Physics
Scientific paper
Aug 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979gecoa..43.1377w&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 43, Issue 8, pp.1377-1385
Physics
4
Scientific paper
The dissolution behavior of two biogenic Mg-calcites, the echinoid, Tripneustes (12 mol% MgCO 3 ), and the red alga, Neogoniolithon (18 mol% MgCO 3 plus brucite), was studied using free-drift methods in distilled water and phosphate-spiked solutions at 25°C and P CO 2 = 1 atm. Small concentrations of phosphate strongly inhibit dissolution rates. Inhibition increases with increased phosphate levels and with approach toward saturation. Near saturation, dissolution rates are reduced by 10 3 by the presence of 0.6 mol adsorbed-P/m 2 . The magnitude of phosphate inhibition is similar to that observed for low-Mg calcite, and like calcite, the mechanism of inhibition is probably by adsorption of P at surface kink sites. Phosphate appears to inhibit removal of Mg and Ca equally during Mg-calcite dissolution. Rates of brucite dissolution are unaffected by phosphate. Mg-calcites containing >8.5 mol% MgCO 3 should be thermodynamically unstable relative to aragonite in most natural waters. Recent work, however, shows that in contrast to its effect on the behavior of Mg-calcites. phosphate does not inhibit aragonite dissolution. The presence of phosphate might thus reverse the relative stability of these two minerals during diagenesis of shallow marine carbonate sediments.
Hanor Jeffrey S.
Walter Lynn M.
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