Multi-isotope (Ba, C, O) partitioning during experimental carbonatization of a hyper-alkaline solution

Carbonates formed from hyperalkaline aqueous solutions at the Earths surface are known to bear the most extreme disequilibrium isotope signaturesreported so far in nature. We present here the results for stable carbon (C), oxygen (O), and barium (Ba) isotope fractionationduring the precipitation of witherite(BaCO3) induced by the chemical absorption of atmospheric carbon dioxide (CO2) into an aqueous hyper-alkaline solution (at 4° and 21 °C; 1 atm total pressure). Independent from temperature, the barium carbonateformation was associated with a substantial enrichment of the lighter C and O isotopesin the solid compared to the atmosphere (C, O), close to previous results found in experiments and nature. A new approach is introduced to explain oxygen isotope fractionationupon hydroxylation of CO2. With Ba isotope enrichment factorsbetween −0.45 and −0.53‰ (138/134e) or −0.34 and −0.40‰ (137/134e), respectively, the synthesized BaCO3 displays the highest kinetic enrichment of the light Ba isotopein the carbonate solid reported so far.