Hard lime

This will produce an, insoluble hard lime soap and a solution of glycenne, the latter of which may be separated by opening the top of the perforated pipe connected with... 

By addition of slaked lime, in calculated quantity for the par ticular degree of hardness (Clark s method) ... 

For temporary hardness due to magnesium carbonate, more lime is required, since the magnesium precipitates as the hydroxide (less soluble than the carbonate) ... 

It is thus important to determine the relative amounts of calcium and magnesium, for addition of too much lime means that calcium ions are reintroduced into the water, i.e. it becomes hard again, the hardness being permanent. 

Hard-burned lime is a quicklime that is calcined at high temperature and is generally characterized by relatively high density and moderate-to-low chemical reactivity. 

Hardness. Most limestone is soft enough to be readily scratched with a knife. Pure calcite is standardized on Mohs scale at 3 aragonite is harder, 3.5—4. Dolomitic limestone is generally harder than high calcium. Dead-burned or sintered limes are 3—4 on this scale, whereas most commercial soft-burned quicklimes are 2—3 (see Hardness). 

Silica and Alumina. The manufacture of Pordand cement is predicated on the reaction of lime with siUca and alumina to form tricalcium sihcate [12168-85-3] and aluminate. However, under certain ambient conditions of compaction with sustained optimum moisture content, lime reacts very slowly to form complex mono- and dicalcium siUcates, ie, cementitious compounds (9,10). If such a moist, compact mixture of lime and siUca is subjected to steam and pressure in an autoclave, the lime—silica reaction is greatiy accelerated, and when sand and aggregate is added, materials of concrete-like hardness are produced. Limestone does not react with siUca and alumina under any circumstances, unless it is first calcined to lime, as in the case of hydrauhc lime or cement manufacture. 

Miscellaneous Kilns. A U.S. kiln, the Fluo-Sohds, appears to be another vertical kiln type, but this is its only similarity. It operates on a different principle. It utilizes as kiln feed only a discrete granulation of 0.225—2.4 mm (65—8 mesh) sizes. DeHcately controlled by air and exhaust gas pressure, the kiln feed of granules is fluidized as a dense suspension. Because it is instmmented, this kiln can produce a very reactive lime at better than average thermal efficiency. The kiln, however, has limited utifity because the cost of obtaining the kiln feed with many hard, compact limestones is prohibitive. 

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). 

Bone, or osseous tissue, is composed of osteocytes and osteoclasts embedded in a calcified matrix. Hard tissue consists of about 50% water and 50% solids. The solids are composed of cartilaginous material hardened with inorganic salts, such as calcium carbonate and phosphate of lime. 

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. 

Amidosulfonates. Amidosulfonates or A/-acyl-A/-alkyltaurates, are derived from taurine, H2NCH2CH2S02Na, and are effective surfactants and lime soap dispersants (Table 9). Because of high raw material cost, usage is relatively small. Technically, amidosulfonates are of interest because they are stable to hydrolysis, unaffected by hard water, and compatible with soap. They have been used in soap—surfactant toilet-bar formulations. With shorter, acyl groups, they make excellent wetting agents. 

Caustic soda is removed from the carbonate—bicarbonate solution by treating with a slight excess of hard-burned quicklime (or slaked lime) at 85—90°C in a stirred reactor. The regenerated caustic soda is separated from the calcium carbonate precipitate (lime mud) by centrifuging or rotary vacuum filtration. The lime mud retains 30—35% Hquid and, to avoid loss of caustic soda, must be weU-washed on the filter or centrifuge. Finally, the recovered caustic solution is adjusted to the 10% level for recycle by the addition of 40% makeup caustic soda. 

Precipitation softening processes are used to reduce raw water hardness, alkalinity, siHca, and other constituents. This helps prepare water for direct use as cooling tower makeup or as a first-stage treatment followed by ion exchange for boiler makeup or process use. The water is treated with lime or a combination of lime and soda ash (carbonate ion). These chemicals react with the hardness and natural alkalinity in the water to form insoluble compounds. The compounds precipitate and are removed from the water by sedimentation and, usually, filtration. Waters with moderate to high hardness and alkalinity concentrations (150—500 ppm as CaCO ) are often treated in this fashion. 

Noncarbonate or permanent calcium hardness, if present, is not affected by treatment with lime alone. If noncarbonate magnesium hardness is present in an amount greater than 70 ppm and an excess hydroxyl alkalinity of about 5 ppm is maintained, the magnesium will be reduced to about 70 ppm, but the calcium will increase in proportion to the magnesium reduction. 

Hot Process Softening. Hot process softening is usually carried out under pressure at temperatures of 108—116°C. At the operating temperature, hot process softening reactions go essentially to completion. This treatment method involves the same reactions described above, except that raw water COg is vented and does not participate in the lime reaction. The use of lime and soda ash permits hardness reduction down to 0.5 g/gal, or... 

Alkalinity Reduction. Treatment by lime precipitation reduces alkalinity. However, if the raw water alkalinity exceeds the total hardness, sodium bicarbonate alkalinity is present. In such cases, it is usually necessary to reduce treated water alkalinity in order to reduce condensate system corrosion or permit increased cycles of concentration. 

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 ... 

The reaction of magnesium noncarbonate hardness with lime and with soda ash is a two step reaction since reaction 6 produces a reasonably soluble calcium salt that must react with in order to cause calcium precipitation ... 

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. 

The needed amounts of lime and soda ash can be calculated from the stoichiometry of the reactions. The effluent quaUty is a function of the solubihties of calcium carbonate and magnesium hydroxide and of the quantities of softening chemicals added. The acceptable level of total hardness can be decided and usually is 70—120 mg/L (265—454 mg/gal), expressed as CaC03. The sum of the solubihties of calcium carbonate and magnesium hydroxide is ca 50—70 mg/L (190—265 mg/gal), depending upon the pH. The sum of the concentrations of the carbonic species HCO/ +, ... 

Calcium Oxide. Also called lime or quicklime (4,5), calcium oxide [1305-78-8] (Class 1, nonregenerative), is relatively iaexpensive. It is prepared by roasting calcium carbonate (limestone) and is available ia a soft and a hard form according to the way ia which it was burned. For desiccant service, soft-burned lime should always be used. Calcium oxide is most commonly used to dehydrate Hquids and is most efficient when it can be heated to speed the reaction rate. The reaction product is calcium hydroxide, which cmmbles as it picks up moisture. 

In a study of the adsorption of soap and several synthetic surfactants on a variety of textile fibers, it was found that cotton and nylon adsorbed less surfactant than wool under comparable conditions (59). Among the various surfactants, the cationic types were adsorbed to the greatest extent, whereas nonionic types were adsorbed least. The adsorption of nonionic surfactants decreased with increasing length of the polyoxyethylene chain. When soaps were adsorbed, the fatty acid and the aLkaU behaved more or less independently just as they did when adsorbed on carbon. The adsorption of sodium oleate by cotton has been shown independently to result in the deposition of acid soap (a composition intermediate between the free fatty acid and the sodium salt), if no heavy-metal ions are present in the system (60). In hard water, the adsorbate has large proportions of lime soap. 

Cyclohexene oxide [286-20-4] M 98.2, b 131-133 /atm, dj 0.971, n 1.452. Fractionated through an efficient column. The main impurity is probably H2O. Dry over MgS04, filler and distil several limes (b 129-134 /aim). The residue is sometimes hard to remove from the distilling flask. To avoid this difficulty, add a small amount of a mixture of ground NaCl and Celite (1 1) to help break the residue particularly if H2O is added. [Org Synth Coll Vol I 185 7945.]... 

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