Trace metal fractionation as a mean to improve on the management of contaminated sediments from runoff water infiltration basins

The management of stormwater sediment is a key issue for local authorities due to their pollution load and important tonnages. In view of reuse, e.g. for embankment, the environmental evaluation of these highly aggregated sediments requires studying trace metals fractionation and mobility. The distribution of trace metals (Cd, Cr, Cu, Ni, Pb, Zn) and their level of lability in three French stormwater sediments was determined using sequential and kinetic extractions (EDTA reagent) associated with mineralogical analysis and SEM observations. Using microanalysis, new data were acquired on the evolution of aggregate state during extractions and on its significant role in trace metals retention. Trace metals were, in particular, observed to be very stable in small aggregates (10-50 µm). The comparison of the two extraction methods pointed out that EDTA extraction was not convenient to evaluate the stable fraction of Cr, Ni and Zn. Moreover, the results were relevant for basins presenting similar trace metals sources, whatever the physicochemical conditions in basins. The results suggest that the management of stormwater sediments could be improve by a better knowledge of metal mobility, as far as chemical extractions could highlight the localisation of the mobile trace metals fraction. Treatment could be therefore avoided or specific treatment could be applied to a reduced volume of sediments

Formant Structures of Vowels Produced by Stutterers in Normal and Fast Speech Rates

The aim of this study is to analyse the steady--state portion of the first two formants (F1) and (F2) in the production of [CV] sequences, containing vowels [i, a, u], pronounced in two speech rates (normal and fast), by groups of untreated and treated stutterers, and control subjects. Locus equations have been calculated to observe for potential differences in coarticulatory strategies between the three groups. Data analyses reveal a reduction of vowel space for stutterers at a normal speaking rate. When speech rate increases, no reduction of vowel space is noticeable for the latter group of speakers, contrary to treated stutterers and controls. No significant differences between the three groups have been observed in coarticulatory strategies

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

Study of trace metal-bearing phases in sediments from runoff water infiltration basins

La distribution d'éléments trace métalliques (Cd, Cr, Cu, Ni, Pb, Zn) dans les phases solides de sédiments issus de deux bassins d'infiltration de la région nantaise a été étudiée au moyen d'extractions séquentielles et cinétiques associées à des analyses et des observations minéralogiques. Les extractions séquentielles, réalisées selon le schéma du BCR en trois étapes, montrent que la répartition des ETM est relativement comparable entre les deux sédiments, à l'exception du cuivre. Le cadmium est majoritairement lié à la fraction échangeable, le chrome et le nickel sont principalement issus de la fraction résiduelle, le plomb provient en majorité de la fraction réductible, le zinc est concentré dans les fractions échangeable et réductible et le cuivre est soit majoritairement résiduaire pour le bassin de Boisbonne, soit réparti équitablement entre les fractions échangeable, oxydable et réductible pour le bassin de Cheviré. La comparaison avec les extractions cinétiques a permis de montrer le caractère labile ou non extractible des ETM associés aux fractions définies pour les extractions séquentielles. Les observations au microscope électronique à balayage ont confirmé les analyses DRX quant à la composition minéralogique des sédiments et ont mis en évidence la présence d'importants agrégats

Ecoulement et transfert colloïdal dans un milieu modèle à double porosité

Lors de la construction de bassins d’infiltration d’eaux de ruissellement urbaines, les caractéristiques des sols de fond de bassin doivent être prises en compte tant du point de vue du risque de colmatage que de celui du transfert de polluants sous forme dissoute ou particulaire colloïdale. L’hétérogénéité des sols (structure, texture) peut influencer les écoulements d’eau. Une expérimentation en colonne de laboratoire avec un milieu poreux hétérogène en présence ou non d’un géotextile a été menée pour étudier l’influence des conditions hydriques (saturées et non saturées) et de la présence du géotextile sur l’écoulement et le transfert colloïdal. L’analyse des courbes d’élution du traceur de l’eau a montré un écoulement hétérogène dans le gravier. Le degré d’homogénéité de l’écoulement a été augmenté par la présence du géotextile dans les deux conditions hydriques du fait d’une modification de l’écoulement dans la zone proche du géotextile. La rétention colloïdale a été modifiée également en présence du géotextile dans les deux conditions hydriques étudiées. Il est montré que l’introduction d’une strate artificielle dans les bassins d’infiltration peut diminuer le transfert colloïdal en augmentant la capacité filtrante du sol

Effet de l'introduction d'une strate sur le transfert d'eau et de colloïdes dans un milieu sableux

L'effet de l'hétérogénéité du milieu poreux sur l'écoulement et le transfert colloïdal a été étudié en colonnes de laboratoire. Cette hétérogénéité a été créée par l'insertion de macropores artificiels de 0.9mm de diamètre et d'un géotextile dans un milieu sableux. Cette étude confirme la fonction de chemin préférentiel des macropores, dans les sols hétérogènes, pour les solutés et les particules colloïdales, favorisant ainsi le transfert de pollution en conditions saturées. L'introduction d'une strate artificielle peut réduire l'effet des macropores. La rétention colloïdale dépend du degré d'homogénéité de l'écoulement : elle diminue en présence d'un écoulement homogène et augmente quand l'écoulement est hétérogène

Size fractionation of heavy metals in highway runoff waters

International audienceHighway runoff waters may contain pollutants that have accumulated on the carriageway. Numerous field surveys have demonstrated that heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) are common pollutants in highway runoff waters that degrade the quality of natural water bodies [16]. These hazardous pollutants have been found to be attached to particles, especially finer particles than 100 μm, usually quantified by dissolved, suspended and settleable solids measurements [7]. Clay minerals, very fine silts, metallic oxy-hydroxides and organic matter were identified as main components of the composite particulate matter [8, 9]. The knowledge of partitioning of trace metals between the different solids fractions is crucial for stormwater management. The pollutant size distribution determines the efficiency of runoff water treatment by settling in detention basins. Moreover, the toxicity and bioavailability metal characteristics also depend on the speciation of pollutants that could be discharged into natural water bodies. Partitioning of pollutants is also challenging nowadays due to issues of colloid-mediated transfer of heavy metals, as it was already shown for roadside soils impacted by runoff waters

Dynamics of emerging organic pollutants from a municipal landfill

International audienceIn large cities, municipal landfills may have received waste coming from hospitals, but also green waste. The corresponding anthroposol might thus be a source of organic emerging substances such as pharmaceutical or phytosanitary substances. The occurrence and fate of organic emerging substances from such a former landfill in urban areas has been studied as part of a research program dealing with the observation and the monitoring of the environment. Of the 261 substances sought (30 pharmaceutical molecules, 223 phytosanitary products and 8 other emerging substances), 11 pharmaceutical molecules in particular have been quantified in the leachates, 2 endocrine disruptors (bisphenol A and triclosan) and 10 phytosanitary substances. Most of these substances are found also in groundwater immediately downstream of the site (including carbamazepine) at concentrations ranging between 0.1 µg/l and 10 µg/l. The number of detected substances appears much smaller a few hundred meters far from the landfill (bisphenol A and diclofenac in particularly, with concentrations ranging from 0.1 to 1 µg/l and about 0.1 µg/l respectively). Natural attenuation occurs during transfer in the plume, as observed for PAHs or metals. Several mechanisms may explain the natural attenuation of the substances

Reaction of CaClOH with Mullite and Coal Fly Ash at High Temperatures

　　都市固體廢棄物焚化所產生之飛灰含有高含量的氯鹽及微量的重金屬與毒性有機物。氯鹽中的氫氧氯化鈣(CaClOH)會造成飛灰高溫熱處理時產生結塊、粘壁等問題。本研究探討將CaClOH與模來石或燃煤飛灰反應，以分解CaClOH並固定氯的可行性。 　　CaClOH暴露於環境中會吸水潮解。CaClOH/mullite或CaClOH/coal fly ash混合物於高溫反應後會生成wadalite和calcium silicate chloride固體產物以及HCl和H2O氣體產物。反應後試樣水洗後有Friedel''s salt (Ca2Al(OH)6Cl‧2H2O)生成。CaClOH/mullite試樣在莫耳比為2時有最高之非水溶性固體氯含量分率，最高分率隨反應溫度、圓片試樣厚度、進料氣體含水量增加而上升。CaClOH/coal fly ash於高溫反應所生成之非水溶性固體氯含量分率隨反應溫度升高、重量配比減小而上升，且不受coal fly ash種類影響。CaClOH/coal fly ash粉末試樣於相同反應條件下使用coal fly ash所得之非水溶性固體氯含量分率較使用mullite者為高。CaClOH/mullite莫耳比越高(≧2)的粉末試樣，反應後其黏結及黏壁的現象越嚴重。CaClOH/coal fly ash粉末試樣反應後皆有輕微的黏結及黏壁現象。沒有CaO存在下，700℃時CaCl2並不會與mullite反應。　　Fly ash generated from MSW incinerator contains high contents of alkali chlorides and trace amounts of heavy metals and toxic organic chlorides. Calcium hydroxychloride (CaClOH), one of the alkali chlorides, can cause solidification of fly ash in the heat treatment at high temperatures. This work is to study the feasibility of decomposition of CaClOH and fixation of chlorine by reacting CaClOH with mullite or coal fly ash at high temperatures. 　　CaClOH deliquesced when exposed to air. CaClOH reacted with mullite and coal fly ash at high temperatures (700-800℃) to form wadalite (Ca6Al5Si2O16Cl3), calcium silicate chloride (Ca3SiO4Cl2), HCl, and H2O. Friedel''s salt (Ca2Al(OH)6Cl‧2H2O) was found after the reacted sample was washed with water. The distribution of total chlorine in water-soluble salts, water-insoluble salts, and gas phase were mearsured. The highest mole fraction of total chlorine in water-insoluble salts was achieved at a CaClOH/mullite mole ratio of 2; the highest fraction increased with increasing reaction temperature, increasing thickness of disc sample, and increasing water vapor content of the swept gas. When CaClOH reacted with coal fly ash, the mole fraction of total chlorine in water-insoluble salts increased with increasing temperature and with decreasing CaClOH/coal fly ash weight ratio; the source of coal fly ash did not affect the reaction. Under the same reaction conditions, coal fly ash resulted in higher mole fraction of total chlorine in water-insoluble salts than millite. Reacted powder samples of CaClOH/mullite sintered when the mole ratios ≧ 2; all those of CaClOH/coal fly ash slightly sintered. CaCl2 alone did not react with mullite at 700℃

Comparison of physical and chemical methods to characterize trace metals and PAH fractionation in contaminated sediments from runoff water infiltration basins

Trace metals and organic pollutants from urban runoff waters are partly accumulated in soils of retention-infiltration basins. These basins are widely used in urban stormwater management to provide protection from flooding, enhancement of stormwater quality and recharge of aquifers. Within the context of sustainable development, taking sludge management into account would appear necessary in order to maintain both the hydraulic and maintenance functions of these ponds. The recycling of basin sediments is sometimes considered in engineering applications, yet economic suitability and environmental acceptability must still be taken into account. One prerequisite to possible sediment reuse is a strong knowledge of the inherent characteristics of the materials. Among these characteristics, trace metals release availability requires studying trace metals speciation. However, a direct determination of the speciation of an element is often not attainable. In many cases, fractionation can provide useful information on release availability. The aim of this study was therefore to compare various methods of fractionation of both trace metals and organic pollutants in sediments, in view of improving their environmental impact assessment. The methodology was applied to three sediments with various mineralogical and chemical properties. Trace metals (Cd, Cr, Cu, Ni, Pb, Zn) fractionation was determined using sequential and kinetic extractions and a density fractionation. The sequential extractions were conducted using the three-steps BCR protocol. EDTA was used as reagent for kinetic extractions. A chemical extraction using methyl isobutyl ketone (MIBK) was applied to study the speciation of PAH residues in the three sediments. This method was recommended in the literature to obtain a better division of the mineral fraction. The traditional alkali-extraction method of IHSS was also carried out as a reference method on the same materials. Trace metals and PAHs were analyzed in each fraction respectively by ICP-OES and GC-MS. The results of sequential extractions showed quite similar fractionation of trace metals in the three sediments. Cadmium is mainly bound to the exchangeable fraction. Chromium and nickel are mostly present in the residual fraction. Lead lies in the reducible and oxidisable fractions and zinc is concentrated in the exchangeable and reducible fractions. Copper is either mainly in the residual fraction for one specific sediment, or equally distributed in the exchangeable, oxidisable and reducible fractions. The comparison with kinetic extractions let to associate the lability and non-extractability of trace metals to the fractions defined in sequential extractions. SEM observations highlighted that the presence of numerous bulky aggregates in sediments has an impact on the efficiency of extractions and that high energy sonification is required to obtain single particles and small aggregates. It was shown that the MIBK method wasn't a relevant method for the sediment. No additional information was gained by comparison with the IHSS protocol. Finally PAH residues were mainly found in the light fractions and lipidic fractions. Both the strong aggregation state and the origin of pollutants were proving to govern the reactivity of the materials and mainly control the fractionation