OCR Text |
Show 102 precipitate from the Lake during the winter. Brines can be stored during the winter in " cooling" ponds to precipitate the glauber salt, or artificial cooling may be used. Whether the glauber salt is dredged from the Lake bed, produced by refrigeration in a plant, or harvested from ponds, further necessary treatments may include crushing, washing, drying and dehydrating, and screening. These last processing steps are accomplished in the same manner as for sodium chloride except that higher temperatures may be required to accomplish drying and dehydration in the same step. Dehydration of glauber salt ( Na2SC> 4 • IOH2O) is necessary to produce salt cake or anhydrous sodium sulphate ( Na2S0^) for the major segment of the market. In 1939 and 1940, mirabilite was mined from the deposits described in " Geology and Geochemistry," then dissolved in a live steam, clarified, crystallized by evaporation, and dried, producing 99+ percent pure sodium sulphate. However, the fact that the deposits are small and that they are located along the south shore, a natural recreation site, indicates that exploitation of these deposits would probably be unwise. Another of the first minerals to precipitate from the Lake by solar evaporation is astrakanite, which contains both sodium sulphate and magnesium sulphate. Because magnesium sulphate is more soluble than sodium sulphate, mixing or leaching astrakanite with a limited amount of water causes the magnesium sulphate to be dissolved along with part of the sodium sulphate. The remaining solid sodium sulphate can then be filtered or centrifuged from the leach solution, washed, dried, dehydrated if necessary, and screened. The amount of water of hydration accompanying the solid sodium sulphate depends upon the leaching temperature. |