Water, softening effect

Figure 3.18. Influence of NaCl on the water-softening effect and the washing performance of zeolite A water-softening effect at measured 90°C after 15 min washing performance measured at 90°C and 285 ppm water hardness on particulate-sebum-soiled cotton (14)...

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. 

The organic acid salts, such as EDTA and heptonate, are included for water softening properties, and to assist in the removal of solid particles. Gluconate and heptonate, in particular, are effective in the highly alkaline solutions used for etching aluminium and prevent the precipitation of aluminium hydroxide scale and sludge. 

In almost all industrial circumstances, a deaerator is a cost-effective oxygen-removing proposition that complements primary pretreatment equipment such as water softeners. 

Therefore, to minimize the certainty of waterside carbonate deposition, essentially all types of steam generating boilers should be provided with a water softener or some other equally effective form of pretreatment equipment. 

It is difficult to manage the problem of high sludge production in lower pressure boilers where precipitation programs, especially carbonate conditioning, are used because it has a knock-on effect resulting in condensate line corrosion. The answer is always to install a water softener. The payback time is very short because of the reduced BD necessary as a result of decreased sludge production. 

Pentasodium pentetate, tetrasodium etidronate, and tetra-sodium EDTA are added as water softeners and to protect the dyes and perfumes from the effects of metal ions in the mixtures. These compounds lock up calcium and magnesium in the water, preventing them from reacting with the soap to form insoluble soap scum. 

Ion exchange is effective for the removal of cationic or anionic heavy metal contaminants. It can also be used for water softening. Ion-exchange resins are usually regenerable with salt.65... 

Water softener manufacturers remind us of the many undesirable effects produced by hard water. Besides enhancing the likelihood of harmful scale deposits in plumbing, water heaters, and dishwashers, hard water also has been associated with bathtub scum, deposits on laundry, scale on glasses and dishes, scratchy skin, and unmanageable hair. A simple chemical process explains the origin of hard water. Additional chemical reactions provide an explanation for the scum and deposits that readily form when soap and hard water combine. 

Sodium tripolyphosphate is the main phosphate found in detergents. It acts as a water softener and counteracts the elements that are responsible for hard water while at the same time making the detergent a more effective cleaner. 

The fact that most triphosphates of polyvalent cations which are difficultly soluble in water are soluble in excess of triphosphate, and that such polyvalent cations (e.g. Ca++) are either not precipitated or not quantitatively precipitated by the usual reagents from solutions of their salts containing triphosphate, has become of great commercial importance in water softening (90). The term sequestration is used in this connection. Numerous publications have appeared which are not mentioned in detail here, and which attempt to determine this property quantitatively. In general, the effect is attributed to the formation of relatively stable ion pairs or complexes, the stability of which is defined by the formation constants K or K. ... 

NF is used when high molecular weight solutes have to be separated from a solvent. It is effective in the production of drinking water, especially in the case of water softening. Compared to RO, a lower retention is found for monovalent ions. But very recently [9], it has been found that NF separates the ions of the same valency for a selective defluorination of brackish water. RO and UF have shown, respectively, solution-diffusion and convection mass transfers. In NF, a synergism between both can be observed but strongly depends on the operational conditions (pH, ionic strength, flow rate, transmembrane pressure) and on the membrane material used. 

Caustic soda will convert the magnesium salts into the still less soluble hydroxide and thus soften the water more effectively.1 If sufficient free carbon dioxide is present, dissolved in the water, caustic soda, or a mixture of sodium carbonate and milk of lime, may with advantage be added instead of sodium carbonate, as it is transformed into this latter salt by the carbon dioxide, and then reacts according to the above equations. This fixes the dissolved carbon dioxide and prevents it from converting into bicarbonates the normal carbonates precipitated when sodium carbonate is first used, and thereby converting a permanently hard water into one possessing temporary hardness. 

Sodium is present in soils and water as NaCl. In arid environments, NaCl accumulates in the surface and groundwater owing to irrigation and high evapotranspiration. Other activities such as road salting and water softening may also contribute NaCl to natural waters. For additional information on human health effects and drinking water levels, see Shelton (1989). 

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