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Colloïdes et compositions élémentaires des solutions de sols

Abstract : Ubiquitous, dynamic, as well as characterized by important surface complexation ability, colloids are meant to play a key role in trace element sequestration in both waters and soils. This study was aimed on improving the understanding of the role played by colloids in trace element carriage in focusing on: (i) the study of the impact exerted by physico-chemical parameters on the colloidal and elemental composition of the dissolved phase circulating within wetlands, (ii) the colloid genesis ways and their respective role as carriers and vectors of trace elements in waters and soils. The different performed experiments put forward a colloidal control for a lot of trace elements occurring in the soil solution. Some of these latter are strongly complexed by the colloidal pool such as (Al, Cr, U, Mo, Pb, Ti, Th, Fe, and REE), while others are more little complexed (Cu, Cd, Co, and Ni), and a last part which remains unreactive regards to colloids (Li, B, K, Na, Rb, Si, Mg, Sr, Ca, Mn, Ba and V). pH appears to be one major control parameter on the elemental composition of the soil solution, with any pH increase or decrease putting strong impact on the soil solution colloidal and elemental compositions. Furthermore, pH does largely play on the humic substance conformation, which are the main active organic molecules involved in the trace element sequestration within nature, impacting thus their own mobility and that of associated trace elements as well. This study also evidences the occurrence of supramolecular associations of small organic molecules within humic substances, as well as the presence of Fe-nanoparticles intimately bound to organic matter. These latter can sequestrate specific elements such as Pb or Ti. This study allowed also to evaluate the impact of the humic substances on both the Fe oxidation-hydrolysis rate and the size of the precipitated oxyhydroxides. Humic substances slow down and decrease the Fe oxidation-hydrolysis reactions and impact directly the Fe oxide size. Iron is therefore, either as ionic state complexed with humic substances, or as nanoparticles included within an organic matrix. The bioavailability of these Fe-nanoparticles to be used as electron acceptor by Schewanella putrefaciens bacteria during bio-reduction was then tested compared to that of crystallyzed iron in inorganic medium. Mixed Fe-humic substance colloids showed a more important bioavailablity than did inorganic crystallyzed Fe. This latter result evidences that in wetlands, mixed Fe-organic matter colloids represent a major Fe stock, which is regularly requested by microfauna, since much more available than can be that of the geochemical bedrock/soil.
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Contributor : Isabelle Dubigeon <>
Submitted on : Monday, November 8, 2010 - 2:15:00 PM
Last modification on : Thursday, January 14, 2021 - 11:39:34 AM
Long-term archiving on: : Thursday, December 1, 2016 - 11:38:20 PM


  • HAL Id : tel-00533848, version 1



Mathieu Pédrot. Colloïdes et compositions élémentaires des solutions de sols. Géochimie. Université Rennes 1, 2009. Français. ⟨tel-00533848⟩



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