Calcium hard water

Detergents are designed to be effective in hard water meaning water containing calcium salts that form insoluble calcium carboxylates with soaps These precipitates rob the soap of Its cleansing power and form an unpleasant scum The calcium salts of synthetic deter gents such as sodium lauryl sulfate however are soluble and retain their micelle forming ability even m hard water... 

Ca.ndy. Its low melting point and sugar inversion properties make malic acid a desirable acidulant, especially in hard candy products (44,45). Due to their insolubiUty, hard water salts can cause clouding of the finished product. However, because of the higher solubiUty of calcium malate [17482-42-7] relative to alternative acidulants, clarity of the finished product is enhanced. Additionally, in sugar confectionery products where acidulation may exceed 2.0%, malic acid can provide economic benefits. 

Calcium carbonate (calcite) scale formation in hard water can be prevented by the addition of a small amount of soluble polyphosphate in a process known as threshold treatment. The polyphosphate sorbs to the face of the calcite nuclei and further growth is blocked. Polyphosphates can also inhibit the corrosion of metals by the sorption of the phosphate onto a thin calcite film that deposits onto the metal surface. When the polyphosphate is present, a protective anodic polarization results. 

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). 

Makeup. Makeup treatment depends extensively on the source water. Some steam systems use municipal water as a source. These systems may require dechlorination followed by reverse osmosis (qv) and ion exchange. Other systems use weUwater. In hard water areas, these systems include softening before further purification. Surface waters may require removal of suspended soHds by sedimentation (qv), coagulation, flocculation, and filtration. Calcium may be reduced by precipitation softening or lime softening. Organic contaminants can be removed by absorption on activated carbon. Details of makeup water treatment may be found in many handbooks (22—24) as well as in technical Hterature from water treatment chemical suppHers. 

To improve magnesium reduction, which also improves siHca reduction in cold process softening, sodium aluminate may be used. The sodium aluminate provides hydroxyl ion (OH ) needed for improved magnesium reduction, without increasing calcium hardness in the treated water. In addition, the hydrolysis of sodium aluminate results in the formation of aluminum hydroxide, which aids in floe formation, sludge blanket conditioning, and siHca reduction. 

A negative attribute of orthophosphate is its tendency to precipitate with calcium hardness found ia natural waters. In recent years, deposit control agents that prevent this deposition have been developed. Owiag to its relatively low cost, orthophosphate is widely used as an iadustrial corrosion inhibitor. 

Sodium C rbon te. Sodium carbonate softens water by forming insoluble calcium carbonate with calcium ions in hard water. Carbonate can also reduce calcium levels by ion pairing, although the benefit to detergency is questionable. Buildup of calcium carbonate on machine and fabrics, which can occur with time, is undesirable. Sodium carbonate [497-19-8] does not provide any suspending action. It does, however, provide alkalinity to the wash hquor and is an effective alkah. 

Hardness leakage is also dependent on the raw water characteristics. If the Na/Ca ratio and calcium hardness are very high in the raw water, leakage of the hardness ions will be higher. 

The speciality chemical LifXTl (40% "CP) is used when calcium is contra-indicated,. such as in the. sanitation of hard water and in. some dairy applications. Some idea of the scale of these applications cati be gained from the following production figures which relate to the USA ... 

Lucey examined a number of examples of pitting of copper pipes and tanks from hard water districts, and found that there was no more calcium carbonate scale deposited around the pits than on other parts of the metal surface. There was, however, a large amount of CaCOs in the mound... 

Of the dissolved gases occurring in water, oxygen occupies a special position as it stimulates the corrosion reaction. Carbon dioxide is scarcely less important this constituent must, however, be considered in relation to other constituents, especially calcium hardness. 

Very hard waters are usually not very aggressive provided that they are supersaturated with calcium carbonate. Underground waters with a low pH value and high carbon dioxide content are, however, aggressive unless corrective treatment is applied. 

The most important property of the dissolved solids in fresh waters is whether or not they are such as to lead to the deposition of a protective film on the steel that will impede rusting. This is determined mainly by the amount of carbon dioxide dissolved in the water, so that the equilibrium between calcium carbonate, calcium bicarbonate and carbon dioxide, which has been studied by Tillmans and Heublein and others, is of fundamental significance. Since hard waters are more likely to deposit a protective calcareous scale than soft waters, they tend as a class to be less aggressive than these indeed, soft waters can often be rendered less corrosive by the simple expedient of treating them with lime (Section 2.3). 

The effect of pH on the corrosion of zinc has already been mentioned (p. 4.170). In the range of pH values from 5 -5 to 12, zinc is quite stable, and since most natural waters come within this range little difficulty is encountered in respect of pH. The pH does, however, affect the scale-forming properties of hard water (see Section 2.3 for a discussion of the Langelier index). If the pH is below the value at which the water is in equilibrium with calcium carbonate, the calcium carbonate will tend to dissolve rather than form a scale. The same effect is produced in the presence of considerable amounts of carbon dioxide, which also favours the dissolution of calcium carbonate. In addition, it is important to note that small amounts of metallic impurities (particularly copper) in the water can cause quite severe corrosion, and as little as 0-05 p.p.m. of copper in a domestic water system can be a source of considerable trouble with galvanised tanks and pipes. 

Silicates at about 20-40 p.p.m. are also used in cooling-water treatment although the build-up of protection can be slow. At higher temperatures calcium silicate may be deposited from hard waters. 

Calcareous Scale a scale consisting largely of calcium carbonate and magnesium hydroxide which may be precipitated from a hard water. 

Provision of pretreatment The initial fill volume and MU supply is almost always pretreated in some manner. Because of the large volume of water in these systems, even low-hardness waters can produce sufficient quantities of calcium carbonate scale to severely impede heat transfer thus, for MTHW pretreatment, the use of ion-exchange softeners is the norm. For HTHW, some form of demineralization such as reverse osmosis (RO) or deionization by cation-anion exchange is typically preferred. 

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