Partitioning of 13C and 12C on the degassing of CO2 and the precipitation of calcite - Rayleigh-type fractionation and a kinetic model.

Abstract

Calcite is not precipitated immediately from a supersaturated Ca-bicarbonate solution that becomes supersaturated by degassing CO2. The degree of supersaturation increases until calcite begins to precipitate. Over the whole range of the initial CO2-degassing and the subsequent precipitation, the carbon isotope composition of the dissolved carbonate changes systematically. Measurements at the calcite-precipitating spring of Guterstein, Germany indicate that this variation is controlled kinetically and cannot be attributed to a Rayleigh-type fractionation. An analytical expression for a kinetic model is derived. From this expression the ratio of rate constants for 13C- and 12C-species, controlling the partitioning, can be obtained.-Authors