Isotopic Fractionations Produced During Direct Air Capture of Carbon Dioxide

1 page.The stable isotope composition of carbonate minerals provides a record of the conditions under which those minerals formed. Carbonate travertine constructions precipitated from high-pH (>11) springs exhibit large and peculiar isotopic variations that are not fully understood, limiting the use of travertine as a paleoenvironmental archive. We carry out laboratory experiments that simulate carbonate travertine formation under controlled conditions (temperature, pH, solution composition, and hydrodynamics) to determine what factors govern their isotopic composition. In our experiments, a CaCl2-K2O solution with no dissolved carbon is brought to high pH by addition of NaOH. The solution is exposed to a N2-CO2 atmosphere whereupon CO2 diffuses into solution and undergoes a series of reactions that lead to the formation of a CaCO3 crust. Data on the mineralogy, morphology, and stable isotope composition of the CaCO3 will be presented. Our experiments also present an opportunity to quantify the rates and limitations of CO2 removal from air by travertine formation