Crystallization solar salt

Naphthol Green B. A dye used in crystallizing solar salt, it increases the evaporation rate by added absorption of energy 5 ppm is said to increase salt production 15-20%. 

In warm countries sea water is concentrated in shallow flat basins by the sun, heat and wind until it crystallizes ( solar salt ). 

Similar to processing mined rock salt, solar salt may be cmshed, screened, and kiln dried or fluidized-bed dried. Coarse solar salt is a premium product because of high purity and relatively large crystal size. It is in particular demand for use to regenerate the resin in cation-exchange water softeners... 

Recovery Process. Figure 5 shows a typical scheme for processing sodium chlodde. There are two main processes. One is to flood solar ponds with brine and evaporate the water leaving sodium chlodde crystallized on the pond floor. The other is to artificially evaporate the brine in evaporative crystallizers. Industrial salt is made from solar ponds, whereas food-grade salt, prepared for human consumption, is mosdy produced in the crystallizers. 

FIGURE 6.1 Conditions used for evaporation for impurity removal, and the crystallization stage(s) for solar salt (sodium chloride) production from seawater. Operating details from Korovessis and Lekkas [II]. 

White Crystal. [Morton Salt] Variety of rode and solar salt grades. 

The products currently produced from sea water are listed in Table II. Solar salt (sea salt) is produced by evaporating sea water until the sodium chloride crystallizes. The resultant salt is separated from the bittern (primarily magnesium and potassium salts), washed with fresh water, and dried. Solar salt is used largely by the chemical industry in coastal areas, but in some parts of the world it is a source of salt for human consumption. 

Some potassium chemicals are currently separated from sea water by fractional crystallization of the bittern from solar salt production. Several years ago the Dutch operated a process which utilized dipicrylamine to precipitate potassium from sea water, but this reagent is rather costly. We are developing a... 

Example. Our reference plant, as shown by a later example in Section 7.1.7, requires a supply of about 1,300 tpd of salt. Operation for 350 days a year would consume 1300 X 350 = 455,000 tons annually. A solar salt plant operating for 200 days a year with an average evaporimeter rate of 10 nun per day requires a crystallizer area of about (0.9 X 455,(X)0)/(200 x 0.7 x 10) = 292 ha. The multipliers given in the text then suggest that the total area dedicated to supplying our plant must be 38 km. This is a rather good productivity. Bertram [2] notes that a 400,000 tpy plant can require 40 km or more. 

Open-pan solar evaporator. A very old but yet still used process is solar evaporation in open pans. Salt water is put in shallow open pans or troughs and allowed to evaporate slowly in the sun to crystallize the salt. 

Rock salt is obtained from mines and it is typically 95% sodium chloride. Alternatively, water is pumped into salt deposits to form brine underground. This brine is then removed through a brine well. After purification, the water is removed to make mechanically evaporated salt that is 99.99% sodium chloride. Controlled evaporation and fractional crystallization of seawater yields solar salt that is 99.7% sodium chloride. ... 

This leads to the replacement of the impure mother liquor by the wash solution, before the suspension becomes separated on the centrifuge. It has the advantage that the mother liquor in the crude crystallization, respectively the second crop, can be more concentrated that is, higher yields can be realized. Even solid impurities can be separated, if their settling rates are smaller than those of the product crystals. This is, for example, the case in the recrystallization of table salt from solar salt or in the case of the direct evaporative crystallization from solar pond concentrates, where... 

Recovery Process. The Texas Gulf, Cane Creek potash operation (60) of Moab, Utah produces KCl by solution mining (61—64). Brine is pumped from underground to 1.6 x 10 (400 acres) of solar ponds where a mixture of KCl and NaCl is crystallized in a salt mass called sylvinite. 

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