Hot dissolution process
The hot dissolution process is based on dissolution behaviour dependent on different temperatures. While rock salt dissolves in water equally well irrespective of its temperature, the solubility of potassium chloride increases, as the temperature rises.
For instance, while a litre of water at 25º C can only take up 137 grams of potassium chloride, it will already take up 265 grams per litre at 95º C.
In order to separate the potash from the crude salt, a salt solution saturated with rock and potash salt is heated. Following heating, the solution continues to be saturated with rock salt, while the amount of potash that can be dissolved increases as the temperature rises.
Crude salt is now added to the hot solution. The potash minerals are dissolved and the rock salt remains undissolved as a solid. The solid rock salt is then separated out by being filtered or centrifuged and settled. Potassium chloride with a purity of up to 97 percent is then won from the hot clear solution by being cooled in vacuum crystallisation units.