The following heterogeneous exchange equilibria have been examined for isotopic effects: CaCO3/Ca(aq.)2⊕. Ca-GBHA/Ca(aq.)2⊕ and Ca(Dowex 50)2⊕/Ca(aq.)2⊕ (GBHA = glyoxal-bis (2-hydroxyanil)). The isotopic ratios 44Ca/40Ca and 48Ca/40Ca were determined by means of a mass spectrometer with a thermal ion source. In the system CaCO3/Ca(aq.)2⊕, the elementary separation factor was found to be less than 1‰ or 0,5‰ per mass unit, respectively.For the exchange in the system Ca-GBHA/Ca(aq.)2⊕ in the concentration range from 0.011 to 0.84 M an elementary separation factor less than 1‰ per mass unit was found; from a three-stage experiment at a calcium concentration of 1.23 M it was concluded that the elementary isotopic effect is less than 0.4‰ per mass unit. Therefore no isotopic fractionation is to be expected for precipitation of inorganic or organic calcium salts.An enrichment of the heavier calcium isotopes in the solution was found in the case of the exchange in a Dowex 50-X12 loaded column. The isotopic effect depends on the concentration of the hydrochloric acid used as the eluent.
Calcium isotopes' place in the diagenetic toolbox
