Synthèse d'un sulfatoferrate de potassium et son efficacité dans le traitement des eaux

Depuis le milieu du siècle dernier, nous savons que le fer existe à son degré d'oxydation supérieur VI dans l'ion tétraoxoferrate(VI) FeO42-, isostructural de SO42-, CrO42-, MnO42-. Cette espèce mise en solution aqueuse oxyde l'eau en O2, et ce quelque soit le pH de cette solution. La vitesse de cette réaction est très grande en milieu acide, plus lente en milieu alcalin où elle conduit à la précipitation de Fe(OH)3. On peut donc envisager son emploi comme réactif polyfonctionnel : oxydant et floculant, dans le traitement de certaines eaux. La première partie de ce travail décrit une voie originale de synthèse à l'état solide, à la température ambiante, du sel de formule K2(Fe,S)O4, appelé sulfatoferrate de potassium, qui contient l'entité FeO42-. En effet, jusqu'à ce jour seules des synthèses par voie aqueuse, à rendements très faibles, chimiques ou électrochimiques, ont été utilisées pour obtenir FeO42-.Dans une seconde partie, nous avons mesuré les propriétés oxydantes et floculantes du sulfatoferrate de potassium agissant sur deux types d'eaux usées urbaines, chargées (MEST=258 mg.L-1, DCO=549 mg.L-1) et peu chargées (MEST=9 mg.L-1, DCO=37 mg.L- 1). Cette étude effectuée en collaboration avec le Centre International de l'Eau de Nancy (NANC.I.E.) nous a permis de préciser les conditions optimales d'emploi de K2(Fe,S)O4 et de comparer ses performances à celles de FeCl3.6H2O et Al2(SO4)3.18H2O.Sur une eau chargée, l'abattement de la MEST est meilleur avec FeCl3.6H2O et Al2(SO4)3.18H2O, tandis que K2(Fe,S)O4 est plus efficace vis à vis de l'abattement de la DCO.Sur une eau peu chargée, c'est l'effet bactéricide de K2(Fe,S)O4 qui est le plus remarquable; une dose de 10 mg.L-1 en fer (VI) anéantit 99,70% des coliformes totaux et 99,90% des coliformes fécaux.Tetraoxoferrate(VI), FeO42-, possesses properties which make it potentially useful in certain areas of water purification: it is an excellent oxidizing agent, it has a powerful bactericidal action and it spontaneously decomposes over a short period of time. When reduced, the FeO42- ion generates base in solution and a Fe(OH)3 type gel which precipitates and carries down with it other ions (precipitation of hydroxide metal salts). These properties make ferrate(VI) useful in water disinfection and in wastewater treatment because it acts by an oxidation-coagulation-precipitation process. Iron, in its familiar form exists in the (II) and (III) oxidation states; ferrate(VI) ion has long been known, but, due to its instability and difficulty of preparation, it has not been studied extensively and has not been industrially produced. In this paper, we recommend a method of synthesis of alkali ferrate(VI) salts by a dry powder process, which occurs at room temperature and can be easily used for industrial production of Fe(VI). To minimize ferrate(VI) decomposition, we proceed in a strong alkaline medium (presence of a strong base like potash or caustic soda) where oxidation of an iron (bivalent or trivalent) containing salt becomes easier. By such a synthesis process, we produce stabilized ferrate(VI) which enters a solid solution with the formula:M2(Fe,X)O4where M designates Na or K, X is an element whose cation has the electronic structure of a rare gas, e.g. X=S. M2XO4 is an isomorph of K2FeO4 with closed unit cell parameters. The M2(Fe,X)O4 formula has been established by chemical means and by X-ray diffraction; [sup]57Fe Mössbauer spectrometry has been used to monitor the hexavalent iron oxidation state. This paper deals with sulfatoferrate K2(Fe,S)O4 properties for compounds having Fe/S ratios between 1 and 1.5. in aqueous solution, K2(Fe,S)O4 dissolves and gives rise to FeO42- and SO42- anions.In collaboration with NANC.I.E. (Centre International de l'Eau de Nancy), the effectiveness of K2(Fe,S)O4 in wastewater treatment has been studied. The product exhibits a real bactericidal effect on both coliforms and total bacteria. This bactericidal efficiency is reached in a short period of time with iron starting levels as low as 5-10 mg.L-¹. Comparative coagulation jar-tests were carried out on raw wastewater and on secondary effluent using FeCl3·6 H2O, Al2(SO4)3·18 H2O and K2(Fe[inf]0.54,S[inf]0.46)O4. Total suspended solids (TSS) removal on the raw wastewater was better with Al(III) and Fe(III) than with sulfatoferrate. On the secondary effluent, 40% removal was achieved with sulfatoferrate as well as with Fe(III). For removal of chemical oxygen demand (COD), better results were reached with Fe(VI) than with either Fe(III) or Al(III). The effectiveness of FeO42- after 30 minutes of contact with the bacterial medium (secondary effluent) has also been studied. At pH=8.5, a dose of 10 mg.L-¹ iron(VI) removes 99.70% of the total coliforms and 99.90% of the fecal coliforms

Sources and export of particle-borne organic matter during a monsoon flood in a catchment of northern Laos

International audienceThe yields of the tropical rivers of Southeast Asia supply large quantities of carbon to the ocean. The origin and dynamics of particulate organic matter were studied in the Houay Xon River catchment located in northern Laos during the first erosive flood of the rainy season in May 2012. This cultivated catchment is equipped with three successive gauging stations draining areas ranging between 0.2 and 11.6 km2 on the main stem of the permanent stream, and two additional stations draining 0.6 ha hillslopes. In addition, the sequential monitoring of rainwater, overland flow and suspended organic matter compositions was conducted at the 1 m2 plot scale during a storm. The composition of particulate organic matter (total organic carbon and total nitrogen concentrations, δ13C and δ15N) was determined for suspended sediment, soil surface (top 2 cm) and soil subsurface (gullies and riverbanks) samples collected in the catchment (n = 57, 65 and 11, respectively). Hydrograph separation of event water was achieved using water electric conductivity and δ18O measurements for rainfall, overland flow and river water base flow (n = 9, 30 and 57, respectively). The composition of particulate organic matter indicates that upstream suspended sediments mainly originated from cultivated soils labelled by their C3 vegetation cover (upland rice, fallow vegetation and teak plantations). In contrast, channel banks characterized by C4 vegetation (Napier grass) supplied significant quantities of sediment to the river during the flood rising stage at the upstream station as well as in downstream river sections. The highest runoff coefficient (11.7%), sediment specific yield (433 kg ha−1), total organic carbon specific yield (8.3 kg C ha−1) and overland flow contribution (78–100%) were found downstream of reforested areas planted with teaks. Swamps located along the main stream acted as sediment filters and controlled the composition of suspended organic matter. Total organic carbon specific yields were particularly high because they occurred during the first erosive storm of the rainy season, just after the period of slash-and-burn operations in the catchment

The Cosmological Dependence of Cluster Density Profiles

We use N-body simulations to study the shape of mean cluster density and velocity profiles formed via gravitational instability. The dependence of the final structure on both cosmology and initial density field is examined, using a grid of cosmologies and scale-free initial power spectra P\propto k^n. For each model, we stack clusters to define an average density profile in the non-linear regime. The profiles are well fit by a power law over 99% of the cluster volume, with a clear trend toward steeper slopes with both increasing n and decreasing Omega_o. For models with a Omega_o = 0.2, the profile slopes are consistently higher than those for Omega-1.0. Cluster density profiles are thus potentially useful cosmological diagnostics. We find no evidence for a constant density core in any of the models, although the density profiles do tend to flatten at small radii. Much of the flattening is due to the force softening required by the simulations, and an attempt is made to recover the unsoftened profiles assuming angular momentum invariance. The recovered profiles in the Omega=1 cosmologies are consistent with a pure power law up to the highest density contrasts (10^6) accessible with our resolution. The low density models show significant deviations from a power law above density contrasts \sim 10^5. We interpret this curvature as reflecting the non scale-invariant nature of the background cosmology in these models.Comment: uuencoded, 22 pages + 13 figs. Astrophysical Journal, in pres

Assessment of fine scale population genetic diversity and regeneration in Congo basin logged forests

In the Congo Basin most of the light-demanding timber tree species display a deficit of natural regeneration which is a major handicap for sustainable production and certification. Whilst the majority of scientists investigate abiotic and biotic factors explaining that pattern, we hypothesize that tree population density or individual spatial isolation may also affect the tree fitness through inbreeding. In this study, we integrate ecological and genetic approaches to characterize the regeneration potential of a set of priority timber species by (i) estimating pollen dispersal distances at various tree population densities, and (ii) evaluating the impact of increasing spatial isolation on mating characteristics and tree fitness. The ultimate goal is the proposal of minimum population density that prevents inbreeding consequences. Method This ongoing study focuses on 10 timber species (Pericopsis elata, Milicia excelsa, Baillonella toxisperma, Entandrophragma cylindricum, E. utile, E. angolense, E. candollei, Afzelia bipindensis, Erythrophleum suaveloens, Terminalia superba). The data collection was carried out in the logging concession granted to Pallisco in Cameroon. We established two 400-ha plots, where all individuals (DBH > 10 cm) of the target species were inventoried and mapped. A sample of leave or cambium was collected for each of these individuals, as well as for seedlings to characterize patterns of gene flow using genetic tools (nuclear microsatellites). Dispersal agents were identified by direct observations and camera traps. Germination success was characterized in nursery for seeds collected on trees under an increasing isolation gradient. Results Main dispersal agents (wind, bat, rodent) and predators (rodent) were identified for all the species. The gene flow and germination data is still being analyzed and the main results will be presented in the poster. Conclusion Our data will allow characterizing the reproductive biology of a set of important timber species from the Congo basin. These information will strengthen sustainable forest management and the application of certification by adjusting harvesting norms through the use of scientifically-relevant data. In particular, we will tentatively define a maximum distance to be maintained between two adults to allow a qualitative reproduction

Amphibians and Reptiles Captured in Drift Fences in Northwest Wisconsin Pine Barrens

Drift fence surveys were initiated by the Wisconsin Department of Natural Resources (WDNR) in the Crex Meadows Wildlife Area (CMWA) in 1993. Systematic drift fence trapping of amphibians and reptiles in the northwest pine barrens was conducted in a 1996- 97 cooperative effort by the WDNR, the U.S. Forest Service (USFS), and the Great Lakes Indian Fish and Wildlife Commission (GLIFWC). Drift fences were operated in four managed barrens properties, the CMWA, Namekagon Barrens Wildlife Area (NBWA), the Douglas County Wildlife Area (DCWA), and the Moquah Barrens Wildlife Area (MBWA). Eighteen amphibian and reptile species (four salamanders, eight anurans, one turtle, one lizard, four snakes) were captured in ten drift fences in the Northwest Wisconsin Pine Barrens. Fourteen species were captured in the CMWA. The most common species were chorus frogs (Pseudacris triseriata ssp.), wood frogs (Rana sylvatica), and northern spring peepers (P. c. crucifer). The relative abundance of the amphibians and reptiles captured, expressed as mean 1996-97 catch per effort, did not differ between the four managed properties, but species composition did. Only three species were common to all four properties, the blue-spotted salamander (Ambystoma laterale), the eastern American toad (Bufo a. americanus), and the spring peeper. The most likely reason that species composition differs is that the Northwest Wisconsin Pine Barrens is an ecotone for amphibian and reptile species of the western prairies (e.g. tiger salamanders, Ambystoma t. tigrinum) and species of the eastern forests (e.g. spotted salamanders, A. maculatum). All but three tiger salamanders were captured in the southwesternmost property (CMWA) whereas the spotted salamander was captured only in the northeastern-most property (MBWA). Annual variation in CMWA catch/effort rates occurred in total amphibians and reptiles and individual species captured. Total April-May precipitation did not appear to support the catch/effort variation from year to year. However, when broken down into five-day periods, increased catch/effort rates were significantly correlated to precipitation increases, but not to changes in temperature. Timing and amount of precipitation within the breeding season may have impacted herptile movements in the CMWA

Influence of Projection in Cluster Cosmology Studies

Projection tends to skew the mass-observable relation of galaxy clusters by creating a small fraction of severely blended systems, those for which the measured observable property of a cluster is strongly boosted relative to the value of its primary host halo. We examine the bias in cosmological parameter estimates caused by incorrectly assuming a Gaussian (projection-free) mass-observable relation when the true relation is non-Gaussian due to projection. We introduce a mixture model for projection and explore Fisher forecasts for a survey of 5000 sq. deg. to z=1.1 and an equivalent mass threshold of 10^13.7 h^-1 solar masses. Using a blended fraction motivated by optical cluster finding applied to the Millennium Simulation and applying Planck and otherwise weak priors, we find that the biases in Omega_DE and w are significant, being factors of 2.8 and 2.4, respectively, times previous forecast uncertainties. Incorporating eight new degrees of freedom to describe cluster selection with projection increases the forecast uncertainty in Omega_DE and w by similar factors. Knowledge of these additional parameters at the 5% level limits degradation in dark energy constraints to <10% relative to projection-free forecasts. We discuss strategies for using simulations and complementary observations to characterize the fraction of blended clusters and their mass selection properties.Comment: 11 pages, 4 figures to be submitted to phys. rev.

Connaissances, attitudes et pratiques de la dépigmentation cosmétique volontaire dans les lycées, collèges et universités du département des Collines au Bénin

Introduction : la pratique de la dépigmentation cosmétique volontaire est de plus en plus adoptée par les jeunes filles. Ce phénomène de " mode " révèle un certain aspect socio-anthropologique qui assimile la couleur noire de la peau à une vision négative et inférieure de l'être humain. Méthode : il s'agit d'une étude transversale réalisée entre avril et mai 2023 qui a concerné 1039 étudiantes des écoles et universités du département des Collines sélectionnées par sondage aléatoire simple à plusieurs degrés. Résultats : la prévalence de la dépigmentation chez les filles enquêtées est de 78,2%. Les principaux produits utilisés sont les savons à base de dérivé mercuriel et d'hydroquinone (21,55%) et les lotions à base d'hydroquinone et de corticoïdes (75,65). 50% de ces filles savaient ce qu'était la dépigmentation. Pour 82,9% d'entre elles, la couleur de la peau est une représentation d'un critère de beauté et 14,5% l'associent à un critère de classe sociale. Les principales motivations sont entre autres : être plus belle (58,8%) ; unifier le teint (23,0%) ; plaire aux hommes (15,5%) ; à l'occasion d'événements sociologiques tels que le mariage ou le baptême (1,7%) et la rivalité (0,8%). 49,8 % avaient pour complication principale une dyschromie, 24,1 % des vergetures, 14,9 % des dermatites allergiques, 3,3 % de l'acné et 3,0 % des mycoses. Conclusion : la prévalence des dépigmentations enregistrées est très élevée et les actions de sensibilisation ainsi que la rigueur dans le contrôle des produits dépigmentants doivent être renforcées. &nbsp; Introduction: the practice of voluntary cosmetic depigmentation is increasingly being adopted by young girls. This “fashion” phenomenon reveals a certain socio-anthropological aspect, which equates the black color of the skin with a negative and inferior vision of the human being. Method: this is a cross-sectional study carried out between April and May 2023 which involved 1039 female students from schools and universities in the Collines department selected by simple multistage random sampling. Results: the prevalence of depigmentation among the girls surveyed was 78.2%. The main products used were soaps based on mercurial derivative and hydroquinone (21.55%) and lotions based on hydroquinone and corticosteroids (75.65). 50% of these girls knew what depigmentation was. For 82.9% of them, skin color is a representation of a beauty criterion and 14.5% relate it to a social class criterion. The main motivations are among others: to be more beautiful (58.8%); even out the complexion (23.0%); pleasing men (15.5%); on the occasion of sociological events such as marriage or baptisms (1.7%) and rivalry (0.8%). 49.8% had dyschromia as the main complication; 24.1% had stretch marks, 14.9% had allergic dermatitis, 3.3% had acne; and 3.0% had mycoses. Conclusion: the prevalence of depigmentation recorded is very high and awareness-raising actions as well as rigor in the control of depigmenting products should be increased

Connaissances, Attitudes et Pratiques de la Dépigmentation Cosmétique Volontaire des Jeunes Filles en Milieu Scolaire et Universitaire du Département des Collines au Bénin

Introduction : La pratique de la dépigmentation cosmétique volontaire est de plus en plus adoptée par les jeunes filles. Ce phénomène de " mode " révèle un certain aspect socio-anthropologique qui assimile la couleur noire de la peau à une vision négative et inférieure de l'être humain. Objectif: l’objectif est de comprendre ce qui motive les jeunes filles scolarisées à s’adonner à une telle pratique plus spécifquement d‘évaluer leurs connaissances, attitudes et pratiques face à la dépigmentation. Méthode : Il s'agit d'une étude transversale réalisée entre Avril et Mai 2023 qui a concerné 1039 étudiantes des écoles et universités du département des Collines sélectionnées par sondage aléatoire simple à plusieurs degrés. Résultats : La moitié des filles enquêtées savaient que la dépigmentation est l’utilisation de produits chimiques dans le but d’éclaircir la peau. Pour la plupart (82,9%) d’entre elles, la couleur de la peau était une représentation de critère de beauté. Une femme à peau claire avait plus de valeur qu’une femme à peau noire selon 43,0% des enquêtées. 78,2% avaient adopté la pratique de la dépigmentation volontaire et le rythme d’application était biquotidien chez 70,6% d’entre elles.&nbsp; La principale motivation des filles était d’uniformiser le teint. Conclusion : La dépigmentations est un phénomene bien connu des élèves et étudiantes du département des collines.&nbsp; La plupart des enquêtées pratique la dépigmentation et le critère de beauté est utilisé pour justifier le phénomène. &nbsp; Introduction: the practice of voluntary cosmetic depigmentation is increasingly adopted by young girls. This "fashion" phenomenon reveals a certain socio-anthropological aspect that assimilates the black color of the skin to a negative and inferior vision of the human being. Objective:&nbsp; was to understand what motivates young girls at school to engage in such a practice more specifically evaluate their knowledge, attitudes, and practices regarding depigmentation. Method: This is a cross-sectional study carried out between April and May 2023 which involved 1039 female students from schools and universities in the Collines department selected by simple multistage random sampling. Results: Half the girls surveyed knew that depigmentation is the use of chemicals to lighten the skin. For the majority (82.9%) of them, skin color was a representation of beauty criteria. A light-skinned woman was more valuable than a dark-skinned woman, according to 43.0% of respondents. 78.2% have adopted the practice of voluntary depigmentation, and 70.6% of them apply their products twice a day.&nbsp; The girls' main motivation was to even out their skin color. Conclusion: Depigmentation is well known among pupils and students in the hill district.&nbsp; Most of those surveyed practice depigmentation and the criterion of beauty is used to justify the phenomenon

Power Spectra for Cold Dark Matter and its Variants

The bulk of recent cosmological research has focused on the adiabatic cold dark matter model and its simple extensions. Here we present an accurate fitting formula that describes the matter transfer functions of all common variants, including mixed dark matter models. The result is a function of wavenumber, time, and six cosmological parameters: the massive neutrino density, number of neutrino species degenerate in mass, baryon density, Hubble constant, cosmological constant, and spatial curvature. We show how observational constraints---e.g. the shape of the power spectrum, the abundance of clusters and damped Lyman-alpha systems, and the properties of the Lyman-alpha forest--- can be extended to a wide range of cosmologies, including variations in the neutrino and baryon fractions in both high-density and low-density universes.Comment: 20 pages, LaTeX, 4 figures. Submitted to ApJ. Electronic versions of the fitting formula, as well as simple codes to output cosmological quantities (e.g. sigma_8) as a function of parameters and illustrative animations of parameter dependence, are available at http://www.sns.ias.edu/~whu/transfer/transfer.htm