Solar salt

Principles. Solar salt results from natural evaporation of seawater or brine in large ponds. Its production is a slow process. The retention time from intake of seawater to harvesting of salt is usually several years. Even brine from wells, which is much more concentrated to begin with, requires a year or more. Because the rate of evaporation and the success of salt production depend on local weather patterns, it is an uncertain business and one that must follow a yearly cycle. Many solar salt plants make product during only part of the year. 

Because of the complex constitution of seawater, many species other than NaCl can precipitate from solution. Therefore, the production of solar salt involves a sequence of 

The first salt produced by solar evaporation, many centuries ago, would have had approximately the composition tabulated above. Its taste would have been very bitter. Technology began to advance when someone noticed that the taste deteriorated rapidly toward the end of the evaporation. By draining off the last small volume of brine and harvesting the salt already formed, the solution responsible for the bitterness, still referred to as bitterns, was isolated. Similarly, someone noticed at some point that the first material precipitated was not salt. By making a cut on the front end, transferring the brine after the onset of NaCl precipitation to another pond, the amount of gypsum in the product was also reduced. This simple technique is the essence of the methods used today. 

Baseggio evaporated the seawater and reported its composition as a function of density, noting the onsets of gypsum and salt crystallization. The water used was about 10% more concentrated than water from the open oceans (3.76% total salts vs 3.42%) but was identical in salt composition. Evaporation continued until the density of the remaining brine reached 1.25, just at the onset of magnesium precipitation. The volume by then had been reduced to about 3.5% of its starting value salt precipitation did not begin until the volume was reduced by about 89%. 

The curves of Fig. 7.3 qualitatively show the course of precipitation of the solids. From the onset of NaCl crystallization until the final density is reached, about 77% of the salt precipitated in Baseggio s work, the rest remaining with the bitterns. The CaS04 crystallizing along with the salt represents a dry-basis concentration of 0.6%. This can 

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Solar evaporation Solarization Solar panels Solar ponds Solar power systems Solar radiation 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... 

Electrodialysis. Electro dialytic membrane process technology is used extensively in Japan to produce granulated—evaporated salt. Filtered seawater is concentrated by membrane electro dialysis and evaporated in multiple-effect evaporators. Seawater can be concentrated to a product brine concentration of 200 g/L at a power consumption of 150 kWh/1 of NaCl (8). Improvements in membrane technology have reduced the power consumption and energy costs so that a high value-added product such as table salt can be produced economically by electro dialysis. However, industrial-grade salt produced in this manner caimot compete economically with the large quantities of low cost solar salt imported into Japan from Austraha and Mexico. 

Highway. Rock salt, solar salt, and in some cases in Europe, evaporated salt are used to maintain traffic safety and mobiUty during snow and ice conditions in snowbelt regions throughout the world. Sodium chloride melts ice at temperatures down to its eutectic point of —21.12°C. Most snowstorms occur when the temperature is near 0°C, where salt is very effective. More than 40% of dry salt produced in the United States is used for highway deicing. 

V. M. G. Mannar and H. L. Bradley, Guidelines for the Establishment on Solar Salt Facilities from Seawater, Underground Brines and Salted Takes, United Nations Industrial Development Organi2ation, 1983. 

Sodium nitrate is also used in formulations of heat-transfer salts for he at-treatment baths for alloys and metals, mbber vulcanization, and petrochemical industries. A mixture of sodium nitrate and potassium nitrate is used to capture solar energy (qv) to transform it into electrical energy. The potential of sodium nitrate in the field of solar salts depends on the commercial development of this process. Other uses of sodium nitrate include water (qv) treatment, ice melting, adhesives (qv), cleaning compounds, pyrotechnics, curing bacons and meats (see Food additives), organics nitration, certain types of pharmaceutical production, refining of some alloys, recovery of lead, and production of uranium. 

Solar salt operations can be found along the shores of the Great Salt Lake and in the San Francisco Bay area (6—10). Salt production from these areas represents 10% of the total salt produced in the United States. 

Total solar salt, NaCl, produced in the world is 90 million tons. Well over that amount of salt is produced in preconcentration ponds as an intermediate step in the production of other chemicals such as potassium chloride. For example, the Dead Sea faciUties produce 40 million tons of salt each year but sell none because of the high cost of transportation to markets. 

Where possible, solar salt is replacing vacuum salt because of rising energy costs. For example, in July the 81 x 10 (20,000 acres) of solar ponds... 

There has been much interest in making chemicals from brine because of the low expense compared to alternative methods. Lithium, for example, had been mostly produced from spodumene ore, but now most is produced from brine. Those now producing from ore are seriously researching brine reserves and contemplating converting to brine sources before the turn of the century. Similady, solar salt has cost advantages over mined rock salt. Potassium chloride produced from brine has more than doubled from 1980 to 1990. 

Brine Preparation. Rock salt and solar salt (see Chemicals frombrine) can be used for preparing sodium chloride solution for electrolysis. These salts contain Ca, Mg, and other impurities that must be removed prior to electrolysis. Otherwise these impurities are deposited on electrodes and increase the energy requirements. The raw brine can be treated by addition of sodium carbonate and hydroxide to reduce calcium and magnesium levels to below 10 ppm. If further reduction in hardness is required, an ion-exchange resin can be used. A typical brine specification for the Huron chlorate ceU design is given in Table 6. 

Solar-grade silicon, production of, 22 507-508 Solar heat control, use of gold in, 12 703 Solarization effect, 19 203 Solar photocatalysis, 23 23-24 Solar photocatalytic detoxification, 19 76 Solar photocatalytic processes, 19 100-101 Solar photocatalytic reactor, using deposited titania, 19 99 Solar photoreactors, 19 95-99 Solar salt harvesting, 22 802, 806-808 Solar spectrum, 23 2 Solar still, 26 89-92 Solar thermal converters, 23 10-13 Solar transmittance, for thin films, 23 19 Solatene, 24 558 Solder, 3 53... 

PVA in, 25 615-617 Wash brine, in solar salt harvesting, 22 807-808 Washcoat, 10 103... 

E.-F. GeofEroy stated that sal ammoniac, because of its volatility and die manner in which it used to be prepared, was often called the heavenly eagle, the flying lUtle bird, die solar salt, or die mercurial soot (43). Herman Boerhaave believed diat, since Vesuvius and other volcanoes eject sal ammoniac, it is therefore necessary to class this salt with die fossils, although it is believed that that which is now being brought to us is an animal production (75). By die word fossil Boerhaave and his contemporaries meant a mineral, or substance dug from the earth. 

Solar salt - [CHEMICALS FROMBRINE] (Vol 5) - [SODIUMCOMPOUNDS - SODIUT TALIDES - SODIUMCITLORIDE] (Vol 22) -chlorates from [CPHORINE OXYGEN ACIDS AND SALTS - CPHORIC ACID AND CITLORATES] (Vol 5)... 

Saltmarsh and the San Diego Bay Solar Salt Pond, Both Sites are Near San Diego, CA. 

Sample Preparation for Rock and Solar Salts Transfer 50.0 g of sample into a 500-mL volumetric flask, dissolve in 400 mL of water containing 2 mL of hydrochloric acid, dilute to volume with water, and mix. Filter a 50-mL aliquot, then pipet 10.0 mL of the filtrate into a 400-mL beaker, and add 190 mL of water. 

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