Calcite precipitations

The first alternative is unlikely but not impossible. Past experience suggests that KdSr probably depends on the degree of supersaturation of the solutions with respect to calcite during calcite precipitation (Katz et al., 1972). In the experiments by Shikazono and Holland (1983), the solutions from which anhydrite was deposited were considerably supersaturated. It is therefore possible that the values of K sr extracted from their experimental data are higher than those which controlled the incorporation of Sr in anhydrite during the formation of Kuroko deposits. Experiments at very low degrees of anhydrite supersaturation are needed to determine whether this is a possible explanation for the low Sr content of some of the Kuroko anhydrites. 

In the reaction path we calculated (Fig. 24.2), the precipitation of calcite consumes nearly all of the calcium originally in solution so that no further calciumbearing minerals form. Calcite precipitation, on the other hand, does not deplete... 

If the fluid had been initially richer in calcium than carbonate (MCa++ > MhcOj )> 38 noted by Hardie and Eugster (1970), it would have followed a distinct reaction path. In such a case, calcite precipitation would deplete the fluid in carbonate, allowing the calcium concentration to increase until gypsum (CaS04 2H2O) saturates and forms. The point at which the calcium and carbonate are present at equal initial concentration (MCa++ = Mhco3 ) is known as a chemical divide. 

Application of calcite precipitation rate in predicting the utilization period of calcite scale affected wells, Philippines... 

The utilization periods for AP01D given by the direct deposition of the excess calcite method has a minimum of 1 month and maximum of 6 months as shown in Fig. 2. It should be noted that the calcite precipitation rate equation at a saturation ratio above 1.72 provided shorter utilization time than the direct deposition method, indicating that the rate law overestimated the amount of calcite deposited. At a saturation ratio below 1.72, however, the rate law indicated a longer utilization period, which was expected since the calcite deposition is kinetically controlled rather than instantaneous deposition of the excess calcite. 

The calcite precipitation rate (Eq. 1) should be further refined by calibrating the equation to the field condition particularly for saturation ratio above 1.72. 

Shiraki, R. Brantley, S.L. 1995. Kinetics of near-equilibrium calcite precipitation at 100°C An evaluation of elementary reaction-based and affinity-based rate laws. Geochemica et Cosmochimica Acta, 59, 1457-1471. 

Geochemical monitoring of chemical and isotopic compositions of CO2 fluids and calcite precipitation during injection tests at Ogachi Hot-Dry Rock site, Japan... 

Figure 7.15 A simple ocean-atmosphere-continent system. Pressure of C02 enhances Ca release from the continental crust (which is assumed to be made of CaSi03) and controls the depth of calcite saturation. Calcite precipitation is therefore controlled by the hypsometric curve, equation (7.4.8), and Pco2-...

Broecker and Takahashi, 1978). zs is the depth in km and carbonate concentrations are in mol kg" . Since seawater Ca2+ concentration is allowed to change as a result of calcite precipitation and river input, it is more general to state that the saturation product Ks changes as... 

Figure 7.17 Same as Figure 7.16 for pCOl, seawater alkalinity A, runoff [Ca2+] and the fraction F of precipitated calcite which is preserved on the ocean floor. It takes a little less than 10000 years for runoff calcium to neutralize the excess dissolved COz, but calcite precipitation takes much longer to eliminate Ca and carbonate excess. 

Experimental and empirical studies have demonstrated that certain doubly charged cations of ionic radius less than calcium (e.g., Mn2 +, Zn2+, Fe2+, Cd2 +, and Co 2+) can be extensively incorporated into calcite precipitated from aqueous solution at... 

Prior to the advent of the coccolithophorids and planktonic foraminferans, 200 to 250 miUion years ago, all biogenic calcite precipitation must have been restricted to the shallow waters of the neritic zone. Thus, the evolution of the pelagic calcifiers ushered... 

Inskeep and Bloom (1986) measured inhibition of calcite precipitation by organic ligands in simulated soil solutions prepared from CaCl2,KHC03 and seeds of CaCOs, and maintained at constant pH and CO2 pressure. The data fitted the rate equation ... 

However, rates of precipitation in soil systems may be quite different from those in solutions because precipitation is catalysed by adsorption of the reacting solutes onto soil surfaces the nature of the solid phases formed may be different and sorption may also alter the effects of inhibitors. There are very few data in the literature on these effects actually measured in soils. Figure 3.15 shows data of Huang (1990) for calcite precipitation in three soils incubated with urea. Precipitation was induced as the pH increased during urea hydrolysis ... 

Figure 3.16 Inhibition of calcite precipitation by P and water-solnble organic matter calcnlated with Eqnation (3.54) derived nsing the data in Fignre 3.15. Nnmbers on cnrves are concentrations of P and DOC in the soil solution (mM)...

Inskeep WP, Bloom PR. 1986. Kinetics of calcite precipitation in the presence of water-soluble organic ligands. Soil Science Society of America Journal 50 1167-1172. 

Palmer AN (1996) Rates of limestone dissolution and calcite precipitation in cave streams of east-central New York state, northern section. Geol Soc Am 28 89 Parker BL, Cherry JA, Chapman SW, Guilbeault MA (2003) Review and analysis of chlorinated solvent dense nonaqueous phase liquid distribution in five sandy aquifers. Vadose Zone J 2 116-137... 

Plotting a variable that is significant when small is rather difficult. The method developed to clearly highlight the areas of calcite precipitation on a chart or plan map involves some manipulation. To do this, the acidified H" in moles (converted from pH) is subtracted from the non-acidified H". The least differences are the areas of calcite precipitation. The inverse difference (1/difference) is calculated and plotted. This variable produces positive peaks which are far more pleasing to the eye. For ease these are called Inverse Difference Hydrogen (IDH) anomalies. 

Figure 3.12 presents 5 C and 5 0-values of hydrothermal carbonates from the Pb-Zn deposits of Bad Grund and Lautenthal, Germany. The positive correlation between and 0/ 0-ratios can be explained either by calcite precipitation... 

Studies of the sorption of natural radionuclides from groundwater have established that minor minerals, such as clays coating the fractures in crystalline rock and Fe- and Mn-oxyhydroxides, are important sinks for radionuclides. For example, investigations carried out at the Aspo facility (Smellie Karlsson 1999) showed qualitatively that rare earth elements (REEs), Sc, Th, U, Ra, and Ba have been scavenged by Fe-oxyhydroxide and calcite precipitates,... 

Heavy metal cations precipitate readily as hydroxides or carbonates in alkaline media. Dissolved carbonate content will be limited by calcite precipitation or by conversion of hydroxyl AFm to carbonate AFm. Hydroxide ions, on the other hand, are abundant. Here only the solids that may be present under oxic conditions will be discussed. Figure 5a shows the total dissolved heavy metal cation concentrations that would prevail if hydroxide precipitation were to be the dominant solubility-controlling process. Figure 5b shows the solubility of Ca metallate species, as these are likely to act as solubility-controlling phases for oxyanionic species. 

Calcium carbonate precipitation and sedimentation from mid-August through October (ref. 20 see also the following discussion of components) significantly enhanced P fluxes. The impact of calcite precipitation on P removal from the epilimnion is shown in Figure 8. Phosphorus flux into the... 

The general equation for weathering (to the right) and calcite precipitation (to the left) in soils is ... 

Figure 3.1. MgC03 content of precipitated magnesian calcites as a function of the Mg to Ca molar ratio in solution. (+) Berner (1975), pH-stat experiments (a) Mucci and Morse (1983), pH-stat ( ) Kitano and Kanamori (1966), free drift ( )Glover and Sippel (1967), free drift (O) Katz (1973), free drift ( ) McCauley and Roy (1974), free drift (O) Devery and Ehlmann (1981), free drift ( )Last (1982), composition of magnesian calcites precipitating in water column, Lake Manitoba, Canada. (After Mackenzie et al., 1983.)...

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