Experimental determination of portlandite solubility in H sub 2 O and acetate solutions at 100-350C and 500 bars: Constraints on calcium hydroxide and calcium acetate complex stability

Journal Article · Fri Mar 01 04:00:00 EST 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90331-X· OSTI ID:6038861

Seewald, J S; Seyfried, Jr, W E ^[1]

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1. Univ. of Minnesota, Minneapolis (United States)

The solubility of portlandite was measured in H{sub 2}O and aqueous acetate solutions of varying concentration (1-10 mmolal) at temperatures from 100-350C and 500 bars pressure. Dissolved Ca concentrations increased with decreasing temperature and increasing dissolved acetate concentration. Using known thermodynamic data for portlandite, H{sup +}, OH{sup {minus}}, Ca{sup ++}, CH{sub 3}COO{sup {minus}}, CH{sub 3}COOH{sup 0}, and H{sub 2}O{sub (1)}, stability constants for CaOH{sup +} and CaCH{sub 3}COO{sup +} complexes were determined. These results indicate that the stabilities of CaOH{sup 1} and CaCH{sub 3}COO{sup 1} complex increase with increasing temperature. In the acetate-free experiments, CaOH{sup +} is the dominant form of dissolved Ca in equilibrium with portlandite at 100-350C and 500 bars, while in the acetate-rich experiments (10 mmolal acetate), Ca{sup ++} and CaOH{sup +} are the dominant forms of Ca in equilibrium with portlandite at low temperature (100-200C) and CaCH{sub 3}COO{sup +} and CaOH{sup +} are the dominant forms at relatively high temperature (200-350C). 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{sub 3}COO{sup +} complex in Ca-bearing fluids at elevated temperatures and pressures, however, the effectiveness of dissolved acetate to enhance base metal sulfide solubility is limited.

• OSTI ID: 6038861
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:3; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

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