Experimental studies of oxalate complexation at 80 °C: Gibbsite, amorphous silica, and quartz solubilities in oxalate-bearing fluids

Details Experimental studies of oxalate complexation at 80 °C: Gibbsite, amorphous silica, and quartz solubilities in oxalate-bearing fluids Experimental studies of oxalate complexation at 80 °C: Gibbsite, amorphous silica, and quartz solubilities in oxalate-bearing fluids

Nov 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58.4817f&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 58, Issue 22, pp.4817-4829

Computer Science

1

Scientific paper

Experimental measurements of amorphous silica, quartz, and gibbsite solubilities in oxalatebearing solutions at 80°C over a wide pH range reveal that aqueous Si-oxalate complexation is of negligible importance in natural fluid-rock systems, but that Al-oxalate complexation can dramatically affect aqueous Al concentrations. The data indicate the presence of at least two Al-oxalate complexes, and the data place quantitative constraints on the stoichiometry and stability of the Al-oxalate aqueous species. However, the data do not uniquely define the stoichiometries of the important Al-oxalate complexes. The two most likely possibilities are 1. (1) Al(Ox) 3 3- and Al(Ox) + as the important complexes or 2. (2) Al(OH) 2 Ox -1 and Al(OH)Ox 0 . For the first speciation, the observed solubilities constrain the values for the log of the dissociation constants for Al(Ox) 3 3- and Al(Ox) + to be -18.1 ± 0.5 and -8.3 ± 0.7, respectively. If Al(OH) 2 Ox - and Al(OH)Ox 0 are dominant, the data define the dissociation constants for these complexes to be -24.5 ± 0.2 and -15.8 ± 0.5, respectively. Thermodynamic modeling, using these results, indicates that Al-oxalate complexation can dominate the Al budget of formation waters. Calculations suggest that with Al(Ox) 3 3- and Al(Ox) + dominant, the presence of a significant concentration of Ca (on the order of 200-300 ppm) does not imply a sequestering of oxalate by a Ca-oxalate precipitate. However, if Al(OH)Ox 0 and Al(OH) 2 Ox - are the dominant Al-oxalate complexes, Ca-oxalate precipitation will occur at much lower Ca concentrations.

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