Ancient China's coastal residents use seawater to make salt, introduce seawater into the salt field, use sunlight and wind to evaporate and concentrate seawater, so that it reaches saturation, and further make salt crystallization out. This method became evaporation crystallization in chemistry.
A.D. 1320 to A.D. 1378, in China's Jieshi Mountain north of the realm of the Lijin River along the coast of the Haifeng, Hairun, Haiying three salt farms. At the beginning of the Ming Dynasty, Hai Run, Hai Ying have frying and sun, Ming Shizong Jiajing first year (1522) Hai Feng field is the first easy to fry for the sun, has been used for more than two thousand years of the old traditional salt production process, was invented by the Wudi people instead of the new process, so that the salt industry has made a big step forward, the Wudi people of the contribution to the production of salt is not to be credited.
Sea water sun salt to strengthen the evaporation method is related to the liquid evaporation technology. Previously, seawater evaporation salt, are used plane evaporation method, brine and flowing water vapor unsaturated air contact area is limited to the plane area of the salt field, and strengthen the evaporation method to brine sprinkled at a certain altitude, or brine at a certain pressure and sprayed at a certain altitude, three-dimensional expansion of brine solution and flow of water vapor unsaturated air contact area, increase the area of evaporation, strengthen evaporation, and shorten the evaporation cycle and thus improve the brine production. Shorten the evaporation cycle to improve the evaporation efficiency of brine.
The chemical resource utilization of seawater is to evaporate and crystallize seawater first to precipitate bitter brine (containing magnesium ions, bromide ions, iodine ions, etc.) and crude salt (containing sodium ions, chloride ions, magnesium ions, sulfate ions, etc.). Then, add barium chloride, sodium hydroxide, sodium carbonate in turn. The impurities are removed, and the precipitate and filtrate can be obtained after filtration. After adding dilute hydrochloric acid solution, evaporation and crystallization are carried out, so that pure salt can be obtained.
Sea water is extremely rich in iodine, the total number is estimated to be 80 billion tons. Iodine is an important raw material on which national defense, industry, agriculture, medicine and other sectors and industries depend, and many countries in the world extract iodine from seawater.
The end of the 1970s, China put forward the concept of "ion *** valence", the successful study of JA-2-type adsorbent, iodine and bromine can be extracted directly from seawater; since then, the development of the liquid-solid distribution and other enrichment methods, iodine can also be extracted directly from seawater.
The brine after the sun salt can also produce iodine, of which, activated carbon adsorption method is relatively simple. Certain seaweed has the ability to adsorb iodine, such as dry kelp in the iodine content is generally 0.3% -0.5%, than the concentration of iodine in seawater 100,000 times higher. Therefore, the use of soaking liquid soaked kelp can also produce iodine.
China's sea salt production development is very fast, now 11 coastal provinces, autonomous regions and municipalities directly under the Central Government have salt fields, salt field area than the beginning of the country increased substantially. The quality of sea salt produced is also improving, and there are more and more varieties. In addition to the original salt, has been put into mass production of washing salt, crushed washing salt, refined salt, iodized salt, table salt, sausage salt, egg yolk salt and beach sun-dried fine salt, and in the trial production of flavored salt, salt bricks for feeding animals.
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