Contribution des colloïdes à la mobilité des contaminants (Pb, As et Sb) (étude spatio-temporelle in situ et test de lixiviation sur un anthroposol développé sur résidus miniers)

La problématique de l évolution des anthroposols développés sur résidus miniers revêt un intérêt majeur pour évaluer les risques de transfert de pollution métallique et métalloïde et de contamination de l environnement. Cette étude a pour objectif de caractériser la contribution des colloïdes à la mobilité du plomb, de l arsenic et de l antimoine dans un anthroposol développé en région Limousin (France) sur des résidus miniers issus d une ancienne mine d or. Pour cela, deux méthodologies différentes mais complémentaires ont été appliquées : une étude spatio-temporelle in situ et des tests de lixiviation en laboratoire. L étude in situ a révélé des fluctuations des paramètres physico-chimiques et chimiques des solutions de sol en fonction de la profondeur et au cours du temps. Il a été observé un comportement différent à l échelle du profil de sol de Pb par rapport à As et Sb, malgré la ressemblance géochimique entre As et Sb. Ces comportements peuvent être expliqués par la nature différente de leurs phases porteuses, ainsi que par les différences de réactivité au cours de la pédogenèse. Dans les solutions de sol, ces phases sont infra micrométriques et/ou nanométriques et leur mobilité est dépendante des conditions physico-chimiques du milieu ainsi que des caractéristiques de la matière organique du sol. Ces résultats montrent l importance de comprendre, à l aide d un suivi in situ, la mobilité des métaux et métalloïdes dans des milieux complexes et riches en matière organique afin d évaluer le risque de pollution lié aux sites et sols pollués. Les tests de lixiviations ont non seulement partiellement reproduit l étude in situ, mais ils ont pu aussi prévoir sur le long terme à la fois la nature des matières organiques lixiviées et une contribution plus importante des colloïdes sur la mobilité des métaux et métalloïdes dans le sol. La complémentarité des tests de lixiviation en laboratoire vis-à-vis de l étude in situ a été avérée.The problem of the evolution of technosols developed upon mine tailings is of major interest for risk assessment related to metal and metalloid transfer, and then, to the environment pollution. In this study, we aimed to investigate the contribution of colloids to the mobility of lead, arsenic and antimony in a technosol developed on mine taillings from a French former gold mine. For that, two different, but complementary methodologies were carried out: in situ spatio-temporal study and in laboratory leaching tests. In the former study, the fluctuations of physico-chemical and chemical parameters of soil solutions were observed according to the depth and over time. The behavior of these elements is different from each other through the soil profile, despite of great geochemical similarity between As and Sb over time. These can be explained by the different nature of their bearing phases and the fact that the reactivities of the latters are not the same during the pedogenesis. However, these phases are infra-micrometric and/or nanometric particles and their mobility is dependent on physical and chemical medium conditions, as well as soil organic matter characteristics. These results highlight the importance of understanding the mobility of metals and metalloids in complex and high organic matter content mediums, with the help of in situ monitoring, in order to evaluate pollution risks associated with contaminated sites and soils. The leaching tests not only partially reproduced in situ study, but also could predict both the nature of leached organic matters and the more important contribution of colloids on the mobility of metal and metalloids in the long term. The complementarity of laboratory leaching tests vis-à-vis in situ study has been proven.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Localisation, distribution et mobilité des ETM dans des sols développés sur roches basaltiques en climat tempéré

De manière à connaître la distribution et la spéciation solide des éléments traces métalliques (ETM) dans les sols issus de l'altération supergène de basaltes et de basanites en climat tempéré, six sols du Massif Central français, soumis à des contextes microclimatiques différents, ont été étudiés. Les roches basaltiques tertiaires et les sols qui s'y sont développés sont riches en Cr (248-455 mg/kg) et en Ni (126-237 mg/kg). Les six sols ont tous des propriétés andiques, sont tous dépourvus d'allophanes mais riches en complexes organo-métalliques. Deux types de sols ont été distingués : andosols et cambisols andiques. Trois approches ont été couplées pour y étudier le devenir et la mobilité potentielle des ETM lors de l'altération supergène. 1) L'étude minéralogique a montré que dans les roches saines, les ETM étaient contenus dans les spinelles chromifères, les titanomagnétites et les silicates ferromagnésiens (forstérites et augites). Les deux principaux facteurs contrôlant la libération des ETM et leur piégeage dans des argiles associées à des oxyhydroxydesauthigènes, sont l'hydrolyse des silicates ferromagnésiens et la résistance des spinelles. 2) L'étude pédologique a mis en évidence les facteurs impliqués dans la distribution des ETM dans les sols développés sur basaltes grâce à deux méthodes quantitatives : les bilans iso-volumiques et les facteurs d'enrichissement. Ces calculs ont mis en évidence le rôle des facteurs pédologiques et lithologiques impliqués dans la distribution des ETM dans les sols. Cette étude a confirmé le contrôle minéralogique sur la distribution de Cr et Ni tandis que la matière organique et les complexes organo - minéraux influencent la distribution de Cu et Zn. Malgré la résistance des minéraux porteurs, Cr et Ni tendent à être conservés dans les cambisols andiques alors qu'ils sont partiellement lessivés dans les andosols situés en contexte plus froid et arrosé. L'influence des constituants organiques se traduit par une immobilisation de Cu et Zn alors que les éléments majeurs sont fortement lessivés (Na, Mg, Ca, Si). 3) Les extractions sélectives ont confirmé pour Cu, l'importance des associations avec les constituants organiques du sol. A la différence de ce qui a été constaté par d'autres auteurs sous des climats plus chauds, ce travail met en évidence la faible mobilité potentielle des ETM dans les sols andiques en climat tempéré montagnardLIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Immobilization of Pb from mine sediments in metakaolin-based geomaterials

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Valorization of mussel and oyster shells toward metakaolin-based alkaline activated material

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Ionomics suggests niche differences between sympatric heathers (Ericaceae)

International audienceBackground and aims: The co-existence of large number of competing plant species with the same basic needs is a major question in ecology, particularly when this involves closely related species. Methods: We investigated the ecology of six heather species (Calluna vulgaris & Erica spp., Ericaceae) able to cohabit in the same heathlands. We characterised the ionome, i.e. the mineral composition of the plants using a sampling strategy specifically designed to control for soil effects. Nine plant communities in Limousin, France, were investigated, representing eight combinations of different species, on serpentine and non-serpentine substrates. Results: Ionome was influenced by both taxonomic and environmental factors with significant interactions between them. We found that species growing in sympatry had distinct ionomic profiles, i.e. they differ in their leaf mineral content, suggesting different nutritional strategies. Different mycorrhizal associations may be hypothesised to explain these different chemical signatures. Conclusions: Differential use of the soil nutrients could explain the co-existence of closely related species. It may also explain the diversity of certain shrubby ecosystems or large shrubby genera such as Erica. Ionomics is therefore a promising tool for ecological studies in non-model organisms

From the Characterization, Geochemical Behavior and Health Risk Assessments of Tunisian Phosphogypsum to a Potential Way of Inerting and Valorization

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Molecular fingerprint of soil organic matter as an indicator of pedogenesis processes in Technosols

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Environmental stability and oral bioaccessibility of synthetic Pb-bearing phases to better evaluate soil health risks

International audienceA large amount of contaminated sites is shown around the world which may induce a health risk due to the presence of contaminants such as metal (loid)s bearing phases. Health risk assessment is based on contaminant bioaccessibility. However, it is needed to understand every contaminant behavior in physiological matrix to be a realistic way to assess and interpret these sanitary risks. Due to the complexity of contaminated soil matrix, the use of synthetic minerals seems to be the better tool to understand their behavior in physiological matrix. Then, this study aims to highlight the environmental stability and the behavior during bioaccessibility ingestion (UBM) of selected synthetic lead-bearing phases. For this purpose, three Pb phases (galena, beudantite, and anglesite) commonly found in contaminated environments (particularly mining sites) were synthesized and characterized (structurally and morphologically). The sequential BCR extractions have shown that most of the lead is in a stable and non-mobilizable form (up to 93%). The lead present in these phases represents very few risks of migrating into the environment during physicochemical condition changes. The results of the bioaccessibility revealed a relatively high stability of the pure bearing phases in the physiological matrix. Lead is stable for 97.0% to 99.2% during the gastric phase and 97.0% to 99.9% during the gastro-intestinal phase. Moreover, the synthetic mixtures of galena/beudantite and anglesite/beudantite have been realized considering the proportions commonly found in the mining contexts. This has shown a similar behavior compared to pure phases except in the case of the anglesite mixture inducing a clear cocktail effect (drastic increase of Pb amount from gastro-intestinal phases). At last, this study is a first and interesting step to assess the behavior of these bearing phases in heterogeneous and complex medium such as soil

A fast one-pot synthesize of crystalline anglesite by hydrothermal synthesis for environmental assessment on pure phase

International audienceAnglesite (PbSO4) is a lead sulfate that belongs to the barite group and is naturally ubiquitous in the environment. This work describes a simple way to synthesize crystalline lead sulfate by using a straightforward hydrothermal procedure. Typically, Pb(NO3)2 and Fe2(SO4)3 precursors were mixed and heated at 94°C for 24h. The synthesized samples have been characterized by coupling X-Ray diffraction (XRD) to spectroscopic methods (FTIR and micro-Raman), X-ray absorption spectroscopy (XAS) and electronic microscopy (SEM and TEM). In fine, the results about this new well crystalline synthetic anglesite confirm the efficiency and the importance of this cheap protocol and the synthesized phases obtained. Moreover, the environmental stability and bioaccessibility of anglesite has been done to evaluate environmental stability of anglesite 2 under various physico-chemical conditions and sanitary risks. Finally, the paper allows to obtain precise data on a pure phase in order to be able to more easily evaluate and understand the role of anglesite in As-polluted sites and soils

Arsenic and lead mobility: From tailing materials to the aqueous compartment

International audienceThis study concerns the mineralogy of the tailings of a former Ag–Pb mine (Auzelles district, France) and the contribution of the waste materials to the heavy metal dissemination in the environment. Accumulation of metals in fish flesh was reported and this pollution is attributed to past mining activities. Tailings were studied to establish the major transfer schemes of As and Pb in order to understand their mobility that leads to contamination of a whole ecosystem. Mineralogical investigation, solubility and compliance tests were performed to assess the stability of the metal-bearing phases. Among the various metallic elements measured, As and Pb show the highest bulk concentrations (up to 0.7% and 6.3% respectively) especially for samples presenting near neutral pH values. According to X-ray diffraction (XRD), Scanning Electron Microscopy (SEM-EDX), Electron Probe Micro-Analysis (EPMA) and micro-Raman spectrometry (μRS), tailings mineralogy still contain primary minerals such as sulfides (e.g., galena, pyrite), phosphates (monazite, apatite) and/or carbonates (e.g., (hydro-)cerussite, dolomite, siderite). Sulfates (e.g., anglesite, lanarkite, plumbojarosite and beudantite) are the main secondary metal-bearing phases with other interesting phases accounting for metals mobility such as Fe and/or Pb and/or Mn oxides (e.g., lepidocrocite, goethite -up to 15 wt% of Pb was measured-, plumboferrite-type phase, mimetite). The lowest Pb solubilities were obtained at pH 8–9 and at a larger range than for As for which the lowest solubilities are reached around pH 6–7. At this minimum solubility pH value, Pb concentrations released still over exceed the National Environmental Quality Standards (NEQS), whatever the samples. The highest solubility is reached at pH 2 for both elements whatever the considered sample. This represents up to 51% of total Pb and up to 46% of total As remobilized and concentrations exceeding the NEQS. As and Pb released mainly depends on the Fe/Mn oxides (e.g., goethite, lepidocrocite) and carbonates (cerussite) which are the less stable phases. Compliance tests also show that Pb concentrations released are higher than the upper limit for hazardous waste landfills. Determination of the mineralogy allows understanding both the solubility and leaching test experiments results, as well as to forecast the impact of the residues on the water quality at a mid-term scale