Water hardness salts

Calcium ion enters the system not ordy in the form of water hardness but also in the form of calcium salts contained in the sod. Other heavy-metal ions such as aluminum and ferric iron may also be present in the sod, and must be removed by an appropriate budder to achieve good sod removal. Effective budders for cotton washing are those for which the calcium dissociation constant, expressed as or —logif -, is >4 and preferably >7 (33). 

The base exchange process removes both the temporary and permanent hardness salts from the water by allowing the water to flow through resin beads containing sodium zeolite, Na2Z. 

Basically, the hardness salts of calcium and magnesium ions are ex changed for sodium ions in the dealkization process the carbonate and bicarbonate salts, which cause high levels of alkalinity, are replaced with chloride ions. Reverse osmosis can also be used to produce demineralized water. 

Water hardness The hardness of a water sample due to the salt content. 

Water, softening A chemical process used to change the chemical composition of water by the removal of hardness salts. 

A colorless, colloidal precipitate was formed and stirred thoroughly for about 15 minutes, whereupon it was filtered by suction. The raw product thus obtained was washed with water until It contained only about Va% water-soluble salts. After drying for 12 hours In a vacuum apparatus at 60°C and under a pressure of 12 mm Hg, the product had the form of hard pieces. The pieces were comminuted to powder in a ball mill and the powder was passed through a sieve (3,600 meshes per cm ). The small residue on the sieve was again pulverized and passed through the same sieve. The yield was 870 g, or 99% of theoretical, calculated on the assumed formula... 

LSI (Langelier Saturation Index) an indication of the corrosive (negative) or scale-forming (positive) tendencies of the water. Hardness the total dissolved calcium and magnesium salts in water. Compounds of these two elements are responsible for most scale deposits. Units are mg/l as CaCOs. 

Carbon dioxide, from the decomposition in the boiler of temporary hardness salts present in some waters, causes corrosion of steel steam pipework and cast iron valves and traps. Corrosion inhibitors may be used, but the choice of inhibitor must take into account the other materials in the system. Neutralizing amines such as morpholine or cyclohexylamine are commonly used. 

Upland surface water. This is low in hardness salts having run over impervious rocks but will often be high in organic matter, i.e. fulvic and humic acids. 

Treatment of waters for boiler feed For most boilers, then, raw water from any of the above sources will require treatment followed by appropriate conditioning. In simple, low pressure plants, precipitation of the hardness salts, e.g. by lime or lime/soda, will be adequate. 

As has been noted, scaling due to inadequate water treatment may, in the short term, lead to efficiency losses but, eventually, could result in overheating and possibly to associated corrosion. Awareness of this has led to an increasing use of appropriate water treatment with increasing boiler pressure. Scaling due to hardness salts is therefore less common now than formerly, but deposits caused by other means may occur with similarly undesirable consequences. 

With high-pressure boilers operating above about 60 bar, the complete removal of hardness salts from the feed-water by one means or another is... 

Given that the primary source of waterside deposition is almost always hardness salts, good operational practice dictates that (HW heating boilers aside) all boiler plants, wherever located and no matter how limited their output or pressure rating, require softened MU water as a minimum form of pretreatment. 

Although any given source of water typically has a wide range of dissolved minerals present, and each of these has a potential for causing difficulties to a greater or lesser extent, it is the alkaline earth salts (.hardness salts) that are always present to some degree and generally are the most troublesome in a boiler. This section discusses these salts, their presence in natural makeup (MU) water sources, and their contribution to hardness scales and deposition in boiler plants. 

Temporary hardness or carbonate hardness is removed by heating water to precipitate the carbonate salt (e.g., bicarbonate hardness salts) and is equal to or less than the total alkalinity. 

The principal temporary hardness salt in raw water is calcium bicarbonate, formed by dissolution of limestone (calcium carbonate) by... 

Under hot BW conditions this reaction is reversible, leading to a serious risk of carbonate scale depositing on heat transfer surfaces. Consequently, many large water utilities and industries around the world continue to use the old established, but effective lime (calcium hydroxide) and soda ash (sodium carbonate) processes to soften water by precipitating out insoluble hardness salts. 

Both IX units remove hardness salts, and by splitting the RW stream based on incoming water analysis and treated water needs, any level of alkalinity can be produced. As in other dealkalization processes, the treated water TDS is reduced proportional to the alkalinity removed. 

In addition to their poor solubility in water, alkyl phosphate esters and dialkyl phosphate esters are further characterized by sensitivity to water hardness [37]. A review of the preparation, properties, and uses of surface-active anionic phosphate esters prepared by the reactions of alcohols or ethoxylates with tetra-phosphoric acid or P4O10 is given in Ref. 3. The surfactant properties of alkyl phosphates have been investigated [18,186-188]. The critical micelle concentration (CMC) of the monoalkyl ester salts is only moderate see Table 6 ... 

Foamability of phosphoric acid esters in aqueous solutions is in general only moderate, with the acid phosphates showing a better stability against water hardness than the alkali or amine salts. 

Far less than the stoichiometric amount of sequestrants precipitation of insoluble salts from water hardness can be prevented by slowing down the formation of crystals and crystal growth. This process is called the threshold effect. It has long been used in the preparation of boiler feeding water, e.g., steam vessels of railroad engines. Originally sodium pyrophosphate was used for this task, but alkylphosphonic acids and derivatives thereof are superior in their effect. 

In some modern laundry formulations water hardness-promoting ions are bound to aluminosilicates. However, binding of hardness-promoting ions can only take place if these ions are solved in water. Because aluminosilicates or zeoliths are not soluble in water by themselves they are not able to solve insoluble salts of fatty acids already present in incrustations of fibers. For a suf-... 

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