Résumé
Arsenic and uranium are toxic elements that represent a major concern in the management of numerous former mining sites worldwide. Intense research for the last decades has however led to identify natural processes and to draft technologies able to limit the near-field transfer of these redox sensitive elements. For instance arsenic immobilization in acid mine drainage can rely on biooxidation and neutralization reactions that permit arsenic sorption onto iron and aluminum hydroxysulfates and (oxy)hydroxides. To this regard, we will discuss the respective roles of iron(II) and arsenic(III) biooxidation reactions in controlling arsenic removal in a passive bioremediation pilot [1-2]. We will also show that aluminum substitution for iron in ferrihydrite improves the sorption of arsenic(V) but not arsenic(III) during the natural neutralization of acid mine drainage [3]. In parallel, we will present our recent advances on the passive biotreatment of As by sulfate reducing bacteria under acidic conditions, with a special emphasis on the mechanisms ofarsenic sulfides biomineralization [4].In the case of uranium, bioreduction reactions are generally sought or stimulated in order to immobilize this element as insoluble uranium(IV) species. In line with these attenuation pathways, we will put a special focus on the formation and evolution of uranium(IV)-phosphate minerals, such as ningyoite. Indeed, we found these minerals as major uranium hosts in lake sediments [5-6] and wetland soils [7] impacted by former U-mining activities in granitic environments. We will particularly discuss the impact of environmental redox changes in altering the potential of U(IV)-phosphateminerals and non-crystalline U(IV) species for the long-term sequestration of uranium [7-8].[1] Fernandez-Rojo et al. (2017) Water Research 123, 594-606; [2]Fernandez-Rojo et al. (2018) Applied Microbiology and Biotechnology 102,9803–9813; [3] Adra et al. (2016) Applied Geochemistry 64, 2-9; [4] Le Papeet al. (2017) Journal of Hazardous Materials 321, 764-772; [5] Morin et al.(2016) Geochemical Perspective Letters 2, 95-105; [6] Stetten et al. (2017)Geochimica et Cosmochimica Acta 222, 171-186; [7] Stetten et al. (2018)Environmental Science and Technology DOI:10.1021/acs.est.8b0303; [8]Seder-Colomina et al. (2018) Environmental Science and Technology 52,9615-9624.