Softening water

Hard water can be softened by several methods which vary in efficiency and cost. Distillation will result in water free of dissolved salts and nonvolatile organic substances. This can be carried out using solar energy, and many devices have been described whereby seawater can be converted into potable drinking water, usually on a small scale. 

Water frozen slowly will be free of dissolved organic and inorganic compounds. The freeze-thaw cycle is used to purify semiconductors by the process called zone refining. Fog and dew have also been used as sources of freshwater. 

The removal of the Ca/Mg hardness can be effected by the lime process. In this process, lime (as CaO or Ca(OH)2) is reacted with Ca(HC03)2 or Mg(HC03)2 to form CaCOs and Mg(OH)2, respectively  

Lime to be added is calculated from the measured Ca/Mg hardness and adjusted to a pH of 9-9.5 for calcium removal, but a pH of about 12 is needed to remove most of the Mg . 

Water is softened to remove the scale-forming hardness elements. Soft water is required for boilers, water heaters, cooling towers, reverse osmosis systems, etc. Softening is an ion-exchange process which replaces almost all of the metallic or cations by sodium ions and sometimes, the anions with chlorine ions. Therefore, a constant supply of salt is required. 

A softener may be used in conjunction with a deionizer on certain water supplies to provide softened water for use in regeneration. This will prevent the formation of insoluble precipitates within the deionizer resin bed. 

It is important to note that softening does not remove silica, which forms a very hard scale that is not easily removed. In addition, softening does not remove chloride which can cause stress corrosion cracldng in stainless steel. 

Softeners can be a microbial concern. A dark and moist column interior can provide a growth environment. The regeneration cycle which uses concentrated brine solution and a backwash cycle aids in reducing the bioburden. Softeners should be regenerated based on a time clock set for twice weekly regenerations and on a volumetric flow of water, whichever is shorter. Since the regeneration cycle removes the softener bed from operation, a dual bed system is often specified. 

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A salt originally called sodium hexametaphosphate, with n believed to be 6, is now thought to contain many much larger anion aggregates. It has the important property that it sequesters , i.e. removes, calcium ions from solution. Hence it is much used as a water-softener. 

Phosphorus is also important in the production of steels, phosphor bronze, and many other products. Trisodium phosphate is important as a cleaning agent, as a water softener, and for preventing boiler scale and corrosion of pipes and boiler tubes. 

Water, sewage Water softeners Water softening... 

Ton-exchange systems vary from simple one-column units, as used in water softening, to numerous arrays of cation and anion exchangers which are dependent upon the appHcation, quaHty of effluent required, and design parameters. An Hlustration of some of these systems, as used in the production of deionized (demineralized) water, is presented in Figure 7. 

Zeohtes have high potential for protecting ecosystems, from faciUtating wastewater and gas treatment to providing water softeners in detergents to replace the undesirable polyphosphate. 

Trisodium phosphate is strongly alkaline many of its appHcations depend on this property. For example, many heavy-duty cleaning compositions contain trisodium phosphate as a primary alkalinity source. The crystalline dodecahydrate itself is marketed as a cleaning compound and paint remover. Traditionally, trisodium phosphate has been used in water softening to remove polyvalent metal ions by precipitation as insoluble phosphates. Because the hypochlorite complex of trisodium phosphate provides solutions that are strongly alkaline and contain active chlorine, it is used in disinfectant cleaners, scouring powders, and automatic dishwashing formulations. 

ZeoHte-based materials are extremely versatile uses include detergent manufacture, ion-exchange resins (ie, water softeners), catalytic appHcations in the petroleum industry, separation processes (ie, molecular sieves), and as an adsorbent for water, carbon dioxide, mercaptans, and hydrogen sulfide. 

Sodium alumiaate is used ia the treatment of iadustrial and municipal water suppHes and the use of sodium alumiaate is approved ia the clarification of drinking water. The FDA approves the use of sodium alumiaate ia steam generation systems where the steam contacts food. One early use of sodium alumiaate was ia lime softening processes, where it iacreases the precipitation of ions contributing to hardness and improves suspended soHds removal from the treated water (17). Sodium alumiaate reacts with siHca to leave very low residual concentrations of siHca ia hot process water softeners. Sodium alumiaate is often used with other chemicals such as alum, ferric salts, clays, and polyelectrolytes, as a coagulant aid (18,19). 

Centrifugal casting is used to produce water softener tanks and pipe by saturating a reinforcement with thermosetting resin within a mold that is then rotated at high speed to consoHdate the laminate before curing. 

Similar to processing mined rock salt, solar salt may be cmshed, screened, and kiln dried or fluidized-bed dried. Coarse solar salt is a premium product because of high purity and relatively large crystal size. It is in particular demand for use to regenerate the resin in cation-exchange water softeners... 

Sales of salt for regenerating ion-exchange water softeners have grown steadily in the United States, particularly in terms of revenues. The U.S. salt industry is mature and sales are not likely to increase rapidly. The dry salt industry in the United States and Canada has undergone consoHdation during the 1990s. The number of producers has continued to decline as the major salt producers have acquired smaller operations. Table 6 shows the total amount, including salt in brine, of salt sold or used in the United States for the period 1990—1994. The amount of salt sold or used in the United States in 1994 by product type is (9) ... 

Water is softened by removing calcium and magnesium ions from hard water in exchange for sodium ions at sites on cation-exchange resin. Water softeners typically use a gel polystyrene sulfonate cation-exchange resin regenerated with a 10% salt brine solution (25). 

Ring-and-ball method (ASTM D36-26). In the United States, two other softening point methods ate employed cube-in-air (35) and cube-in-water (36). Cube-in-air softening point = R-and-B softening point +4 C. Cube-in-water softening point = R-and-B softening point +10 C. 

Home desalinators are possible only for industrialized countries with a central service organization. They will eventually become available on a rental/service contract basis, as is standard practice for water softeners in many communities. Although rental of water softeners is common in the United States, home membrane-system rental is not estabUshed. 

Today most salt is used to make caustic soda and chlorine (see Alkali and chlorine products, chlorine and sodiumhydroxide). These chemicals are used in thousands of household products. The next biggest use is for highway deicing. Other uses are for water softening, Hvestock feeds, meat packing, and foodstuffs. 

Appllca.tlons. The principal uses are in scouring cleansers and acid metal cleaners for dairy equipment. Use in dishwasher detergents has been supplanted by chlorinated isocyanurates, which are more cost-effective, more stable in hot water, and possess water softening properties. 

Tetrasodium pyrophosphate [7722-88-5] Na4P20y, is another important primary builder and detergent. In sequestration, it is not quite as effective as sodium tripolyphosphate and its usage in heavy-duty laundry powders has declined in recent years. Functionally, tetrasodium pyrophosphate is both a builder for surfactants (ie, water softener) and alkaH. 

Similarly, installed costs of water-softening systems can be correlated in United States dollars (M S = 1000) as follows ... 

Ion exchange may be thought of as a reversible reaction involving chemically equivalent quantities. A common example for cation exchange is the familiar water-softening reaction... 

Ion exchange (electrostatic) Equihbrium Deionization Water softening Rare earth separations Recovery and separation of pharmaceuticals (e.g., amino acids, proteins)... 

Sharp Metallic Smell a) Water softener can remove 0.5 ppm or iron (Fe) for every grain/gal. of hardness up to 10 ppm at minimum pH of 6.7 (unaerated water)... 

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