O-18/O-16 and C-13/C-12 fractionation during the reaction of carbonates with phosphoric acid: Effects of cationic substitution and reaction temperature

The factors for O-18/O-16 fractionation between carbonates and CO2 gas produced by the dissolution of the carbonates in phosphoric acid (sealed vessel method) have been investigated as a function of reaction temperature (20-90 degrees C) and cationic substitution in the solid. Synthetic CaCO3, Ca-0.75 Mn-0.25 CO3, MnCO3, BaCO3 and SrCO3 powders, and a natural kutnahorite sample were used as solids. The delta(18)O values of the gaseous CO2 liberated by the reaction with phosphoric acid decrease with increasing temperature and seem to be a linear function of T(degrees K)(-2). The slopes are specific for different carbonates. No temperature-depended C-13/C-12 fractionation seems to exist.