Computer Science
Scientific paper
Mar 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991gecoa..55..659s&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 55, Issue 3, pp.659-669
Computer Science
5
Scientific paper
The solubility of portlandite was measured in H 2 O and aqueous acetate solutions of varying concentration (1-10 mmolal) at temperatures from 100-350°C and 500 bars pressure. Dissolved Ca concentrations increased with decreasing temperature and increasing dissolved acetate concentration. Using known thermodynamic data for portlandite, H + , OH - , Ca ++ , CH 3 COO - , CH 3 COOH 0 , and H 2 O (1) , stability constants for CaOH + and CaCH 3 COO + complexes were determined. Log K values for the reaction Ca ++ + H 2 O (1) = CaOH + + H + are, respectively, -10.04, -8.20, -6.88, and -6.35 at 100, 200, 300, and 350°C and 500 bars pressure and for the reaction CaCH 3 COO + = Ca ++ + CH 3 COO - are, respectively, -2.53, -3.72, -4.59 at 200, 300, and 350°C and 500 bars pressure. These results indicate that the stabilities of CaOH + and CaCH 3 COO + complex increase with increasing temperature. In the acetate-free experiments, CaOH + is the dominant form of dissolved Ca in equilibrium with portlandite at 100-350°C and 500 bars, while in the acetate-rich experiments (10 mmolal acetate), Ca ++ and CaOH + are the dominant forms of Ca in equilibrium with portlandite at low temperature (100-200°C) and CaCH 3 COO + and CaOH + are the dominant forms at relatively high temperature (200-350°C). Metal-acetate complexing has long been suggested as an important mechanism for mobilizing base metals during the formation of ore deposits in organic-rich environments. Due to the stability of CaCH 3 COO + complex in Ca-bearing fluids at elevated temperatures and pressures, however, the effectiveness of dissolved acetate to enhance base metal sulfide solubility is limited.
Seewald Jeffrey S.
Seyfried William E. Jr.
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