This separation process, which is carried out without salt solutions or a high consumption of energy, is based on a phenomenon that can also be observed in daily life. If two substances are rubbed together under certain physical conditions, they can attract contrary electric charges.
In principle, nothing different occurs in the ESTA plant (electrostatic separation), which was invented by K+S.
First of all the crude salt is fine milled to a grain size of one millimetre, so that the mineral conglomerate is broken down into its components. In the following step, the salts are treated with surface-active substances in a fluidised bed at a precisely defined temperature and humidity, so that electrons swap from one kind of mineral to the other.
Thus charged, the salt crystals trickle through a gravity separator, consisting primarily of two electrodes separated by a high-tension electric field. Negatively charged crystals are diverted in this field to the positive anode, and positively charged particles to the negative cathode. The sorted minerals are then caught separately below the gravity separator.