Solar evaporation process

Solar evaporation process for obtaining sodium chloride. 

Investigation of the Isothermal and Solar Evaporation Processes of the Effluent from the Iodine-Bromine Plant... 

Another mining process involves the recovery of sodium carbonate decahydrate from alkaline ponds. EMC mines this material from its solar evaporation pond using a bucket wheel dredge. The decahydrate slurry is dewatered, melted, and processed to soda ash. 

SQM Nitratos (Chile) operates two sodium nitrate plants in northern Chile Pedro de Valdivia and Mama Elena, about 30 km distant from one another. The caUche is mined in open-pit areas. A solar evaporation plant, Coya Sur, Hes in between. A flow sheet of the processing operations for sodium nitrate production is shown in Figure 2. 

At Great Salt Lake Minerals Corporation (Utah), solar-evaporated brines are winter-chilled to —3° C in solar ponds. At this low temperature, a relatively pure Glauber s salt precipitates. Ponds are drained and the salt is loaded into tmcks and hauled to a processing plant. At the plant, Glauber s salt is dissolved in hot water. The resulting Hquor is filtered to remove insolubles. The filtrate is then combined with soHd-phase sodium chloride, which precipitates anhydrous sodium sulfate of 99.5—99.7% purity. Great Salt Lake Minerals Corporation discontinued sodium sulfate production in 1993 when it transferred production and sales to North American Chemical Corporation (Trona, California). 

Magnesium chloride can be also recovered from its mineral carnallite by similar processes involving concentration of the liquor by solar evaporation followed by separation of other salts by fractional crystallization. 

Potassium chloride is produced by several processes. The salt is recovered from natural brine by solar evaporation in shallow ponds. Various methods are employed in mining ores from their natural deposits. Usually it is recovered from sylvinite or a naturally occuring complex mixture of langbeinite and kainite. 

The three main industrial methods used to produce salt are the solar evaporation method, mining of rock salt, and solution mining. The solar evaporation method is the oldest process used to obtain salt. This method is applied in geographic areas with high solar input and low... 

Countries not favoured with rock-salt must either import salt from more favoured countries, or resort to the cone, of sea-water, or of the brine from salt-springs, etc. Evaporation is not an expensive process in warm countries, or where coal is cheap. The brine is cone, by solar evaporation, in large hollow tanks or ponds exposed to wind and sun, on the shores of the Mediterranean and the Black Seas on the tide-lands around San Francisco Bay and on the banks of the brine-lakes of the United States. According to C. Ochi,5 10,000 tons of salt are annually extracted from the sea-water at Kaoo-Chew Bay (China). 

Sea water is an inexhaustible source of salt one litre contains on the average 35 g of various salts of which approximately 27 g is sodium chloride. Sea water salt is obtained primarily in countries with a hot, dry climate and is a result of solar evaporation in the so called salt fields, i. e. on the coast of France, Italy, Dalmatia, Spain, Portugal, USA and Japan. A less common method of sea water processing is artificial evaporation as in Normandy or winterization as in the USA. 

Brines containing 33-34% MgCl2 may be derived as a by-product from the potassium industry or produced by dissolving magnesium-bearing minerals in hydrochloric acid. Naturally occurring dilute brines are concentrated by solar evaporation or conventional dehydration processes. To avoid hydrolysis above 200°C, the final dehydration is performed in an atmosphere of hydrogen chloride. 

Sulfate of potash (K2S04), unlike the earlier-discussed potash salts, does not occur as natural deposits. It can be recovered by fractional crystallization from such natural brines as those of the Great Salt Lake in Utah and Searles Lake in California. Here separation and recovery are achieved by solar evaporation in shallow ponds. These processes can be utilized only where a suitable brine source is available, and where solar evaporation rates are high. 

The evaporation process can be divided into the broad categories of steam evaporation and solar evaporation. 

Aside from the solar evaporation method, precipitation 22 25), electrolytic 26 3l), and ion exchange 32,33> processes have been tested for sodium recovery, but only on a small scale in contrast, electrodialysis has been more significant. 

Solar evaporation, from primary and secondary ponds of 100 and 30 km in extent, the initial stage for potassium chloride recovery from the Dead Sea brines [26]. The smaller number of constituent ions present in these waters significantly simplifies salts recovery, and the fact that they contain nearly twice the relative potassium chloride concentration of seawater also improves profitability. Developed from a process, which was first operated in 1931, evaporation in the first pond reduces the volume of the brine to about one-half of the initial volume and brings down much of the sodium chloride together with a small amount of calcium sulfate (Fig. 6.5). The concentrated brines are then transferred to the secondary pond where evaporation of a further 20% of the water causes carnallite (KCl MgCli 6H2O) and some further sodium chloride to crystallize out. With care, a 95% potassium chloride product on a scale of some 910,000 tonne/year is obtained either by countercurrent extraction of the carnallite with brines, or by hot extraction of potassium chloride from the sylvinite matrix followed by fractional crystallization for its eventual recovery [16]. 

Processes, which recover sodium or potassium chlorides from natural brines originating from the ocean or salt lakes probably, have the least salination impact on surrounding lands. Since many of these operations use solar evaporation, they also have a low external energy requirement. The ratio of reserves to annual production rates, even for the salt lakes, is so large that there is not likely to be any noticeable salinity decrease for many years. 

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