FluidNET Abstract GMDM - Tracing the early stages of secondary clay formation using Li isotopes

Tracing the early stages of secondary clay formation using Li isotopes Billarent-Cedillo A.*, Zhang X.Y., Plümper O., King H.E. Department of Earth Sciences, Faculty of Geosciences, Utrecht University. *[email protected] The precipitation of clay minerals is an important mechanism for redistributing elements between the hydrosphere and the solid Earth. This process is prevalent in various geological settings, including deep-sea sediments, river deltas, and soils, making secondary minerals a robust tool for tracing processes at Earth’s surface. Despite extensive research on element cycling and isotope partitioning between clay minerals and water in natural systems, only a handful of studies (Hindshaw et al., 2019, Besselink et al., 2020, Lenhardt et al., 2021) have attempted to examine the clay precursors and their impact on the elemental and isotopic signatures of clays. Investigating these early stages of mineralization is important because materials at the Earth’s surface are often poorly crystallized. In this study, we use Li isotopes to assess the reactivity of these clay precursors. We synthesized aluminosilicate clay precursors using solutions with variable Al/Si ratios (0.5 to 2.5). These solutions were duplicated with the addition of LiCl. We sampled the precipitates formed in the solution and the solution at different time steps over three months. Spectroscopic techniques (Raman, FTIR) and X-ray diffraction (XRD) confirm the amorphous nature of the solids and reveal structural variations in the precursor phases depending on the Al/Si ratio, time, and Li enrichment. Elemental analysis (ICP-OES, ICP-MS) indicates that Li uptake by the amorphous phase varies with the Al/Si ratio. Electron microscopy (SEM, TEM-EDS) further reveals that nanoparticle aggregation is controlled by the Al/Si ratio. Isotopic analysis showed preferential incorporation of ⁶Li into the amorphous phase. Measurements from the solution over time indicated that the Al/Si ratio influences Li isotope fractionation at near-neutral pH, although Li isotope measurements from the final solid phase did not show a clear trend related to the Al/Si ratio. These preliminary results indicate that the initial Al/Si ratio significantly influences both the chemistry and structure of aluminosilicate precursors, as well as the extent of Li uptake. References: Besselink, R., et al. (2020). Crystal Growth & Design. Hindshaw, R. S., et al. (2019). Geochimica et Cosmochimica Acta. Lenhardt, K. R., et al. (2021). Scientific reports.