What is the difference between demineralized water, soft water, and deionized water? ? ?

Soft water is water from which hardness elements such as calcium and magnesium ions have been removed; the main methods for achieving this include chemical softening and sodium ion exchange softening； Desalinated water refers to water from which the salts have been removed; it should be considered the same as deionized water. However, deionized water has a higher level of purity, while in desalinated water, depending on the treatment process and the requirements for its use, there are still small amounts of ions present. Examples include primary desalinated water obtained through primary mixed-bed filtration, and secondary desalinated water produced using mixed-bed plus hybrid-bed filtration processes. The treatment methods used include ion exchange, reverse osmosis, and others.

  Is demineralized water soft water with the salt removed further? ? ?   Does salt refer to CL ions and Na ions? ? ?     Is my understanding correct?

Cations in water mainly refer to metal ions, while anions include various salts, non-metal ions, and so on. Softened water primarily removes the cations of alkaline earth metals; (of course, due to issues with measurement methods, it also includes many metal cations that can form complexes with EDTA.) The removal of these ions is what makes water softened. Deionized water, on the other hand, refers to water in which the TDS content has been removed. It’s not just Cl and Na either. But generally, these two are the main components in the TDS content. So it’s basically accurate.

Soft water is water from which calcium and magnesium ions have been removed. Desalinated water is the same as deionized water; it is pure water with no dissolved salts.

Deionized water should contain small amounts of sodium and chloride ions, while softened water refers to water in which the levels of calcium and magnesium have been reduced to certain values. Deionized water refers to water in which all metal ions and anions have been reduced to certain levels.

Softened water only reduces hardness, while demineralized water not only reduces hardness but also lowers salt content

Soft water mainly removes soluble calcium and magnesium compounds from water, or eliminates most of such compounds； Deionized water is water from which the substances present in ionic form, or most of those substances in ionic form, have been removed; this naturally includes soluble calcium and magnesium ions as well ； Deionized water is water that contains very few or no minerals; it has been treated using cation and anion exchangers, resulting in the removal of virtually all cations and anions from the water.         Soft water: 1. What is soft water? Water that contains little or no soluble calcium and magnesium compounds is called soft water. Soft water does not easily form scum with soap, unlike hard water. Natural soft water generally refers to water from rivers, streams, and lakes (freshwater lakes). Softened hard water refers to water that has had its calcium and magnesium salts reduced to levels of 1.0–50 milligrams per liter. Although boiling can turn temporarily hard water into soft water, it is extremely uneconomical to use this method for treating large amounts of water on an industrial scale.   2. The methods for preparing softened water are: ① Lime-soda method. First, the hardness of the water is determined, after which a fixed amount of calcium hydroxide and sodium carbonate is added; the calcium and magnesium ions in the hard water then precipitate out. 　　Ca(HCO3)2 + Ca(OH)2 = 2CaCO3↓ + 2H2O 　　② Phosphate softening method. For boiler water, sodium phosphite (NaPO3) can be added as a water softener; it forms complexes with calcium and magnesium ions, preventing these ions from precipitating out when the water is boiled, and thus avoiding the formation of scale. This method is not suitable for softening drinking water. 　　Mg(HCO3)2 + 2Ca(OH)2 = Mg(OH)2↓ + 2CaCO3↓ + 2H2O 　　③ Ion exchange method. Although both zeolites and ion exchangers are insoluble in water, the sodium and hydrogen ions contained in them can undergo exchange reactions with the calcium and magnesium ions in hard water, causing these ions to be adsorbed by the zeolites, artificial zeolites, and ion exchangers and thus removed. Zeolites and ion exchangers that become ineffective after long-term use can be reused through regeneration; therefore, this method is an economical and advanced approach for water softening. 　　CaSO4 + Na2CO3 = CaCO3↓ + Na2SO4 　　Method 4: Adding specialized scale inhibitors to water can alter the way calcium and magnesium ions combine with carbonate ions, thereby preventing the formation and deposition of scale. There are many scale inhibitors available for industrial use today. The advantage of this method is that it requires less initial investment and has wide adaptability ； However, the operating costs are high when the water volume is large and soft; due to the addition of chemicals, its use is heavily restricted, and it generally cannot be used for drinking, food processing, industrial production, and other purposes. It is also rarely used in the civilian sector. 　　5 Electromagnetic method: This involves applying a certain electric or magnetic field in water to alter the properties of ions, thereby changing the rate of deposition of calcium carbonate (magnesium carbonate) as well as its physical properties during deposition, and thus preventing the formation of hard water scale. Its features are: low equipment investment, easy installation, and low operating costs ； However, its effectiveness lacks stability, and there are no uniform criteria for measurement. Moreover, since its main function is merely to affect the physical properties of scale within a certain range, the duration for which the treated water can be used and the distance over which it can be utilized are limited. It is mainly used for the treatment of circulating cooling water in commercial applications such as central air conditioning, and cannot be used for the treatment of water used in industrial production or as boiler make-up water (as the mechanism behind this type of equipment has not been truly theoretically proven). 　　6 Membrane separation method: Both nanofiltration membranes (NF) and reverse osmosis membranes (RO) can remove calcium and magnesium ions from water, thereby significantly reducing water hardness. The advantage of this method is that it yields significant and stable results, and the treated water can be used in a wide range of applications ； However, it requires a high inlet water pressure, and both the equipment investment and operating costs are high. It is generally used less often, and is mostly applied in specialized softening treatments. II: Deionized Water Deionized Water: Deionized water refers to pure water from which impurities in ionic form have been removed. The definition of “deionized” as specified by the International Organization for Standardization ISO/TC 147 is: “Deionized water has had ionic substances removed from it, either completely or partially, primarily through the use of ion exchange resin treatment.” ” 　　Ion exchange resins are used to remove anions and cations from water, but soluble organic substances still remain in the water; these can contaminate the ion exchange columns and reduce their efficiency. Deionized water is also prone to bacterial growth when stored. 　　To convert tap water into deionized water, several treatment steps are generally required: first, coarse impurities are removed through quartz sand filtration; then ions are removed sequentially using cation and anion exchange columns; after that, the water is forced through a reverse osmosis membrane. Finally, ultraviolet treatment is usually applied to eliminate microorganisms in the water. If the resistivity still does not meet the required standards, ion exchange and reverse osmosis processes can be repeated. Distilled water, on the other hand, is obtained by vaporizing water and then condensing it, and its purity is generally lower than that of deionized water. In the semiconductor industry, deionized water is used the most. The system process flow is as follows: tap water --> pre-treatment --> activated carbon --> safety filtration --> reverse osmosis --> electro-deionization to produce demineralized water. Demineralized water contains very little or no minerals, and this can be achieved through distillation, reverse osmosis, ion exchange, or a combination of these methods. This post was last edited by qqjmycq on 2009-3-17 16:41]

The mineral content is arranged from low to high, deionized water

Firstly, soft water is a concept that relates to water hardness; water hardness generally refers to the total amount of calcium and magnesium ions. Soft water is achieved by converting most of these calcium and magnesium ions into other ions (usually sodium ions), while the other ions remain essentially unchanged. The concepts of desalinated water and deionized water are essentially the same; here, \"salt\" refers to substances in a broad sense that can ionize into positive and negative ions in water. Therefore, desalination and deionization are essentially identical.

Demineralized water is used primarily to remove metal cations, oxides, and other compounds; deionized water removes both cations and anions; while soft water is water that contains fewer soluble calcium and magnesium compounds

The people above have said a lot, and basically everything they said is correct, but it’s not clear. Soft water refers to water in which the cations have been removed using cation exchange resins; the goal is primarily to reduce the hardness of the water. Soft water treatment units used in small boilers operate on this principle, as these cations tend to deposit on the inner walls of the boiler, leading to scaling over time, increased energy consumption, and even elevated boiler pressure, which can pose safety risks. Therefore, it is necessary to use soft water. For simplicity, small boilers rely on this method, but boilers in power plants work entirely differently. Pure water refers to water with a conductivity of 10 or less, obtained through treatment using cation exchange resins, as well as reverse osmosis and electrodialysis processes. It is used in laboratories or in situations where high standards of analysis are required. Food and pharmaceutical companies also need to use pure water in order to prevent impurities from entering their products, thereby ensuring the purity and quality of those products. Desalinated water is a general term that usually lacks a precise definition; formal documents do not use such an informal term to describe water quality requirements.

Soft water is water in which calcium and magnesium ions have been removed through ion exchange; it is generally used to reduce water hardness and is suitable for low-pressure boilers. Deionized water and ionized water are treated through membranes to reduce the water’s conductivity to less than 20 us; it is suitable for large boiler systems with steam generation units that have high performance requirements.