Mechanisms of formation and reactivity of imogolite types material

Reactivity of nanopar8cles represents a central issue for many laboratories around the world. Among many supported efforts the control of the morphology of nanopar8cles is mo8vated by the fact that morphology strongly influence the proper8es of the final products. Among the vast family of available nanopar8cles, imogolite is a clay nanotube for which perfect control of the diameter is possible. Imogolites were first observed in volcanic soils[1]. They are natural aluminosilicate nanotubes having the general formula (OH)3Al2O3SiOH with a 2 nm external diameter and up to micrometers in length. The impressive monodispersity in imogolite nanotube diameter has mo8vated research on their forma8on mechanism. Synthesis protocols to produce imogolite were quickly developed. Farmer et al. were the first to obtain synthe8c imogolite using low concentra8ons of AlCl3 and SiO 2 monomers as star8ng materials (millimolar concentra8ons of the reagents) [2]. However, the produc8on of large amount of imogolite or imogolite type materials remained challenging for long 8me. We will present our most recent results concerning the possibility to produce imogolite type materials from highly concentrated stock solu8ons. We will also detail the possibility to form double wall Al- Ge nanotubes and the different stages of their forma8on [3-7]. We will then detail the surface reac8vity of these nanotubes toward metals at he lab scale as well as in natural soil. (Résumé d'auteur

Copper and zinc speciation in pig slurry: implications on mobility and bioavailability in soils

The fate of pollutants associated with organic wastes is a key issue. For example, pig slurry presents high concentration of Copper (Cu) and Zinc (Zn) since they are used (at high concentration) as essential micronutrients in animal feeds. As a consequence, Cu and Zn accumulation was measured in soil surface layers that had been amended with pig slurry, inducing phytotoxicity as well as groundwater quality degradation. Better prediction of the mobility and bioavailability of Cu and Zn from pig slurry spreading can be achieved by determining the speciation of these elements. The aim of this study is to investigate Cu and Zn speciation in pig slurry. A multitechnique approach was adopted including size fractionation, XRD, SEM-EDS, ?XRF and XAS. The present study demonstrated that only 0.2% of total Cu or Zn present in pig slurry was bound to particles smaller than 0.45 ?m, while 75% of total Cu and Zn was bound to particles in the 0.45-20 ?m size range. ?XRF highlighted the colocalisation of Cu and sulfur. In addition, geochemical modelling demonstrated that physical chemical conditions within pig slurry lagoon are compatible with the precipitation of chalcocite (Cu2S). Finally, XANES shows that Cu speciation in raw pig slurry and size fractions is described by Cu2S and that its oxidation state is Cu(I). These Cu speciation in pig slurry may be the main reason for the observed Cu accumulation at the soil surface. Zn speciation revealed three patterns 49% Zn bound to organic matter, 37% amorphous Zn hydroxide, and 14% sphalerite (ZnS). The detected presence Zn sulphide, was unexpected and is reported for the first time. These three Zn forms seemed to be soluble in neutral or weakly acid soil systems, so the long-term impact of pig slurry spreading could lead to Zn leaching. (Résumé d'auteur

Apport de la cristallochimie et de la spéciation du chrome et du vanadium à la modélisation de l'altération de granulats artificiels (sous-produits d'aciérie)

Cofinancement ADEME/INERISThe pig iron conversion into steel generates a large quantity of residue, the Basic Oxygen Furnace steel slag (BOF slag), partially reused as aggregates in civil engineering. The objective of this study is to quantify and to explain the BOF slag leaching behavior (alteration and trace metals (Cr, V) release) by the identification of the molecular mechanisms which control the elements mobility within the solid phase. The experimental study is based on leaching tests (at a laboratory scale with CTG-Leachcrete and at a field-scale with lysimeter) and on X-ray absorption and fluorescence spectroscopies. This approach permits to identify elements speciation at an atomic scale : i.e. their oxidation state, symmetry and bearing phase(s).Trivalent Cr, very stable in a dicalcium ferrite, is very few released during leaching tests in laboratory and in lysimeter. And a spinel-type phase, obtained from (Fe, Mn, Mg)O alteration, also controls the Cr(III) mobility. On the other hand, V(III) is oxidized to V(V) within its bearing-phase. It explains V release during laboratory tests.These experimental data allowed to establish the thermodynamic equations describing BOF slag alteration (mineralogical evolution and release curves obtained from static and dynamic leaching tests), which are the basis of geochemical modeling (CHESS). Such model aims at predicting BOF slag long-term behavior.Dans les aciéries, la conversion de la fonte en acier est une opération qui génère des quantités très importantes de déchets : les laitiers d'aciérie de conversion (LAC), qui sont en partie valorisés en tant que granulats en génie civil. Cette thèse vise à quantifier et à expliquer le comportement à la lixiviation des LAC, c'est-à-dire leur altération et le relargage des métaux traces (Cr, V) qu'ils contiennent, par l'identification des mécanismes physico-chimiques qui régissent, au sein même de la matrice solide, la mobilité et le transfert des éléments. L'approche expérimentale choisie est basée sur des tests de lixiviation (en laboratoire à l'aide du CTG-Leachcrete et en lysimètre à l'échelle semi-pilote) et des spectroscopies d'absorption et de fluorescence des rayons X permettant de caractériser à l'échelle du site cristallochimique le degré d'oxydation, la symétrie et la nature des phases porteuses des éléments.Le Cr exclusivement trivalent, très stable dans les sites octaédriques d'une ferrite de calcium, est très peu relargué lors des tests de lixiviation en laboratoire et en lysimètre. Une phase de type spinelle, issue de l'altération de (Fe, Mn, Mg)O contrôle également la mobilité du Cr(III). Au contraire, le V(III) subit une oxydation en V(V) au sein même de sa phase porteuse, qui s'accompagne d'une perte de symétrie, à l'origine de sa mobilité à l'échelle du laboratoire.Les données issues de ces expériences ont permis d'écrire les équations thermodynamiques d'équilibre à l'origine de l'initialisation d'un modèle géochimique robuste (CHESS) reproduisant l'altération des LAC : évolution minéralogique et courbes cinétiques de relargage obtenues lors des tests de lixiviation statique et dynamique en laboratoire. Ce modèle vise à terme à prédire le comportement à long terme des LAC dans un scénario de valorisation donné

Imogolites as a tool for evaluating the hazard of HARN

Since the discovery of carbon nanotubes (NTs), there has been great interest in the synthesis and characterization of similar shaped structures like inorganic nanotubes, nanorods, or nanowires. Imogolites (Al2SiO3 (OH)4) are natural aluminosilicate single wall nanotubes. To date, only Ge-Al imogolite analogues have been successfully synthesized 100 times more concentrated than Si-Al imogolites. The growth mechanisms of imogolite-like aluminogermanate nanotubes were examined using a combination of local- (XAS at the Ge-Kedge and 27Al NMR) and semilocal scale techniques (in situ SAXS). A model is proposed for the precursors of the nanotubular structure and consist in rooftileshaped particles, up to 5 nm in size, with ca. 26% of Ge vacancies and varying curvatures. These precursors assemble to form short nanotubes/nanorings observed during the aging process. The final products are most likely obtained by an edge-edge assembly of these short nanotube segments. Two structures are revealed by SAXS: at 0.25M of Al the Al-Ge imogolite are double-walled NTs whereas at 0.5 M single-walled NTs are obtained. First tests to reveal cyto and genotoxicity on various vertebrates cells (human fibroblasts and CHO-K1) are interesting. They show a genotoxicity for concentrations from 8 10-5 g/L and effects decreasing from proto-imogolite to long tube. (Texte intégral

Environmental assessment of the behavior of a BOF steel slag used in road construction : the PRECODD-ECLAIR research program

International audienceSteel production generate great amounts of by-products as steel slags. The use of Basic Oxygen Furnace slags (BOF slags) has been restrained due to insufficient volume stability, and due to the lack of environmental regulations. The purpose of the PRECODD-ECLAIR research program is to develop a behavior model based on a multi-scale physico-chemical, mechanical, hydrodynamic and ecotoxicological characterizations of a BOF slag used in a public works scenario. This paper aims at presenting the overall ECLAIR research program, the equipped experimental platform constructed using a BOF steel slag, and the first results of the slag characterization

Effect of pH and pressure on uranium removal from drinking water using NF/RO membranes

International audienceGroundwater is becoming an increasingly important drinking water source. However, the use of groundwater for potable purposes can lead to chronic human exposure to geogenic contaminants, for example, uranium. Nanofiltration (NF) and reverse osmosis (RO) processes are used for drinking water purification, and it is important to understand how contaminants interact with membranes since accumulation of contaminants to the membrane surface can lead to fouling, performance decline and possible breakthrough of contaminants. During the current study laboratory experiments were conducted using NF (TFC-SR2) and RO (BW30) membranes to establish the behavior of uranium across pH (3-10) and pressure (5-15 bar) ranges. The results showed that important determinants of uranium membrane sorption interactions were (1) the uranium speciation (uranium species valence and size in relation to membrane surface charge and pore size) and (ii) concentration polarization, depending on the pH values. The results show that it is important to monitor sorption of uranium to membranes, which is controlled by pH and concentration polarization, and, if necessary, adjust those parameters controlling uranium sorption

Characterization and pH Dependent Leaching Behavior of Tunisian Phosphogypsum

The current study aims to characterize and as well as to investigate the leaching behavior of Tunisian Phosphogypsum (PG). The results of the physical characterization studies showed that, as worldwide Phosphogypsum, the Tunisian PG behaves like fine silty sand with important initial water content. Relevant attention was given to the leaching behavior of the sample which was subjected to two leaching tests according EN 12457-2 (2002)  at liquid to solid ratios (L/S) of 10 and 100 as well as pH stat leaching test according to the CEN/TS 14997 (2006). The progressive release of major elements as well as the metals indicates high mobility of the most analysis elements. Calcium, sulfate and phosphorus were the major elements having the highest leaching concentrations. Broadly, mobility of trace metals in PG was classified into three degrees: elements with high mobility were Sr, Zn, those with moderate mobility were As, Ba, Cd and Cr and those with low mobility were Cu, Ni, Pb, Se, V, Y and Zr. The highest concentrations of the most part of the metals were obtained from L/S 100. Based on the pH dependent leaching experiments, results show that the PG has a maximum susceptibility to leaching out metals when exposed to a strongly acidic condition (2-4). While, alkaline condition appears to be the most stable for the analyzed material. This paper offers a data base which is useful when later recycling actions are taken. Indeed, acidic conditions should be avoided in order to prevent metal leaching from PG.

Investigation of copper and zinc speciation in pig slurry by a multitechnique approach

Copper (Cu) and Zinc (Zn) occurs in high quantity in pig slurry since they are used as essential micronutrients at high concentrations in animal feeds despite the low Cu and Zn assimilation by pigs. Cu and Zn accumulation was therefore measured in soil surface layers that had been amended with pig slurry, while also determining the phytotoxicity as well as the extent of groundwater quality degradation. Better prediction of the mobility and bioavailability of Cu and Zn from pig slurry spreading can be achieved by determining the speciation of this element in addition to its total concentration. The aim of this study was to present a multitechnique approach to investigate Cu and Zn speciation in pig slurry. Size fractionation was first carried out to account for the complexity of pig slurry. Then X-ray diffraction (XRD), scanning electron microscopy, coupled with energy dispersive spectrometer (SEM-EDS), Micro X-ray fluorescence spectroscopy (?XRF) and extended X-ray absorption fine structure (EXAFS) or X-ray absorption near-edge structure spectroscopy (XANES) analyses were combined to assess Cu and Zn speciation. The present study demonstrated that only 0.2% of total Cu or Zn present in pig slurry was bound to particles with a size less than 0.45 ?m, while 75% of total Cu and Zn was bound to particles in the 0.45-20 ?m size range. ?XRF highlighted the colocalisation of Cu and sulfur (S). In addition, geochemical modelling demonstrated that physical chemical conditions within pig slurry lagoon are compatible with the precipitation of chalcocite (Cu2S). Finally, XANES shows that Cu speciation in raw pig slurry and size fractions is described by Cu2S and that its oxidation state is Cu(I). These Cu speciation in pig slurry may be the main reason for the observed Cu accumulation at the the soil surface. Zn speciation revealed three patterns 49% Zn bound to organic matter, 37% amorphous Zn hydroxide, and 14% sphalerite. The detected presence of sphalerite, or Zn sulphide, was unexpected and is reported for the first time. These three Zn forms seemed to be soluble in neutral or weakly acid soil systems, so the long-term impact of pig slurry spreading could lead to Zn leaching. (Texte intégral

Interplay of coprecipitation and adsorption processes: Deciphering amorphous mineral–organic associations under both forest and cropland conditions

Mineral–organic associations are crucial carbon and nutrient reservoirs in soils. However, conversion from forest to agricultural systems disrupts these associations, leading to carbon loss and reduced soil fertility in croplands. Identifying the types of mineral–organic associations within a single soil is already challenging, and detecting those susceptible to disruption during forest-to-crop conversion is even more complex. Yet, addressing this identification challenge is essential for devising strategies to preserve organic matter in croplands. Here, we aimed to identify the predominant mineral–organic associations within an Andosol (developed on Fe-poor parent material) under both forest and cropland conditions. To achieve this, we collected Andosol samples from both a forested and a cultivated area, located 300 m apart. We then analyzed differences between the two soil profiles in soil physicochemical parameters and characterized mineral–organic associations using an array of spectro-microscopic techniques for comprehensive structural and compositional analysis. At microscale and nanoscale spatial resolution, we observed mineral–organic associations in the form of amorphous coprecipitates, composed of a mix of C+Al+Si and C+Al+Fe+Si nanoCLICs (inorganic oligomers with organics), proto-imogolites and organic matter, some Fe nanophases associated with organic matter, and some metal–organic complexes. This challenges prior conceptions of mineral–organic associations in Andosols by demonstrating the presence of amorphous coprecipitates rather than solely organic matter associated with short-range-order minerals (i.e., imogolite and allophanes). Moreover, chemical mappings suggested that these amorphous coprecipitates may adhere to mineral surfaces (i.e., phyllosilicates and imogolites), revealing secondary interactions of mineral–organic associations in soils. While the presence of similar amorphous coprecipitates in both the forest and crop Andosols was confirmed, the crop soil had 75 % less C in mineral–organic associations (in the 0–30 cm depth). Although the sample size for comparing land use types is limited, these results suggest that the nature of mineral–organic associations remains identical despite quantitative differences. This study highlights the crucial role of amorphous coprecipitates in C stabilization in Andosols and also suggests their vulnerability to disruption after 30 years of a forest-to-crop conversion, thereby challenging our understanding of the persistence of mineral–organic associations in Andosols