How to Utilize Concentrated water after Seawater desalination

Due to the increasing demand for fresh water, the use of seawater desalination machine is increasing, and the high-salinity concentrated water produced by desalination, especially containing pretreatment chemicals, will cause damage to the environment if it is discharged improperly.

Salt (sodium chloride), magnesium, potassium, and bromine are the main elements of high-salinity concentrated water, and they are also the basic raw materials of the chemical industry. Therefore, so large amounts of concentrated water is also waste of resources.

Since the concentration of chemical substances in the concentrated water after seawater desalination is approximately doubled, it is can help reduce the energy consumption of extracting chemical substances and will be easy to realize process co-production to reduce water production cost of seawater desalination.

Therefore, the resource utilization of concentrated seawater can not only solve the impact of its discharge on the environments, but also turn chemical substances into treasure, thereby improving the efficiency of seawater desalination.

1. Marine salt production

Salt is the most basic chemical raw material, and it is also necessity in people daily life. There are mainly two commonly used marine salt production technologies, namely the salt field method and the electrodialysis method.

The salt field method is an ancient method of salt production, and it is also a method that is still commonly used in China. The process of salt production includes steps such as moisture absorption, brine production, crystallization, salt mining, storage and transportation. my country has a long history of sea salt production from salt fields.

Electrodialysis is a new method of salt production with the development of membrane separation technology. The method uses selective ion exchange membrane electrodialysis to concentrate halogen production and vacuum evaporation to produce salt. It can make full use of the large amount of concentrated seawater with high salt content produced by desalination as raw materials to produce salt. Compared with the salt field method, the electrodialysis method saves a lot of space and human cost, also be not affected by the season.

2. Extract potassium from seawater

Potassium is one of the three major elements of plant growth. According to statistics, the world's average total consumption of potash fertilizer is 60 million tons per year. However, due to the uneven distribution of terrestrial potash, 90% of the global terrestrial soluble potash ore storage and production are concentrated in 7 countries. Thus most countries are poor in potash mines and rely on imports.

Since the Norwegian scientist Jilland proposed the first patent for extracting potassium from seawater in 1940, there have been more than 100 patented methods including chemical precipitation. Both the seawater extraction method of potassium and the industrialization pilot test have achieved stage success. However, due to the complex composition and thin concentration of seawater, the technology for efficient separation and extraction of potassium salt is difficult, especially because the cost is extremely high,  industrialization has not been achieved.

3. In addition, there are seawater extraction of bromine (mainly by the air blowing method developed by the American DOW Chemical Company), seawater production of magnesium (mainly precipitation method), seawater extraction of lithium and seawater extraction of uranium (mainly by adsorbent method).

According to the current desalination process, each cubic meter of fresh water produced will produce 1.0 to 2.0 cubic meters of concentrated water. If 80% of the concentrated water is used, the industrial chain of about 1.2 million tons of potash fertilizer, 120,000 tons of bromine, 2.5 million tons of magnesium salt materials and 15 million tons of refined salt can be formed. Therefore, seawater desalination system, especially the utilization of concentrated water resources, not only can obtain good comprehensive economic benefits, but also has a very broad prospect.

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