Calcite precipitation solutions

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... 

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... 

Dreybrodt W, Buhmann D. A mass transfer model for dissolution and precipitation of calcite from solutions in turbulent motion. Chem Geol 1991 107-122. 

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)...

At the higher saturation state, the seawater solution is more than 5 times supersaturated with respect to aragonite so that aragonite would be expected to precipitate on the aragonite seed crystal. Results indicated that Mg2+ is adsorbed between 25 to 40 times less on aragonite than on calcite from solutions supersaturated with respect to both minerals. 

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.)...

The transformation of aragonite to calcite can be catalyzed in solutions containing electrolytes which are not inhibitors of calcite precipitation (e.g., NaCl). This observation has been interpreted to be due to increased concentrations of the calcium bicarbonate ion pair (e.g., Bischoff and Fyfe, 1968) in these solutions. Why this species should catalyze the reaction remains unexplained. 

Figure 7.20. Trends in calcite precipitation rates on calcite seeds in different aqueous solutions at 25°C and a Pc02 °f 10 2-5 atm. as a function of calcite saturation state. Solution compositions are indicated on the diagram. (Data from Reddy et al., 1981 Mucci and Morse, 1983 Walter 1986.)...

Figure 7.21. A) Relative rates of calcite and aragonite precipitation in solutions with Mg Ca =1. B) Relative rates of calcite and aragonite precipitation in solutions with Ca Mg = 1 and containing dissolved sulfate. Note that in solutions without sulfate calcite precipitates faster, whereas in solutions containing sulfate aragonite precipitates faster. (After Walter, 1986.)...

Fig. 50 Calcite solubility and incongruent solution calcite-dolomite (calcite -precipitation and dolomite dissolution)...

We have studied the dissolution kinetics of calcite in stirred CO2 water systems at CO2 partial pressures between 0.0003 and 0.97 atm and between 5° and 60°C, using pH-stat and free drift methods (J ) Our results suggest a mechanistic model for reactions at the calcite-aqueous solution interface that has broad implications to the controls on calcite dissolution and precipitation under diverse chemical and hydrodynamic conditions. 

Dreybrodt, W., 1981, The kinetics of calcite precipitation from thin films of calcareous solutions and the growth of speleothems Revisited, Chem. Geol. 32 237-245. 

STM of galena and surface oxidation and sorption of aqueous gold were reported in a recent study. The calcite precipitation mechanisms were investigated by AFM. The crystals of proteins are difficult to obtain but are prerequisite for any kind of electron microscopic analysis. Because all protein molecules are composed primarily of 25 different amino acids, it was useful to determine the crystal structure of each amino acid by AFM. A solution of amino acid of concentration... 

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