Evaporated salt

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. 

Salt produced in the United States varies in purity from 95% NaCl for rock salt to 99.99% NaCl for mechanically evaporated salt. Mechanically evaporated salt made using purified brine generally has the highest purity rock salt generally has the lowest. Several voluntary standards and mandatory specifications apply to salt to ensure appropriate gradation, quaUty, and purity for particular salt uses (Table 4). 

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. 

Evans diagram, 7 802-804 Evaporated salt, in water softening,... 

The chlorine-free brine, still as a weak solution, can then be recirculated to the resaturator. Care should be taken in partial or staged conversions not to feed any diaphragm cell evaporated salt to membrane electrolysers as it may contain chromium and nickel from the evaporators, which are harmful to the membrane. 

Not all diaphragm plants would consider conversion. In the case of plants where the diaphragm caustic soda from the cells is fed to a downstream plant there is no economic driver to convert. Indeed, ICI Chlor-Chemicals has a diaphragm plant where the sole requirement is the use of the diaphragm cell caustic as a reagent for treating raw brine for multiple chlor-alkali plants, ammonia soda plants and evaporated salt plants. 

Salt is very widely diffused in the waters of the globe. Most rivers carry traces, and when they discharge into land-locked basins, and when the waters are cone, by evaporation, salt-lakes are formed. The waters of the Baltic Sea contain between 02 and 08 per cent, of saline matters, whereas the waters of the Dead Sea contain up to 25 per cent. It has been estimated that next to water, salt is one of the most abundant mineral substances on the crust of the earth. The composition of the solids held in soln. in the waters of a number of oceans and seas is indicated in Table XIV. 

DISSOLVE 19 g TABLE SA LT (NoCI) IN 50 ml HOT WATER. BOIL SOLUTION, STIRRING WITH GLASS TUBE WITH TOP END SEALED (TO REDUCE "BUMPING"), UNTIL HALF THE WATER HAS BEEN EVAPORATED. SALT FORMS FINE CRYSTALS. 

There is a possibility that the advantages of salt as a dispersing agent could be utilized, without the disadvantages of the pressed-salt method, by using high-area evaporated salt. This type of salt was used as an adsorbent by deBoer (61) in his studies of the color and ultraviolet spectra of adsorbed dyes. 

Key environmental disadvantages regarding the use of evaporation technology in this application were identified, included disposal of the salt cake and substantially increased electrical consumption. With respect to disposal of the evaporated salts, the crystals formed would be readily soluble in water, and as a result, dissolve in any... 

Evaporated salt is of sufficient purity that it is used as a food ingredient for humans and animals, as well as a raw material for chemical reactions and polishing pharmaceutical tablets. Purified salt can also be used in food processing, and is frequently used in the pharmaceutical industry to make hemodialysis and intravenous fluids.6... 

Calcium and Magnesium Salt Other than Evaporated Salt with Only Anticaking Agents Such as Sodium Ferrocyanide Not more than 0.9% Evaporated Salt with Only Anticaking Agents Such as Sodium Ferrocyanide Not more than 0.35%. Heavy Metals (as Pb) Not more than 2 mg/kg. 

Sample Preparation for Evaporated Salt Transfer 10.0 g of sample into a 400-mL beaker, and dissolve in 100 mL of water. If free-flowing agents are present, filter and rinse quantitatively. Dilute the solution or filtrate to 200 mL with water. 

Solid state reactant Thermal decompositions of a solid Oxidation or reduction of a solid Precipitation Solution heating or cooling Evaporative salting-out Chemical reaction with insoluble product Hydrothermal synthesis Forced insolubility Dissolution reprecipitation Evaporative Condensation Gas phase reaction with solid product Thermal decompositions Oxidation or reduction reactions Combination reactions with a solid product Solvent removal Spray drying Freeze drying Spray roasting Sol-gel synthesis Melt solidification... 

Black shales, phosphatic sediments. Sometimes enriched in soluble evaporative salts formed in evaporative lake sediments, and in agricultural soils developed from Se-rich rocks. Smelter particulates and smelter-affected soils. Some rock and sediment types, as well as their derived soils, are naturally depleted in Se, for example some dust-derived sediments (loess), some granites or gneissic metamorphic rocks. 

The Owens Lake dusts are derived from lake bed sediments containing abundant alkaline evaporative salts of sodium, chloride, carbonate/ bicarbonate, and sulfate, including, e.g., halite, natron, thermonatrite, mirabilitie, and trona (Saint Amand et al, 1986). In addition, the dusts contain a variety of silicates and other minerals derived from local alluvial material, and possibly some mine waste materials from the Cerro Gordo lead-zinc-silver mining district on the east end of Owens Lake. 

Salinization of soil results from a combination of evaporation, salt precipitation and dissolution, salt transport, and ion exchange (Shimojima et al., 1996). Excessive salinity in soil leads to toxicity in crops, reduction in soil fertility, reduction of... 

Evaporated salt can be obtained by evaporating brine. Pretreatment of the brine is necessary to attain sufficient purity. Calcium, magnesium and sulfate ions, in particular, have to be removed ... 

The evaporation is carried out in multistage plants. Evaporated salt is very pure (> 99.95%, with ca. 100 ppm ofCa2+). 

Utilization of evaporated salt is gaining in importance due to the progressive introduction of chloralkali membrane electrolysis technology, which places high demands on the purity of the sodium chlorine-brine utilized. 

Purification of the brine by precipitation of impuritie.s in the production of evaporated salt... 

Depending upon the electrolysis process utilized amalgam, diaphragm or membrane, different additional purification steps are required. In the mercury process, solid salt is utilized, which is dis.solved in water. If evaporated salt is used, purification can be carried out in a small branch loop. When mined salt is utilized, care has to be taken during dissolution to settle out the impurities. Soluble impurities are removed by precipitating S04 with Ba +, precipitating Mg + and Fe- as hydroxides by the addition of NaOH and precipitating Ca as carbonate with sodium carbonate (see the production of evaporated salt). 

Sodium is the most abundant metal in sea water. Sodium chloride is commercially produced from sea water by solar evaporation. Salt is a dietary necessity, but only a small fraction of the production is actually used as table salt in foods. The chemical usages for sodium are so extensive that salt is one of the most important raw materials for the chemical industries. 

These features are likely to encourage further development of vacuum or solar evaporation salt recovery operations to work these brines in proximity to the desalination plants. In this way, various salts may be more profitably recovered from these artificially enriched seawaters for reasons similar to the present incentives to use the rich natural brine sources for sodium chloride production (Table 6.3). Similar energy savings should be obtained. 

Natural brines produced from shallow wells in the Kiser and Chaney salt plains are saturated with respect to salt (Table I). (Na + Cl) comprise 327 and 335 g/1 of brine samples, and they represent more than 99% of the dissolved solids in the brine. Two companies have produced solar-evaporated salt from these brines. The brines are pumped at rates of 300—400 l/min. from wells drilled 9—12 m deep into natural cavities in salt layers (Johnson and Denison, 1973). 

The conditions necessary for artificial synthesis of smectites suggest the kind of natural environment in which these minerals will be found. This environment is alkaline as a result of restricted drainage and/or evaporative salt accumulation (see Chapter 8), so that the normally mobile alkaline and alkaline earth ions (Na, K, Ca, Mg) accumulate, along with silica. Neoformation of smectites from Na-rich saline water, and possibly illites from more K-rich water, is favored under these conditions. Other very silica-rich silicate minerals, such as attapulgites, sepiolites, and zeolites, are also known to fomi under these conditions. Less alkaline conditions may be necessary for Fe and Al-rich (dioctahedral) smectite formation, and a reducing environment may assist crystallization. 

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