The Behavior of Nine Solar-Pond Candidate Salts

Purchasing and transporting salt are two of the most expensive items in the construction of salt-gradient solar ponds. The economics of solar ponds could be improved by using alternative salts that can be obtained free or at low cost. One such salt is sodium sulfate, which is expected to be widely available as a flue-gas desulfurization waste product. In this study, several highly soluble salts were tested for their suitability as solar pond materials in a laboratory salinity gradient pond. The salts tested were sodium chloride, sodium sulfate, sodium carbonate, sodium bicarbonate, magnesium chloride, calcium chloride, potassium chloride, potassium nitrate, and ammonium nitrate. Each of these salts has the potential to become a cheap, widely available resource. The behavior of the laboratory pond was monitored during testing of each alternative salt. Each salt's performance was compared with the performance of sodium chloride, the most commonly used salt in ponds. Predictions of stability were made and compared with experimentally derived stability as determined by the growth of convective layers. The investigators observed good agreement between experimental and theoretical ranking of the stability of each salt. However, it was apparent that more extensive Information on the properties of candidate salt solutions was needed.