Salt is a condiment commonly eaten by human beings and an indispensable substance for human body. According to the statistics of scientists, a healthy adult should absorb 5 ~ 2g of salt from various diets every day. These salts can maintain the osmotic pressure of human blood, promote blood circulation and maintain the normal metabolism.
Salt is also a basic raw material for chemical industry. Sea salt is used as raw material to make soap, refine petroleum, steel and aluminum, refine soda ash and caustic soda, and produce hydrochloric acid and chemical fertilizer ammonium chloride. It can be said that in the chemical industry, most products that use sodium and chlorine are derived from sea salt. Therefore, salt is not only a necessity of human life, but also the mother of chemical industry.
China has a long coastline and many beaches along the coast. The flat, vast, sunny and dry weather has extremely favorable conditions for the development of sea salt production. Therefore, the output of sea salt ranks first in the world, and it has been used to make salt for thousands of years.
boiling the sea for salt and drying in the beach are two major methods to extract salt from seawater.
To cook the sea for salt is to take the sea water ashore, put it in an iron pan and other equipment, and burn it with fire. When the sea water boils, it will evaporate water vapor, so that the sea water will be concentrated into bitter brine, and then the bitter brine will continue to evaporate. At last, the salt will become crystals like rock sugar and run out of the sea water. It is recognized by world historians that China was the first country to extract salt from seawater. According to the research of cultural relics, as early as 5 years ago, our ancestors had boiled salt with seawater. According to legend, there was a Fengsha family in history. He was a contemporary of Shennong, who first cooked the sea for salt.
another method of making salt from seawater is the beach drying method. The place where the salt is dried on the beach is Yantian, which is generally built on the beach. With the rising slope of the beach, a first-class pool like an escalator is opened, and seawater is pumped into the pool by high tide, windmill or pump. Seawater flows through several ponds. With the wind and the sun, the water evaporates continuously, and the salt concentration in seawater becomes higher and higher. Finally, concentrated salt enters the crystallization pond and continues to evaporate until salt crystals are separated.
In China, the beach drying method first appeared in the Yuan Dynasty, and in the Kangxi period of the Qing Dynasty, the Changlu salt area in North China was opened on a large scale, and salt was dried on a large scale. The methods of making salt from seawater in other countries are basically similar to those in China. Interestingly, when the United States realized the patent law, the first patent was the technology of drying salt on the beach, which is economical and effective and is still widely used in modern times.
At present, there are more than 4, salt-making workers in China. With modern mechanical operation and scientific management, the production of sea salt is increasing year by year, and it can produce nearly 2 million tons of sea salt every year, accounting for 8% of the total salt production, ranking first in the world.
in the method of making salt, there is also a freezing method. In countries such as Sweden and the former Soviet Union, they let the sea water naturally cool into ice, which is almost composed of fresh water, and the rest is bitter brine, that is, strong brine. After freezing bittern several times, the brine is getting thicker and thicker. Finally, salt crystals are obtained by artificial heating. This method can only be produced in winter and its yield is not high.