Calcium carbonate formation

It is surprisingly difficult to calculate whether seawater is supersaturated or undersaturated with respect to CaC03. There are a number of different approaches to the problem all based on equilibrium relationships that describe the precipitation 

Seawater is a concentrated and complex solution in which the ions are close together, compared with those in a more dilute solution. Electrostatic interaction occurs between closely neighbouring ions and this renders some of these ions inactive . We are interested in the available or active ions and we correct for this effect, using activity coefficients, denoted y (see Section 2.6). 

Activity coefficients are notoriously difficult to measure in complex solutions like seawater, but are thought to be around 0.26 for Ca2+ and around 0.20 for car- 

IAP = Ca2+ x aCOl- = cCa2+ y x cC02f y = 0.01x0.26x0.00029x0.2 

This value is much greater than the solubility product (see Box 4.12) of calcite (CaC03), which is 3.3 X 10-9mol21-2 at 25°C and 1 atmosphere pressure, a suitable choice for tropical surface seawater. The degree of saturation (see Box 4.12) is  

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Separation-layer micro mixers are specially tools for mixing solutions which react fast or tend to foul otherwise [39, 53, 135-138], The most prominent example of such processes is probably the generation of particles by immediate precipitation, as e.g. for calcium carbonate formation. Separation-layer mixers thus overcome the limits of normal micro mixers, which tend to clog under such conditions. 

M 54] [P 48] Separation-layer micro mixers with concentric multi-layered outlets can be operated in a droplet-forming mode [53] If fast precipitating solutions are contacted in this way with a solvent layer for initial separation, the part of the droplet close to the tube outlets remains transparent, which demonstrates that a tri-layered system still exists with the two reacting solutions not being intermixed, as evidenced by calcium carbonate formation in aqueous solutions as described in [39,136], At the droplet end cap the layers collide and circulation flow sets in. As a result, mixing is achieved and precipitation occurs. The circulation patterns are visualized by the particle trajectories. 

Table 2.2. Typical parameter values for calcium sulfonates, alkylphenyl sulfides and alkylsalicylates detergents with additional total base number (TBN, mgKOH/g oil) from calcium carbonate. Formation of hard-core reverse micelles (RMs) of calcium carbonate-sulfonate or alkylphenate and soft-core revere micelles (RMs) of calcium alkylsalicylate in oil formulations...

In the present ocean calcium carbonate formation is dominated by pelagic plants (coccolithophores) and animals (foraminifera, pteropods, and heteropods). Examples are presented in Figure 4.13. Although benthic organisms are important in shoal water sediments, and for dating and geochemical studies in the deep sea sediments, they constitute only a minor portion of the calcium carbonate removed from deep seawater. Shoal water carbonates are discussed in detail in Chapter 5. 

Extracellular calcium carbonate formation by some cyanobacteria and algae, which are photo synthetic autotrophs that obtain their carbon from CO2, can be explained by Eq. (1.5) above. In that instance, the uptake and fixation of CO2 by the cyanobacteria and algae promotes C03 formation needed for precipitation of extracellular CaC03. In the cyanobacterium Synechococcus, the Ca precipitated by C03 from photosynthesis is derived from that bound to the cell surface of Synechococcus (Thompson et al., 1990). 

Reddy, M.M., and Nancollas, G.H. Calcite crystal growth inhibition by phosphonates. Desalination 12, 61-73 (1973). Reddy, M.M., Kinetics of calcium carbonate formation. Proc. Internat. Assoc. Theoret. Appl. 

Reddy, M.M. Kinetic inhibition of calcium carbonate formation by wastewater constituents, p. 31-56, in Rubin, A.J., ed., "Chemistry of Wastewater Technology/ Ann Arbor Science,... 

Sediment phosphorus extraction analyses show that hydrous iron oxides (extracted by (NH4)2C204) play a major role in the transport of sediment phosphorus. In northern areas of the Genesee River watershed calcium carbonate formation also appears to be Involved in phosphorus fixation. Ion activity product calculations for water column samples from the Genesee River consistently exhibit subsaturation with respect to the stable calcium phosphate phase, hydroxyapatite. Calcium carbonate, which can serve as a substrate for phosphate mineralization, shows an ion activity product below the solubility product in the Genesee River except during the summer low-rainfall season. 

The term anaerobic respiration describes oxidation of organic matter by inorganic electron acceptor other than O. Two of the most important inorganic electron acceptors are nitrate and sulfate and their reduction may be accompanied by calcium carbonate formation. In nitrate reduction (denitrification) by heterotrophs, either N2 or N2O are formed and the overall reduction-calcification processes are expressed by eqns (7) and (8) where C represents organic carbon ... 

Although calcium carbonate formation in soil is a result of high evapotranspiration rates relative to precipitation rates, the term evaporite is usually restricted to compounds more soluble than CaCC>3. Where drainage water from surrounding soils accumulates and where the amount of percolated water is small compared to the amount of water evaporated, soluble salts tend to accumulate. This subject is dealt with in more detail in Chapter 11. The present section is restricted to the extreme case of natural salt flats and play as (former and intermittent lake beds). 

The polar nature of the catalytic decomposition of cumene hydroperoxide with added terf-butyl terf-butanethiolsulfinate has been clearly established (I). The thiolsulfinate is converted into an active peroxide decomposer capable of destroying many moles of hydroperoxide per mole of sulfur compound. The acidic character of the active species was demonstrated by its effective neutralization with the added base calcium carbonate. Formation of the active peroxide decomposer may be envisaged as involving one or more of the following three reaction types concerted process, ionic processes, and free-radical processes. 

The green color suggests chromium or copper but the blue solution formed when the mineral is dissolved in sulfuric acid points to copper as the metal (CuSO is blue). The colorless gas that forms either upon heating or on treatment with acid is carbon dioxide this is proven when the gas is bubbled into limevvater (the cloudiness in the solution is due to calcium carbonate formation). CO, is formed when carbonates are either heated... 

Carbonic acid formation decreases local pore solution pH from 14 to 8. This fall initiates passive hydrated ferric oxide film destruction and hydrated calcium carbonate formation ... 

In this reaction, the calcium ions and bicarbonate are combined in an aqueous medium to form calcium carbonate, which is slightly soluble in water. The calcium carbonate formation in surface waters and its precipitation into the oceanic floor is important in the transference of carbon from surface to deep water [49]. 

Crystallization of calciiun carbonate is highly dependent on precipitation conditions. In the classical method, much of the scientific investigation of calcium carbonate formation focused on the seed growth of anhydrous calcite crystals from solutions of low supersaturation [23-26]. A crystal can precipitate via epitaxy directly from the liquid solution so that the nuclei bear the same structure as the final crystal. 

These shells both protect the crayfish and store. .. A. Sato et al. Glycolytic intermediates induce amorphous calcium carbonate formation in crustaceans. 2011. NatChem Biol. 7(4), p. 197. DOl 10.1038/nchembio.532. 

RSI > 7 the calcium carbonate formation probably does not lead to a protective corrosion inhibitor film... 

Calcium carbonate formation is accompanied by a decrease in the water content and increase in the weight of concrete, thus causing the cracking of the surface. Carbonation shrinkage decreases the cover to reinforcement and increases the risk of ingress of corrosive species. Most important however, is the fall in pH as the concrete becomes less... 

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