Carbonate hardness

The lime or lime—soda process results in the precipitation of calcium as calcium carbonate and magnesium as magnesium hydroxide. The solubiUties of these compounds are shown in Figure 4 as functions of pH. When lime is used alone, only the carbonate hardness is reduced. The carbonate hardness is present as calcium or magnesium bicarbonate. The additional use of soda ash can reduce the noncarbonate hardness by providing additional carbonate ion. The reactions involved in the various steps of the process are Hsted below ... 

The reaction of calcium carbonate hardness with lime, when the calcium can be represented as the bicarbonate at the usual pH values ... 

The reaction of magnesium carbonate hardness with lime ... 

From reactions 2—6, it can be seen that the addition of lime always serves three purposes and may serve a fourth. It removes, in order, COg, calcium carbonate hardness, and magnesium carbonate hardness (reactions 8, 9, and 10, respectively). Where magnesium noncarbonate hardness must be removed, the lime converts it to calcium noncarbonate hardness (reaction 6). Soda ash, then, removes noncarbonate hardness according to reaction 5. 

Many analyses quote total hardness. Some give temporary hardness (or carbonate hardness) and permanent hardness (or non-carbonate hardness), usually in consistent units so that the values can be added together to give the total hardness. The total hardness is actually the quantity of calcium (Ca) - - magnesium (Mg) in the water. If the total is not given directly, the values given for these two constituents must be added, after conversion to mg/1 as CaC03 if necessary. 

Temporary or carbonate hardness and alkalinity frequently, but not always, mean the same thing (see below). Bicarbonate or hydrogen carbonate is a more scientific term since alkalinity is actually the concentration of the bicarbonate (HCO3") ion in the water. 

Dezincification of brasses This may occur, particularly in stagnant or slowly-moving warm or hot waters relatively high in chloride and containing little carbonate hardness. Dezincification of a brasses is inhibited by the usual arsenic addition (see Fig. 4.12), but two-phase brasses are liable to severe attack in some waters . In such waters the use of duplex-structure brass fittings should be avoided. 

There are many kinds of carbon materials, with different crystallinity. Their crystallinity generally develops due to heat-treatment in a gas atmosphere ("soft" carbon). However, there are some kinds of carbon ("hard" carbon) in which it is difficult to develop this cristallinity by the heat-treatment method. Both kinds of carbon materials are used as the negative electrode for lithium-ion batteries. 

Acid, 32% Hydrochloric Carbon Rubber Carbon Hard Stainless Steel Carbon Steel Carbon Rubber or Ring Rubber Carbon Rubber ... 

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. 

Primarily the sum of Ca and Mg salts in water, although it may include other metal salts such as Al, Mn, Sr, and Zn. Temporary hardness (carbonate hardness) is that portion of the total hardness that can combine with C03 or HC03. The balance is non-carbonate or permanent hardness and is caused by Ca or Mg nitrates/sul-fates/chlorides, etc. Permanent hardness is equivalent to the excess of hardness over alkalinity. 

Temper heat treatment of metals Temporary Hardness see Carbonate hardness... 

Hardness can also be reduced with a lime-soda ash treatment. This process involves the addition of slaked lime (calcium hydroxide Ca(OH)2), to a hard water supply to convert the hydrogen carbonate hardness to carbonate, which then precipitates and can be removed by filtration ... 

Carbonate Hardness. This is the presence of calcium (Ca) and magnesium (Mg) carbonate and bicarbonate. 

Temporary Hardness. This is the presence of Ca and Mg bicarbonate and can be eliminated by boiling the water to transform bicarbonate into insoluble carbonate. Temporary hardness is slightly different from carbonate hardness because it does not take into account the presence of carbonate, which is only slightly soluble,... 

It is interesting to note that when the total alkalinity is less than the total hardness, then calcium and magnesium are present in compounds other than carbonates, bicarbonates and hydrates. In this case, the amount of hardness equivalent to total alkalinity is the carbonate hardness the remainder is the noncarbonate hardness. 

When the number of concentrations of the circulating water is in the order of 3-7, some of the salts dissolved can exceed their solubility limits and precipitate, causing scale formation in pipes and coolers. The purpose of the treatment of the cooling water is to avoid scale formation. This is achieved by the injection of sulfuric acid to convert Ca and Mg carbonates (carbonate hardness) into more soluble sulfates. The amount of acid used must be limited to maintain some residual alkalinity in the system. If the system pH is reduced to far below 7.0, it would result in an accelerated corrosion within the system. As stated earlier, scale formation and/or corrosion tendency is defined by the Saturation Index (Langelier Index) and Stability Index (Ryznar equation). 

The reaction of alkyl isothiocyanates, RNCS, with diphenylphosphinic hydrazide (338) in benzene has been reported.308 The bis(diethylamino)[(methylthio)thiocarbon-yl]carbenium salts (339 X = I or BF4) display ambident reactivity and can react either at carbenium carbon (hard nucleophiles) or at the thiocarbonyl sulfur atom (soft nucleophiles).309 Electrochemically generated superoxide reacts with dithioic S,S -diesters (dicarbothiolates) (340 Ar = C5H3N or C6H4) to give the monocarboxylate anions in 100% yield before giving the dicarboxylate anions.310... 

The fundamental reason for using lime-soda softening processes is to reduce the temporary hardness (carbonate hardness) content of the raw water in order to minimize risks of carbonate scaling in the user s cooling systems. Often some of the permanent hardness (noncarbonate hardness) is also removed, as is some silica. The principal temporary hardness salt is calcium bicarbonate, formed by dissolution of limestone (calcium carbonate) by water containing dissolved carbon dioxide. 

Hardness of a water sample is a measure of its capacity to precipitate soap. The presence of calcium and magnesium ions in water essentially contributes to its hardness. Other polyvalent ions, such as aluminum, also cause hardness. Their effect, however, is minimal, because these polyvalent ions occur in water often in complex forms and not as free ions. As a result, they cannot precipitate soap. Although calcium is not the only cation causing hardness, for the sake of convenience, hardness is expressed as mg CaC03/L. Similarly, anions other than carbonate, such as bicarbonate, also cause hardness in water. To distinguish the contributions of such anions from carbonates, hardness is sometimes termed as carbonate hardness and noncarbonate hardness. This can be determined from alkalinity. The relationship is as follows ... 

Carbonate hardness = carbonate alkalinity + bicarbonate alkalinity... 

Noncaibonate hardness = total hardness - carbonate hardness... 

When total hardness is equal to or less than the sum of carbonate and bicarbonate alkalinity, all hardness is noncarbonate hardness only and there is no carbonate hardness. 

Kodama and co-workers [58] have reported TG-DSC curves for the analysis of the interaction between vulcanisation accelerators (tetramethylthiuram disulphide, dibenzothiazolyl disulphide, diphenylguanidine and N-cyclohexyl-2-benzothiazolyl-sulphenamide) and fillers (carbon black, white carbon, hard clay and CaC03). The initial melting point (MP) of the accelerators was largely influenced by the fillers. The higher the surface activity of the filler is, the lower and wider the melting range becomes. 

Hard nucleophiles tend to react at the carbonyl carbon (hard) of an enone... 

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