A MnO2–Co3O4–CaO catalytic pyrolysis method for mercury isotope analysis in marine sediments

Abstract

Mercury (Hg) is a widely distributed toxic pollutant, and its biogeochemical cycling in the environment has attracted considerable attention. Marine sediments are important archives for reconstructing historical and modern Hg fluxes, and Hg stable isotope analysis is a useful tool for tracing their sources and transformation processes. However, the complex matrices of marine sediments pose significant challenges for current sample preparation methods, such as dual-tube furnace pyrolysis, which often results in low and unstable Hg recoveries, along with significant matrix interference, leading to potential biases in Hg concentration and isotope measurements. In this study, we propose a catalytic pyrolysis method that can improve the accuracy and precision of Hg analysis in marine sediments. A composite catalyst consisting of manganese dioxide (MnO₂), cobalt(III) oxide (Co₃O₄), and calcium oxide (CaO) was applied, with optimized temperature ramping and catalyst ratios. Under optimal conditions (50 minutes of heating to 950 °C and 40 minutes of holding, with a catalyst mixture of 70% MnO₂, 20% Co₃O₄, and 10% CaO, nearly 100% Hg recovery was achieved across various sediment types. The method also reduced matrix interference from elements such as tellurium (Te) by more than an order of magnitude. The reliability and accuracy of this method were validated by recoveries and Hg isotope analyses using standard reference materials, natural samples, and mixed samples, providing critical support for tracing mercury sources and reconstructing mercury cycling from marine sediment archives. This approach provides valuable support for tracing Hg sources and reconstructing Hg cycles from marine sediment archives.