Calcite acetic acid effect

Table V. Effect of Acetic Acid Addition on Calcite Solubility. Modeled with...

Figure 8. Results of a geochemical model investigating the effects of pH buffering by acetic acid-acetate on the response of the carbonate system to changes in pCO. Increases in the pC02 of calcite-saturated solutions will promote calcite undersaturation for initial concentrations of acetic acid up to approximately 0.06 m (3600 mg/I). This is called the crossover concentration. (Reproduced with permission from Ref. 7. Copyright 1989 Elsevier).

They also reacted andesine with 1000 ppm oxalate solutions (buffered with sodium acetate + acetic acid to pH 3.2, 4, 5, and 6). Andesine experiments with 1000 ppm oxalate (10 000 ppm acetate, various pH) showed that the amount of Al and Si02 in the reacted solutions varied inversely with pH at essentially constant oxalate. Similar pH-buffered experiments were conducted with laumontite ( calcite) to determine the effects of calcite on the aluminum content of the fluid. In the absence of calcite, aluminum concentrations in solution were high at low pH (up to 26 ppm at pH 5) but 1 ppm at pH 8 however, when calcite was added to the system, oxalate was removed during the reaction, especially at low pH, and aluminum was below the detection limit. 

Fig. 10. Effect of increasing pC02 on the stability of calcite in the presence of acetic acid. As the acetic acid concentration increases, the buffering capacity of the water increases with respect to the water s ability to consume protons and resist pH change. Thus, at a critical acetic acid concentration (about 0.07 mol 1 4200mgkg ) increases in acidity caused by dissolving CO2 in the water can be offset by the consumption of by the acetic acid-acetate reaction. At lower acetic acid concentrations calcite dissolves, whereas at higher aceteic acid concnetrations calcite may precipitate (Lundegard and Land 1989). Solid symbols are data from Thyne (1992) as shown in Fig. 11. Discrepant predictions between the two studies at the lower acid concentration can be reconciled by a higher concentration of cation-acid anion complexes in Thyne s study. These complexes release cations that cause carbonate mineral precipitiation. The absolute amount of solid formation cannot be calculated from Thyne s data...

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