ions replace other ions from the clay and humic micelle as shown below:

Some potassium ions are also fixed by clay minerals like illite and vermiculite.

Use of Muriate of Potash and Sulphate of Potash:

Muriate of potash should be added to acidic and clayey soils. Sulphate of potash should be added to sandy to loamy soil and paddy fields, alkaline and calcareous soils and highly leached acidic soils which are deficient in sulphur.

Sulphate of potash is more expensive than Muriate of potash thus sulphate of potash should be applied to the vegetable and fruit to improve their quality.

Other Sources of Potash:

Other sources of potash include wood ash, tobacco stem and water hyacinth. Wood ash contains about 5-6 per cent potash in the form of potassium carbonate, 1-2 per cent phosphorus (P₂O₅) and 25-30 per cent lime. Wood ash therefore may be used to neutralize soil acidity. Finely ground tobacco stem contains 2-3 per cent of nitrogen, 6-10 per cent of readily available potash.

Dry water hyacinth contains about 1 per cent N, 4 per cent K and a small quantity of phosphorus. The ash of paddy husk, sugarcane bagasse and groundnut shell also contains a fair amount of potash and some phosphorus.