Temperature dependence of oxygen isotope fractionation of CO₂ from magnesite-phosphoric acid reaction

Abstract

New experimental results are reported on oxygen isotope fractionation factors, α_T, between the δ¹⁸O compositions of carbon dioxide liberated by phosphoric acid in the temperature interval of 323 to 373K and that of total oxygen from a natural magnesite (MgCO₃). These results are distinctly different from some previously published mutually inconsistent data, and can be expressed as a linear relationship: 10³ lnα_T = [{(6.845 ± 0.475)^∗ 10⁵}/T²] + (4.22 ± 0.08), where 10³ lnα_T refers to fractionation at different temperatures T in Kelvin. Fractionation factors have also been determined at 323 and 368K on a natural calcite. The results on calcite are in excellent agreement with previously published data and can be written as:10³ lnα_T = [{(5.608 ± 0.151)10⁵}/T²] + (3.89 ± 0.08). The combined results on magnesite and calcite yield a computed value of α = 1.01117 for dolomite at 298K, assuming equal proportion of 0.5 mole of magnesium and calcium in dolomite, the previously reported experimental values being 1.01109 and 1.01110.