What are the Chemical Properties of Seawater?

Sea water is water in or from the sea. Seawater is flowing, and for humans, the amount of water available is unlimited. Seawater is a veritable liquid mineral. There are 35.7 million tons of minerals per cubic kilometer of seawater. Of the more than 100 elements known in the world, 80% can be found in seawater. Seawater is also the source of freshwater on the land and the regulator of the climate. The world s oceans evaporate 4.5 million cubic kilometers of freshwater each year, 90% of which return to the ocean through rainfall, 10% become rain and snow on the ground, and then return to the river along the river . Desalination technology is developing into an industry. Some people predict that with the deterioration of the ecological environment, the last way for humans to resolve water shortages is likely to be desalination of seawater.

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(1) [seawater]: Water in or from the sea. Bright

Why is it salty

According to statistics, among those killed at sea, those who drink seawater have a 12 times higher mortality rate than those who do not drink seawater. Why is this? It turns out that the human body needs to discharge about 150 grams of water in order to discharge 100 grams of salt contained in seawater. Therefore, people who drink seawater not only can't replenish the water needed by the human body, but dehydrate quickly, and eventually cause death.

Seawater is drinkable after desalination. There are dozens of methods of desalination, the most important of which are

Desalination Technology: Non-Pressurized Adsorption Osmotic Desalination

Included in "American Chemical Abstracts" in the 1990s

Ingesting Ocean Sweet Spring

Water is the source of life. Not long ago, humans were obsessed with the myth that freshwater is an inexhaustible gift in nature. However, the booming industrialization and the sharp increase in population have ruthlessly crushed this myth. The freshwater crisis is even more threatening than the food crisis and oil crisis.

At first, scientists believed that seawater was inherent to the earth. They start with

Sea salt

China's sea salt production has developed rapidly. There are salt fields in 11 coastal provinces, autonomous regions, and municipalities. The area of salt fields has increased significantly compared to the early days of the People's Republic of China. The quality of the produced sea salt has also been continuously improved, with more and more varieties. In addition to raw salt, washing salt, crushed washing salt, refined salt, iodized salt, table salt, casing salt, egg yolk salt and fine beach salt have been put into mass production. .

Seawater fertilizer

Potassium is sixth in seawater, with a total of 600 trillion tons. Potassium chloride is a fertilizer we extract from seawater. Potassium fertilizers have fast effects, are easily absorbed by plants, and are not easy to lose. Potassium fertilizer can make crop stalks grow strong, prevent lodging, promote flowering and firmness, and enhance cold and disease resistance. Potassium extraction in seawater is mainly used to make potassium fertilizer. In addition, potassium is used industrially to make potassium-containing glass, which is not susceptible to chemical corrosion and is often used in the manufacture of chemical instruments and decorations. Potassium also makes soap and can be used as a detergent. Potassium alum (alum) can be used as a water purification agent.

Bromine extraction from seawater

The vast sea is the "hometown" of the chemical element bromine. More than 99% of the bromine on the earth is in seawater, which can be described as the source of bromine in the sea. The bromine content in seawater is about 65 mg / liter, with a total of 100 trillion tons.

China began to use the "air blowing method" for direct bromine extraction from seawater in 1967, and succeeded in 1968. Qingdao, Lianyungang, Beihai, Guangxi and other places have successively established bromine extraction plants for trial production. The "resin adsorption method" for bromine extraction from seawater was also successfully tested in 1972.

Why not filter salt from seawater to get drinking water?

Why not filter salt from seawater to get drinking water?

Diluted energy

Considering the vast water resources contained in the earth's oceans, desalination can only meet less than 0.5% of the total human drinking water demand. Humans need a total of 960 cubic miles (4,000 cubic kilometers) of fresh water each year. Generally, the surface fresh water is sufficient to meet the needs. However, there is a regional lack of drinking water. So why don't we desalinate more water to alleviate water shortages and conflicts over water use?

The problem is that desalination requires a lot of energy. Salt dissolves very easily in water, and the chemical bonds formed are difficult to break. Both energy and desalination technologies are very expensive, which means that desalination will be an expensive technical approach.

In fact, it is not easy to estimate the cost of desalination-this number is closely related to the region, labor prices, energy costs, land costs, financial financing costs, and even the salt content of seawater. The cost of desalination of 1 cubic meter (264 gallons) of seawater can range from less than $ 1 to more than $ 2.

If you collect water from rivers or underground, the cost will plummet to 10-20%, and farmers usually spend very little on water.

This means that local freshwater is always much cheaper than desalination. Although from a trend perspective, the gap between prices is decreasing. For example, by finding new water sources or building dams to meet drinking water needs in places like California, the cost per cubic meter is equivalent to 60% of the cost of desalination.

Unfortunately, sometimes this traditional method of obtaining drinking water is no longer effective. In addition, the cost of obtaining water is rising, so that places like California are seriously considering whether to obtain drinking water through desalination, and places like Tampa, Florida have decided to build the nation's largest desalination plant.

According to data provided by the International Desalination Association, in 2007 there were approximately 13,000 desalination plants in the world working. These plants produce approximately 14.7 billion gallons (55.6 billion liters) of potable fresh water per day. Most factories are located in places like Saudi Arabia where water is more expensive than oil.

The role of energy in desalination technology

There are two ways to break saltwater chemical bonds in seawater: the thermal evaporation method and the thin film infiltration method. The hot steaming method requires heat: the sea water is boiled, the water evaporates to leave salt, and then the water vapor is cooled to obtain liquid fresh water.

The most common method of membrane osmosis is called reverse osmosis. Use a semi-permeable membrane to separate water and salt from the seawater. Because this technology is cheaper than the lift-off method, most desalination plants use this method. For example, Tampa's desalination plant uses reverse osmosis to desalinate seawater.

It should be noted that the desalination of seawater also entails environmental costs. With the seawater entering the desalination plant, marine life will be destroyed, and some marine life such as small fish and plankton will destroy the food chain in the ocean. In addition, how to deal with the high-purity salt produced by seawater desalination is also a headache. If these highly saline wastewaters are discharged into the sea, local aquatic crops could be severely harmed. It is not difficult to deal with these environmental issues, but it will increase the cost of desalination.

Despite economic and environmental problems, desalination is beginning to show attractive advantages as humans run out of other water sources. Humans have already over-exploited surface water, and there are various dams on the ground that are beyond the economic and environmental capacity. As long as they are available rivers, humans will block them.

Although there is still much work to be done to effectively and rationally use existing water sources, as the world's population grows and water supply shrinks, desalination will become more and more popular.