Calcium carbonate CaCO precipitation

A big concern in swimming pools is prevention of etching and scaling (ie, precipitation of CaCO ) which can be controlled by maintenance of a proper degree of saturation with respect to calcium carbonate. The calcium carbonate dissolution-precipitation equiUbrium is represented by ... 

Calcium carbonate [471-34-1]—Cl Pigment White 18, Cl No. 77220, EEC No. E 170. A fine, white, synthetically prepared powder consisting essentially of precipitated calcium carbonate, CaCO. ... 

Permanent hardness can also be due to the presence of CaS04, in which case the addition of soda (sodium carbonate), NaiC03, produces sodium sulfate, Na2S04, and calcium carbonate, CaCO, this precipitate once again is removed by sedimentation. 

The fact that protons are used as a motive force can contribute to an increase in the pH of the soil solution, due to the uptake by bacteria. Moreover, the pH can also be increased due to the fact that reactions involve the transformation of oxalic acid into carbonic acid, i.e. of a strong (pKi = 1.25, pK2 = 4.27) to a weak (pKi = 6.35, pK2= 10.33) acid (Braissant et al., 2002). This alkalinization facilitates precipitation of calcium carbonate (CaCOs). By modifying a general equation for oxalate metabolism by oxalatrophic bacteria (Harder et al., 1974), the following balanced equation can be proposed ... 

All these results are related to observations and measurements in the field as well as from oxalotrophic bacterial cultures in the laboratory (Braissant et al, 2004). There is no theoretical model available to explain the oxalate-carbonate transformation and its consequences on the soil solution properties, i.e. alkalinization facilitating precipitation of calcium carbonate (CaCOs) and CO2 release into the atmosphere. This kind of model should be able to explain the process of oxido-reduction reactions, pH regulation and the evolution of the various phase concentrations involved in the system, i.e. oxalate, carbonate, water and CO2. This is the aim of the next section. 

For the raw water of Example 10.8, using the lime-soda process in the spht treatment mode to remove the total hardness to 130 mg/L as CaC03 containing magnesium hardness of 40 mg/L as CaCO, calculate the total mass of calcium carbonate solids precipitated from the removal of the magnesium bicarbonate of the carbonate hardness of magnesium. 

The best reagent for selective reduction of alkynes to the cis alkene is the Lindlar catalyst.3 1 Palladium chloride (PdCl2) was precipitated on calcium carbonate (CaCOs) in acidic media and deactivated with lead tetraacetate [Pb(OAc)4] to give the named Pd-CaC03-Pb0 catalyst. Reduction of alkynes will stop at the cis alkene with little or no cis-trans isomerization. A variation uses quinoline as a poison, and this catalyst was used by Overman and co-workers to convert alkyne 378 to cis-alkene 379 as part of a synthesis of... 

Reinforcing fillers (active) Fumed Silica (Si02) precipitated calcium carbonate (CaCOs) carbon black Thixotropic reinforcing agents (non-slump), adjustment of mechanical properties (cohesion) provide toughness to the elastomer as opposed to brittle materials. 

The two parameters that control corrosivity of soft waters are the pH and the dissolved oxygen concentration. In hard waters, however, the natural deposition on the metal surface of a thin diffusion-barrier film composed largely of calcium carbonate (CaCOs) protects the underlying metal. This film retards diffusion of dissolved oxygen to cathodic areas, supplementing the natural corrosion barrier of Fe(OH)2 mentioned earlier (Section 7.2.3). In soft water, no such protective film of CaCOs can form. But hardness alone is not the only factor that determines whether a protective film is possible. Ability of CaCOs to precipitate on the metal surface also depends on total acidity or alkalinity, pH, and concentration of dissolved solids in the water. For given values of hardness, alkalinity, and total dissolved salt concentration, a value of pH, given the symbol pHs, exists at which the water is in equilibrium with solid CaCOs. When pH > pHs, the deposition of CaCOs is thermodynamically possible. 

Precipitation reactions are important in industry, medicine, and everyday life. For example, the preparation of many essential industrial chanicals such as sodium carbonate (NajCOs) is based on precipitation reactions. The dissolving of tooth enamel, which is mainly made of hydroxyapatite [Ca5(P04)30H], in an acidic medium leads to tooth decay. Barium sulfate (BaS04), an insoluble compound that is opaque to X rays, is used to diagnose ailments of the digestive tract. Stalactites and stalagmites, which consist of calcium carbonate (CaCOs), are produced by a precipitation reaction, and so are many foods, such as fudge. 

Flue-Gas (Stack-Gas) Scrubbing. Flue-gas scrubbing is a refiner s last chance to keep NOx and SOx out of the air. In wet flue-gas desulfurization, gas streams containing SOx react with an aqueous slurry containing calcium hydroxide Ca(OH)2 and calcium carbonate CaCOs. Reaction products include calcium sulfite (CaSOs) and calcium sulfate (CaS04>, which precipitate from the solution. 

Langelier index A calculated number used to predict the calcium carbonate (CaCOs) stability of a water that is, whether a water will precipitate, dissolve, or be in equilibrium with calcium carbonate. It is sometimes erroneously assumed that any water that tends to dissolve calcium carbonate will always be corrosive. 

Determine the calcium ion concentration that a shell-forming organ must locally maintain to precipitate calcium carbonate (CaCOs) under two conditions of equilibrium a preindustrial atmosphere containing approximately 280 ppm CO2 or a modem atmosphere containing approximately 400 ppm C02- To address this question, the [Ca ] in water that has equilibrated with both solid CaCOs and with the specified atmospheres must be calculated. A value of [Ca ] higher than the calculated equilibrium value will tend to enable CaCOs precipitation, while values lower than the calculated equilibrium value will prevent precipitation and will tend to promote dissolution. 

Abrasive powders in a paste or fluid carrier - e.g. SiC, AI2O3, diamond, precipitated calcium carbonate (CaCOs), CeO, talc, kaolin, wheat starch, and Snow-Floss ... 

Precipitated Calcium Carbonate. Calcium carbonate [471-34-1] (Turns), CaCO, is a fine white microcrystaUine powder without odor or taste. It is stable in air. An aqueous suspension is close to neutrality. It is practically insoluble in water, insoluble in alcohol, and dissolves with effervescence in dilute acetic, hydrochloric, and nitric acids (see Calcium compounds, calcium carbonate). 

Aragonite. Calcium carbonate is a common deposit in shallow tropical waters as a constituent of muds, or in the upper part of coral reefs where it precipitates from carbon dioxide-rich waters supersaturated with carbonate from intense biological photosynthesis and solar heating. Deposits of ooHtic aragonite, CaCO, extending over 250,000 km in water less than 5 m deep ate mined for industrial purposes in the Bahamas for export to the United States (19). 

Phosphate and phosphonate molecules have a very high affinity for calcium carbonate surfaces, as shown by their influence on the precipitation and growth of calcite [164-166]. Accordingly, organophosphorus compounds such as alkylphosphoric acids [167-169] and phosphonic acid-terminated polyoxyethylene [170, 171] have been used to modify the surface of CaCOs powders. 

Distinguishing between calcium carbonate precipitates adjacent to actively metabolizing cyanobacteria versus cell directed mineralization, i.e., via bioorganic molecular templates, is often moot. It is probable that both processes take place intermittently if not sequentially with shifts in temperature and composition, alkalinity or salinity, of the surrounding fluid media, especially when the waters are effectively saturated with respect to carbonate and calcium ions. Where the waters are in rapid motion, as in springs and waterfalls, CaCOs deposition may be aided by evaporation while bioprecipitation of carbonates is also taking place (Golubic, 1973, 1983). 

The rate of global production of bicarbonate by weathering can be determined because we loiow approximately the flow of HCO J in the world s major rivers. This represents a drain of the CO2 of the atmosphere, which must be balanced by resupply to maintain a steady One is tempted to estimate the vulnerability of atmospheric/co to the imbalance between the atmospheric CO2 drain by weathering and resupply by CaCOs precipitation by focusing on the CO2 fluxes from and to the atmosphere. This, however, would be incorrect because the ocean and atmosphere carbon reservoirs are approximately in chemical equilibrium on time scales greater than the circulation of the ocean (see Chapter 11). In order to emphasize the severity of the HCOs imbalance estimated in Fig. 2.4 one should focus on the fluxes of DlC and alkalinity between the land and ocean. Because we have not yet discussed alkalinity and DIC relationships (Chapter 4) a simple approximation can be made by considering the fluxes of bicarbonate and calcium. 

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