High-sensitive XANES analysis at Ce L 2 -edge for Ce in bauxites using transition-edge sensors: Implications for Ti-rich geological samples

Accurate determination of cerium (Ce) valence state is important for interpreting the Ce anomaly in geological archives for (paleo)redox reconstruction. However, the routine application of Ce L -edge X-ray absorption near-edge structure (XANES) spectroscopy for detecting trace Ce in geological samples can often be restricted by coexisting titanium (Ti) due to the proximity of their fluorescence emission lines. Therefore, the signal-to-noise ratio of Ce L -edge XANES spectra may not be sufficiently high for high-quality spectroscopic analysis. This study introduces a semi-quantitative approach appropriate for Ti-rich, Ce-dilute geological materials by synchrotron-based X-ray measurement at the Ce L -edge. First, the results confirm that Ce L -edge XANES spectra are able to avoid overlapping Ti K emissions and provide more reliable information on the Ce valence state in Ti-rich materials relative to L -edge XANES. Moreover, the application of transition-edge sensor (TES) could reach the higher sensitivity with better energy resolution than conventional silicon drift detector (SDD) to detect fluorescence X-ray (Ce L ). The investigation on bauxites developed from the Columbia River Basalts shows that combining Ce L -edge XANES and TES allows for resolving weak Ce fluorescence lines at the L -edge from Ti-rich, Ce-dilute samples (Ti/Ce mass ratio up to ∼6000, tens of ppm Ce). The outcome emphasizes the practical possibility of investigating Ce redox state in Ti-rich geological samples.