Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, since soap is not wasted to clean calcium ions. Soft water also extends the life of the pipe by reducing or eliminating crust buildup in pipes and fittings. Water softening is usually achieved using lime softening or ion exchange resin.
Video Water softening
Rationale
The presence of certain metal ions such as calcium and magnesium, especially as bicarbonate, chloride, and sulfate in water cause various problems.
Hard water leads to limescale buildup, which can cause pipes, and increase galvanic corrosion. In the industrial scale of water softening plants, the waste stream from the re-generation process can precipitate scales that can disrupt the waste disposal system.
The slippery feeling experienced when using soap with soft water occurs because soap tends to bind fat in the skin's surface layer, making soap molecules difficult to remove with simple dilution. Conversely, in areas of hard water, rinse water contains calcium or magnesium ions that form insoluble salts, effectively removing the residual soap from the skin but potentially leaving a non-soluble stearate layer on the surface of the bath and shower, commonly called soap scum.
The desires of these competing effects vary according to personal preference and those who do not like soft water effects may choose to harden water by adding chemicals such as baking soda, calcium chloride, or magnesium sulfate.
Maps Water softening
Method
The most common way to remove water hardness depends on ion exchange resins or reverse osmosis. Other approaches include precipitation and sequestration methods with the addition of chelating agents.
Ion exchange resin device
Conventional water softening devices intended for domestic use depend on ion exchange resins in which "hardness ions" - especially Ca 2 and Mg 2 - are exchanged for sodium ions. As described by NSF/ANSI Standard 44, ion exchange devices reduce hardness by replacing magnesium and calcium (Mg 2 and Ca 2 ) with sodium or potassium ions (Na and K ). "
The ion exchange resin is an organic polymer containing anionic functional group in which the divalent cation (Ca ) binds more strongly than the monovalent cation (Na ). Inorganic matter called zeolite â € <â € When all available Na ions have been replaced with calcium or magnesium ions, the resins must be replenished by eluting Ca 2 and Mg 2 ions using sodium solution chloride or sodium hydroxide, depending on the type of resin used. For anionic resins, regeneration usually uses a solution, sodium hydroxide (alkali) or potassium hydroxide. The waste water eluted from the ion exchange columns containing calcium and unwanted magnesium salts is usually discharged into the sewage system. Lime softening
The softening of lime is a process in which lime is added to hard water to make it softer. It has several advantages over ion exchange methods but is especially suited for commercial care applications.
Chelating agents Chelating agents
Chelators are used in chemical analysis, as water softeners, and are an ingredient in many commercial products such as shampoos and food preservatives. Citric acid is used to soften water in soaps, personal care products and detergents. Commonly used synthetic chelates are ethylenediaminetetraacetic acid (EDTA), which may be present as tetrasodium or disodium salts. Due to the environmental and aquatic toxicity issues concerning the widespread use of EDTA in household and personal care products, alternatives such as sodium phytate/tetrachodium glutamate diacetate and trisodium ethylenediamine disuccinate find more general use.
Distillation and rain water
Because Ca 2 and Mg 2 exist as nonvolatile salts, they can be removed by distilling water. Distillation is too expensive in most cases. Soft rainwater is naturally distilled during evaporation, condensation and sedimentation cycles.
Reverse osmosis
Reverse osmosis (RO) takes advantage of a hydrostatic pressure gradient across a special membrane. The membrane has pores large enough to accept water molecules to pass; hard ions such as Ca 2 and Mg 2 remain behind and discharged by excess water into the drain. The resulting soft water supply is free of violent ions without any other ions being added. Membranes are a type of water filter that requires regular cleaning or replacement care.
Non-chemical devices
Some manufacturers claim that their electronic devices affect the interaction of minerals with water so that the minerals do not bind the surface. Because this system does not work with ion exchange, such as traditional water softeners, one benefit that is claimed for the user is the elimination of the need to add salt to the system. While reductions in particle size and the promotion of plant growth have been claimed, such a system does not remove minerals from the water itself. Instead, they can only change the downstream effects that mineral water should have. Examples are remediation of calcium scale and remediation of salt crust on the ground. This system is not included in the term "water softening" but "water conditioning".
Similar claims for magnetic water treatment are not considered valid. For example, no reduction in scale formation was found when the magnet device was scientifically tested.
The above method, distillation and reverse osmosis, are two of the most widely used non-chemical water softening methods.
Health effects
The CDC recommends limiting daily total sodium intake to 2,300 mg per day, although the average American consumes 3,500 mg per day. Since the amount of sodium present in drinking water - even after softening - does not represent a significant percentage of one's daily sodium intake, the EPA considers sodium in drinking water unlikely to cause adverse health effects.
For those who are on a sodium-restricted diet, the use of a reverse osmosis system for drinking water and boiling water will remove sodium along with other possible impurities. Potassium chloride can also be used as regeneration rather than sodium chloride, although it is more expensive. For people with impaired renal function, however, elevated levels of potassium, or hyperkalemia, can cause complications such as cardiac arrhythmias.
Compared to reverse osmosis and the distilled method of producing soft water, hard water provides several health benefits by reducing the solubility of toxic metal ions such as lead and copper, which are more soluble in soft water than in hard water.
Environmental impact
Softened water (measured as the remaining sodium carbonate index) where calcium and magnesium have been partially replaced by sodium is not suitable for irrigation use, as it tends to lead to the development of alkaline soils. Non-chemical devices are often used as a substitute for traditional water softening for this application.
See also
- Desalination
- Ion exchange
- Water purification
References
Source of the article : Wikipedia
0 Comments