Experimental study of aluminum-, calcium-, and magnesium-acetate complexing at 80 degree C

The stabilities of Al-, Ca-, and Mg-acetate complexes were determined separately at 80{degree}C by measuring the solubilities of gibbsite, portlandite, and brucite as functions of acetate concentrations. The experiments were conducted using geologically realistic acetate concentrations in order to observe the acetate complexes that are important in sedimentary basin fluids. The experimental measurements are used to calculate the stoichiometries and thermodynamic properties of the important Al-, Ca-, and Mg-acetate complexes. The data indicate that Al(OAc){sup 2+} and Al(OAc){sup +}{sub 2} are the important Al-acetate complexes in the gibbsite system. Ca(OAc){sup +} and Mg(OAc){sup +} are the dominant acetate complexes in the portlandite and the brucite systems, respectively. The calculated values of the log of the dissociation constants for Al(OAc){sup +}{sub 2}, Al (OAc){sup 2+}, Ca(OAc){sup +}, and Mg(OAc){sup +} are -4.8 {plus minus} 0.2, -2.9 {plus minus} 0.1, -1.2 {plus minus} 0.2, and -1.3 {plus minus} 0.3, respectively. Thermodynamic models that incorporate these results indicate that the presence of acetate in sedimentary basin fluids can not markedly enhance rock porosity through mineral dissolution.