A Pollutant transport investigated through an expansive clay

In the framework of domestic waste disposals, the in-situ compaction of soil is usually used to obtain engineered clay barriers with suitable confining properties. Permeability and pollutant retention are the major properties which should be investigated in this context for barrier evaluation. Considering clay barriers in contact with waste leachates, they may be saturated by solutes of various chemical compositions, including in particular toxic heavy metals. In this context, the expansive Fo-Ca clay, a natural Ca-smectite from the Paris basin of Ypersian (Sparnacian) age, was chosen because of its very low permeability and ability for pollutant retention through cationic exchanges. The smectic is associated with kaolinite (up to 20%), and minor quartz, calcite, goethite and gypsum

High temperature behavior of electrostatic precipitator ash from municipal solid waste combustors

International audienceMunicipal solid waste (MSW) flue gas residues require further treatment prior to disposal or reuse, and vitrification is one of the main solidification-stabilization processes.This paper investigates the high temperature behavior of MSW flue gas residues, performed in laboratory experiments up to 1400°C, and coupled with thermogravimetric analyses, X-ray diffraction, chemical and electron microprobe analyses. Melting temperatures of electrostatic precipitator (ESP) ash are in the range of 1202-1272 °C, whereas semi-dry scrubber residues melt between 1900 and 2300 °C. The mean liquidus temperature of flue gas residues can be simply evaluated as a function of their CaO content, by using the CaO-SiO2-Al2O3 ternary diagram. For ESP ash, the liquidus phase is a Zn-rich aluminous spinel, followed by anorthite at 1225 °C, and melilite at 1190 °C. The total mass loss reaches 18 wt.% at 1300 °C. Moreover, 90% of evaporation takes place below 1000 °C, linked to evaporation of C, Cl, S, Na, K, and of the toxic metals Hg, Cd, Pb, Cu. Due to the high partial pressure of chlorine during heating, chloride is the most probable form of evaporation for Cd, Pb, and Cu. However, most of Zn, Cr, Ni, Sb and Sn remain in the vitrified product

Détermination indirecte des limites d'Atterberg par gravimétrie dynamique.

Ce travail présente une nouvelle méthode de mesure des limites d'Atterberg par dessiccation dynamique. En effet, pour certaines argiles polluées ou des mélanges d'argiles, les méthodes classiques ne peuvent pas être mises en œuvre. Le principe de détermination des limites de liquidité (WL) et plasticité (WP) par cette méthode de dessiccation est présenté. Les valeurs des limites d'Atterberg obtenues sur des argiles courantes se révèlent peu différentes de celles déterminées par la méthode de Casagrande. Ces résultats permettent de considérer cette méthode comme une caractérisation physique des boues argileuse

Phytoremediation of polluted soils : recent progress and developments.: Phytostabilisation of a copper contaminated topsoil aided by basic slags: assessment ofCu mobility and phytoavailability

International audiencePurposeBasic slags are alkaline by-products of the steel industry with potential properties to ameliorate nutrient supply and metal stabilisation in contaminated soils. This study aimed at investigating the potential of a P-spiked Link Donawitz slag and a conventional basic slag called Carmeuse for the aided phytostabilisation of a Cu-contaminated soil at a wood treatment site. The effects of basic slag addition on Cu fractionation, mobility and (phyto) availability were assessed.Materials and methodsBoth slags were incorporated at 1 % w/w into the Cu-contaminated soil phytostabilised with Cu-tolerant plants, using either outdoor lysimeters or a field plot. Untreated soil (UNT), amended soils with the P-spiked Link Donawitz slag (PLDS) and the conventional slag (CARM) respectively, and a control soil (CTRL) were sampled, potted and cultivated with dwarf bean. Physico-chemical analysis, determination of total soil elements and a Cu-sequential extraction scheme were carried out for all soils. Physico-chemical characteristics of soil pore water and Cu speciation (rhizon, ion selective electrode and diffusive gradient in thin film (DGT)) were determined. Shoot dry weight yield and leaf ionome (i.e. all inorganic ions present in the primary leaves) of dwarf beans were investigated.Results and discussionThe slag incorporation at only 1 % w/w increased the soil pH from 1.5 to 2 U and electrical conductivity in soil pore water by three times. The residual Cu fraction increased for both slag amended soils compared to the UNT soil by six times in parallel to the decrease of the Cu oxidisable fraction (1.5 times) and to a less extent the reducible fraction. The incorporation of both slags did not reduce the total dissolved Cu concentration in the soil pore water but significantly reduced the real dissolved Cu concentration ca five times, the Cu labile pool as measured by DGT (at least two times) and the Cu phytoavailability. The dwarf bean total biomass was also improved with the slag addition especially for the P-spiked Linz–Donawitz slag.ConclusionsThe addition of both slags in the contaminated soil increased Cu concentration in the residual fraction and thus reduced its potential mobility. Though the total dissolved Cu soil pore water concentration remained identical, its speciation changed as the real dissolved fraction diminished and lowered the Cu bioavailability. The addition of small amount of P-spiked Linz–Donawitz and Carmeuse slags was beneficial for this Cu-contaminated soil in the context of aided phytostabilisation

Simulation of pollutant transport investigated through an expansive clay.

In the framework of domestic waste disposals, the in-situ compaction of soil is usually used to obtain engineered clay barriers with suitable confining properties. Permeability and pollutant retention are the major properties which should be investigated in this context for barrier evaluation. Considering clay barriers in contact with waste leachates, they may be saturated by solutes of various chemical compositions, including in particular toxic heavy metals. In this context, the expansive Fo-Ca clay, a natural Ca-smectite from the Paris basin of Ypersian (Sparnacian) age, was chosen because of its very low permeability and ability for pollutant retention through cationic exchanges. The smectic is associated with kaolinite (up to 20%), and minor quartz, calcite, goethite and gypsum

Textural and hydration properties of a synthetic montmorillonite compared with a natural Na-exchanged clay analogue.

International audienceAn aluminous montmorillonite has been synthesized at hydrothermal conditions (623 K, 120 MPa) and compared to the natural Na-exchanged Wyoming montmorillonite (Na-SWy2). The synthetic product is characterized by a high cation exchange capacity (83 meq/100g) and ethylene glycol specific surface area (764 m2/g) similar to Na-SWy2 but with a higher purity with one crystalline phase. Compacted smectite samples were percolated with water by using an œdometer cell equipped with a separated injection system, in order to simulate the behaviour of an engineered clay barrier in the context of subsurface waste landfill. Percolation experiments showed very low hydraulic conductivities (10-12 m/s) for both synthetic and natural smectites, in addition to the non macroscopic swelling of the synthetic montmorillonite, in contrast to Na-SWy2. At the nanometric scale, this synthetic clay mineral is characterized by higher hydration states and a better organization in the distribution of water molecules in particles, as proved by X-ray diffraction technique and continuous water vapor gravimetry method. Moreover, adsorption-desorption isotherms of nitrogen revealed the classical feature of swelling clay minerals, and the Brunauer-Emmet-Teller calculation gives a nitrogen specific area of 87 m2/g for the synthetic smectite, twice higher than for the Wyoming clay, due to its higher mesoporosity. Finally, low-pressure argon adsorption coupled with the Derivative Isotherm Simulation procedure highlighted classical adsorption energy distributions of natural phyllosilicates, and thus the synthetic montmorillonite was characterized by an average of 11 layers per particle in the dry state, with basal and edge surface areas different from Na-SWy2

Modelling of metal polluant leaching through a smectite.

International audienceLaboratory tests are performed to characterise the soaking and retention properties of a clay barrier (Fo-Ca) under controlled homogeneous conditions. A physical model that allows calculating the retention properties and kinetics observed during the test is then detailed, and lastly simulations are examined using various soaking conditions. The results show the model predictions of cumulative cation concentrations in leachates (i.e. copper retention by clay). These curves are accurately fit by the model with the experimental data for the leaching phenomena. Clay retention capacity until reaching a physical limit in the exchanges is evidenced as well, with this limit being input into the model as the clay CEC

Lead Isotopic Composition of Fly Ash and Flue Gas Residues from Municipal Solid Waste Combustors in France: Implications for Atmospheric Lead Source Tracing.

Fly ash and flue gas residues from eight municipal solid waste combustors (MSWC) in France (1992-93 and 1998/2002) were analyzed for their Pb isotopic composition. Fly ashes are more representative of solid residual particles, whereas flue gas residues reflect mostly the composition of gas phases. Both sample types contain hundreds to thousands of micrograms of metals per gram. Leaching experiments showed that metals are present in condensed phases, probably as sulfates and chlorides, and suggest that Cd, Pb, and Zn are highly fractionated from one another during volatilization/condensation processes occurring during combustion. Although all the samples analyzed define a fairly restricted range in Pb isotopic compositions (206Pb/207Pb = 1.148-1.158 and 208Pb/206Pb = 2.101-2.114) compared to other environmental samples, some MSWC produce materials having distinct isotopic compositions, whereas others display very similar ones. Isotopic heterogeneity is also measured between samples from a single MSWC. This is interpreted as resulting from the heterogeneity of the waste source materials. The range of Pb isotopic composition of incinerator materials form a well-defined linear array in the 208Pb/206Pb versus 206Pb/207Pb diagram. This array is compatible with the previously reported European standard pollution (ESP) line and most probably represent the average lead isotopic composition of industrial atmospheric emissions in France, with the following ratios: 206Pb/207Pb = 1.154 ± 0.003 and 208Pb/206Pb = 2.107 ± 0.003 (1)

Soil Drainage as an Active Agent of Recent Soil Evolution

International audienceWhile research on pedogenesis mainly focuses on long-term soil formation and most often neglects recent soil evolution in response to human practices or climate changes, this article reviews the impact of artificial subsurface drainage on soil evolution. Artificial drainage is considered as an example of the impact of recent changes in water fluxes on soil evolution over time scales of decades to a century. Results from various classical studies on artificial drainage including hydrological and environmental studies are reviewed and collated with rare studies dealing explicitly with soil morphology changes, in response to artificial drainage. We deduce that soil should react to the perturbations associated with subsurface drainage over time scales that do not exceeding a few decades. Subsurface drainage decreases the intensity of erosion and must i) increase the intensity of the lixiviation and eluviation processes, ii) affect iron and manganese dynamics, and iii) induce heterogeneities in soil evolution at the ten meter scale. Such recent soil evolutions can no longer be neglected as they are mostly irreversible and will probably have unknown, but expectable, feedbacks on crucial soil functions such as the sequestration of soil organic matter or the water available capacity

Interaction argiles-polluants métalliques dans le cadre des centres de stockage de déchets: Expériences d'infiltration sous pression et en batch d'une smectite de référence SWy-2 avec des solutions de zinc

International audienceLe stockage des déchets ménagers et assimilés est devenu un enjeu important pour l'environnement. La réglementation exige la présence d'une barrière de sécurité avec une étanchéité optimale afin d'éviter la contamination du sous-sol. Les smectites, ayant une faible perméabilité et une forte capacité à retenir les polluants, sont donc fréquemment utilisées comme barrière de sécurité passive au fond des alvéoles de stockage. Cependant ces argiles doivent assurer la pérennité de ces barrières en contact avec le lixiviat et particulièrement avec les polluants métalliques qu'il contient. Ce travail consiste à simuler au laboratoire l'infiltration des solutions de polluants métalliques dans les argiles, d'analyser les mécanismes d'interaction et donc de prévoir le comportement hydraulique et physico-chimique de ces argiles. Pour cela, nous utilisons la smectite naturelle de référence SWy2 échangée avec Na+ ou Ca2+ notée Na-SWy2 ou Ca-SWy2. Les échantillons d'argile Na-SWy2 et Ca-SWy2 ont été compactés dans des cellules oedométriques jusqu'à 0,5 MPa, puis infiltrés à une pression constante de 0,3 MPa avec de l'eau pure. La conductivité hydraulique, calculée à partir des volumes injectés et de la loi de Darcy, est très faible, de l'ordre de 10-13 m/s pour les deux types d'argiles, preuve de l'importante étanchéité de cette argile. En complément de ces expériences oedométriques de longue durée (plusieurs mois), des expériences en batch où l'équilibre est atteint rapidement permettent de tester les principaux paramètres qui influent sur les mécanismes d'adsorption. Des essais ont été menés sur Na-SWy2 avec des solutions de Zn(NO3)2 tamponnées à pH=5 avec un rapport solide/liquide de 10 g/L et à force ionique contrôlée mais à différentes concentrations initiales de Zn(NO3)2. La variation du taux de Zn adsorbé en fonction de sa concentration à l'équilibre dans la solution montre que l'adsorption du zinc varie avec la concentration initiale de la solution mère. 80% du zinc initialement mis en solution est adsorbé par l'argile Na-SWy2 à une concentration initiale de 10-5 mol.L-1, représentative des teneurs moyennes dans les lixiviats des centres de stockage. Plus on augmente la concentration initiale de Zn, plus le taux d'adsorption diminue jusqu'à atteindre une valeur de 15% pour la plus forte concentration initiale de 10-2 mol.L-1