Organomineral interactions: Zoom at nanoscale using EXAFS and MET-EELS

Isabelle BASILE-DOELSCH1,2*, Nithavong CAM1, Clément LEVARD1, Emmanuel DOELSCH2, Jérôme ROSE1

1Aix Marseille Univ, CNRS, IRD, INRA, Coll France, CEREGE, Aix-en-Provence, France; 2CSIRO, Gate 4, Waite Road, Urrbrae SA 5064, Australia; 3CIRAD, UPR Recyclage et risque, F-34398 Montpellier, France

Organo-mineral interactions are recognized as a key factor in stabilizing organic matter (OM) in soils and short-range order mineral phases are increasingly considered as key mineral phases in the control of OM dynamics (Rasmussen et al., 2018). Coprecipitation has been recently proposed as one of the main mechanisms involved. A recent conceptual model proposes that coprecipitates form continuously upon soil mineral weathering in contact with organic compounds of the soil solution (Basile-Doelsch et al., 2015). For silicate minerals, this process imply that Si may also take part in the structure of coprecipitates. However, only Fe and Al coprecipitates have been considered as coprecipitating cations in the literature. Experimental work precipitated nanophases from a solution containing ionic Fe, Al, Si, Mg and K, obtained from a biotite weathered leachate. TEM and Fe K-edge EXAFS showed that they were structured mainly by small oligomers of Fe, together with Si and Al (Tamrat et al., 2018). By adding an organic ligand (DOPA, initial M:C≈1), coprecipitates were structured by a loose and irregular 3D network of small oligmers of Fe, Si and Al forming a highly reactive open-structured mineral skeleton on which OM was bond. A conceptual model of the nanometer-scale structure, animated in 3D, has been proposed (Tamrat et al., 2019) and named “nanoCLICs” for “Nanosized Coprecipitates of inorganic oLIgomers with organiCs”. It differs significantly from the previous models presented for ferrihydrite and amorphous Al(OH)3 coprecipitates (Kleber et al., 2015). We will present the main results that lead to the proposition of the nanoCLICs fine structure model, as well as ongoing imaging of nanoCLICS at nanometer scale by TEM, TEM-EELS and STXM.


Dr I. Basile-Doelsch. MSc in Geology (ENSG, Nancy, France), PhD in Geochemistry for paleoclimatic reconstructions (Vostok ice core, Antarctica), Habilitation à Diriger des Recherches in geochemistry of soils and weathering systems in the critical zone. She is specialized in organomineral interactions in soils. She has been an Aix-Marseille University lecturer since 1998 (France), and a junior member of the prestigious “Institut Universitaire de France” from 2011 to April 2015. As of May 2015, she became a Director of Research at the French INRA institute(CEREGE). She recently spent one year as a visiting scientist in Jeff’s Baldock group at CSIRO Adelaide. or

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