Production of salt from seawater involves the selective recovery of pure NaCl, free of other soluble or non-soluble salts and other substances. To this end, condensation of seawater by solar evaporation results in the fractional crystallization of all contained salts; a process based on their varying solubility in seawater.
Modern Solar Saltworks are multi-pond systems. They consist of a system of properly designed and constructed lakes (ponds) that are interconnected mainly in series. The seawater enters (by tidal action or pumping) the first lake in the row and appropriate control gates or pumps regulate its flow into the lakes system. The incident solar radiation, assisted by the wind action, evaporates the seawater and develops a salinity gradient in the lakes that results in salt crystallization in the latter lake in the row.
Thus, the pond system of Solar Saltworks consists of two main groups. The Evaporation Ponds, where the seawater is concentrated up to the saturation value with respect to NaCl and the Crystallizers where salt crystallizes and finally is collected.
The annual capacity of Solar Saltworks varies from some hundred to some million tons of salt, depending on the area used and the prevailing microclimate in the region. In seasonal Solar Saltworks the produced salt is harvested once every year and it is stored in open outdoor piles.