10:45 AM - 12:15 PM
[BBG01-P02] Molybdenum isotope fractionation during adsorption on manganese oxides
Keywords:birnessite, todorokite, δMnO2, manganese crust, manganese nodules
Molybdenum(Mo) is the most abundant transition element in seawater. Mo is removed by adsorption on manganese(Mn) oxides present in manganese nodules and ferromanganese crusts. In this process, light Mo isotopes are preferentially adsorbed and Mo isotope rations in seawater become heavier. On the other hand, in a reducing environment, Mo precipitates without isotopic fractionation. Fluctuations in Mo isotopic ratios in marine sediments are actively used as an indicator of redox throughout the paleocean. It is known that Mn oxides with different structures, such as low crystallinity and those with layer/tunnel structures, are widely present in the marine environment. It is important to understand how structural differences in Mn oxides affect isotopic fractionation in Mo adsorption. However, because of the difficulty of structural analysis of Mn oxides, no Mo adsorption experiments and isotope measurements have been performed on Mn oxides with well-defined mineral phases. In this study, we synthesize representative Mn oxides in the ocean, adsorb Mo, and perform isotope measurements to determine the effect of structural differences in Mn oxides on isotope fractionation.
Low-crystalline vernadite (δMnO2), layered-structured birnessite and tunnel-structured todolokite were synthesized. X-ray diffraction (XRD) and other methods were used to identify the mineral phases of these manganese oxides. To investigate the effect of the structure of the synthesized Mn oxides, Mo adsorption experiments were performed under common water quality conditions in a glove box with a nitrogen atmosphere. To prepare samples for isotope measurements, adsorption experiments were performed at varying initial Mo concentrations, and the solid and liquid phases were collected separately.
Low-crystalline vernadite (δMnO2), layered-structured birnessite and tunnel-structured todolokite were synthesized. X-ray diffraction (XRD) and other methods were used to identify the mineral phases of these manganese oxides. To investigate the effect of the structure of the synthesized Mn oxides, Mo adsorption experiments were performed under common water quality conditions in a glove box with a nitrogen atmosphere. To prepare samples for isotope measurements, adsorption experiments were performed at varying initial Mo concentrations, and the solid and liquid phases were collected separately.