The phenomenon that the content of soluble salts in farmland soil gradually decreases.cropsThe allowable soil salt content for normal growth is called "soil desalination standard".The saline alkali soil can be improved by combining irrigation, washing and drainage with agricultural measures to gradually reduce the salt content of soil in the root layer of crops and reach the desalting standard.[1]
The first step is to utilizeIon exchange membraneTechnology, the cation in seawater is exchanged into ammonium ion through cation membrane, and the cation in seawater is exchanged into ammonium ion through anion membraneanion exchangeIt is carbonate ion, and salt in seawater is converted into ammonium carbonate that can be volatilized;In the second step, the desalting is indirectly realized by decompressing volatilization and/or catalytic decomposition volatilization to precipitate ammonium carbonate.
Multiple effect evaporation
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The operating pressure and boiling point of the solution of the latter evaporator are lower than those of the former evaporator by means of pressure reduction, so that the secondary steam from the former evaporator is used as the heating steam of the latter evaporator, and the heating chamber of the latter evaporator becomes the heating chamber of the former evaporatorcooler。CondensateThe salt in has been removed.
Reverse osmosis method
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reverse osmosisBoth use mechanical pressure to enable water molecules to pass through a special membrane（RO membrane）Fluorine ions cannot be penetrated and removed.After the reform and opening upReverse osmosis technologyMass application in productionpurified waterTherefore, it is also widely used in fluoride removal. This method not only removes toxic and harmful substances that affect human health in water, but also removes minerals and trace elements that are very beneficial to human health.High requirements for water quality pre-treatment require centralized construction of stations for operation, maintenance and management by professionals, and the utilization rate of expensive water is also low {about 50-70%}.If atBrackish waterThe region should also adopt the mixed design of reverse osmosis and defluorocarbon, which can not only solve the taste problem of brackish water, but also make the water contain a certain amount of fluoride and other minerals and trace elements, while also maximizing the utilization of water resources and equipment.
Reverse osmosis method is adopted forInorganic ionThe removal rate of,reverse osmosisThe treated water is justifiable as a temporary thirst quenching water, but it has been proved by relevant experiments at home and abroad that it is not suitable for daily life.
Electrodialysis
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ElectrodialysisLaw was used in the last centurySeawater desalinationAnd salt and bitter water treatment, the principle is toSelectivityThe anion and cation membranes ofelectric fieldFluorine ion in water isMembrane separationIt was removed because of the low utilization rate of water, which was about 45-50%reverse osmosisIt is also low, and improper operation also brings the danger of scaling on the membrane surface and reduces the water production rate.Due to the application of the new EDR integrated technology, the water utilization rate is comparable to that of reverse osmosis, but the requirements for water quality pretreatment are slightly lower than that of reverse osmosis. Therefore, there is still a prospect of application and development.
Forward osmosis method
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"Infiltration" inSeawater desalinationDesalination and water treatmentForward osmosis, is andreverse osmosisA pair of mutually inverse methods.As a potential new technology for water purification and desalination, forward osmosis is being studied theoretically and practically from multiple perspectives and at a deeper level in the world.In 1976, there was an original attempt of liquid-liquid system abroad, and in 1992, the liquid-solid system was invented in Chinaforward osmosisDesalination by (non pressurized) adsorption osmosis (CN92110710.2).It was not until about 10 years later that he followed the international trend again and started the standard imitation and replication mode. In 2008, there was a review report.
Non pressurized Osmosis (1990s)Seawater desalinationLaw, or“Forward osmosis method”, let water pass throughPorous membraneForward osmosis into a super absorbent adsorbent or a solution or solid with a salt concentration even higher than that of seawater does not require external pressure, but the special salt "extract" in the solution is easy to evaporate, and does not need to add too much heat (heating energy andreverse osmosisPressure energy ratio?).It is divided into solid salt and liquid salt directions.Solid saltdesorptionThe additional energy consumption is smaller.
seawater desalination technology Non pressurized adsorption infiltration desalination (CN92110710.2) 1992: Invented by Deng Yu in the 1990s, included in American Chemical Abstracts.
The other two methods are innovative and improved in the film structure
development
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With the rapid development of science and technology, pressure drivenreverse osmosisMembrane separation technology (RO) has made great innovation and improvement in membrane, membrane assembly, equipment and process, but people are increasingly aware of the limitations of RO technology in the field of energy conservation and environmental protection, and in terms of desalination, RO technology can be considered to be close to the peak of development.Therefore, in recent years, foreign countries have carried out "forward osmosis"Membrane separation technology(FO)Seawater desalination, sewage treatment, food processing, medicine and other fields have been applied, especially "pressure delayed osmosis (FRO) seawater power generation", which is a promising clean renewable energy development technology J.However, little attention has been paid to forward osmosis membrane separation technology in China, and there are few related studies and papers.Although, in the 1990s, China had a creative invention of "non pressurized adsorption osmosis seawater desalination" (CN92110710.2).
forward osmosisSeparation technology has been applied for a long time.Long ago, people used salt to store food for a long time, because most bacteria, molds and pathogens in high salt environmentInfiltrationIt will dehydrate to death or lose its activity temporarily.Nowadays, people have begun to use forward osmosisMembrane separation technologyconductSeawater desalinationIndustrial wastewater treatment and garbageOsmotic fluidTreatment;Food industry uses forward osmosis in laboratoryMembrane separationTo concentrate drinks;Emergency rescueLife support systemFresh water is produced by forward osmosis membrane separation technology.Recently, withmaterial science The forward osmosis technology has been applied to the controlled drug release of human body.
