Elimination of turbidity and bacterial contamination in natural water sources (Ubangi river, Central Africa)

Having access to a natural source of water of sufficiently high quality for human consumption has become a strategic concern for the entire world. In fact, drinking water resources in developing countries are almost non-existent, as they are overused or polluted by intense human activity. Our study aims to develop a natural filter that reduces turbidity and eliminates human pathogens. The process developed should be inexpensive and minimize the use of chemical reagents, and should not be labor intensive. In this context, horizontal sand filtration that uses the natural process of water purification occurring in an aquifer can be regarded as the most suitable water treatment process for developing countries.Disposer d’une source d’eau naturelle de bonne qualité, pour la consommation humaine, est devenu maintenant une préoccupation stratégique pour le monde entier. En effet, les ressources en eaux potables dans les pays en voie de développement sont quasi-inexistantes, car surexploitées ou souillées par une activité humaine intense. L’étude que nous proposons a pour objectif : de mettre au point un filtre naturel qui diminue la turbidité et élimine les agents pathogènes pour l’homme. Le procédé développé peu onéreux devra réduire au maximum l’utilisation de réactifs chimiques, et minimiser toutes interventions humaines. La filtration horizontale sur sable qui utilise le processus naturel de purification de l’eau se produisant dans une nappe aquifère, peut être considéré comme le procédé de traitement de l’eau le plus approprié aux pays en voie de développement et répond aux objectifs fixés.Disponer de una fuente de agua natural de buena calidad, apta para el consumo humano, se ha convertido actualmente en una preocupación estratégica en todo el mundo. En efecto, los recursos de agua potable en los países en vías de desarrollo son prácticamente inexistentes, por exceso de explotación o por contaminación a causa de una actividad humana intensa.El estudio que proponemos tiene por objetivo: desarrollar un filtro natural que reduzca la turbidez y elimine los agentes patógenos perjudiciales para el hombre. El procedimiento desarrollado, de bajo coste, debería reducir al máximo el uso de sustancias químicas reactivas y minimizar cualquier intervención humana. Como la filtración horizontal sobre arena que utiliza el proceso natural de purificación del agua tiene lugar en una capa acuífera, se puede considerar como el procedimiento de tratamiento del agua más adecuado a los países en vías de desarrollo y responde a los objetivos fijados

Chemistry of metal sulfides in anoxic sediments

Using sequential extraction of solid sulfides, the determination of acid volatile sulfides (AVS) and chromium reducible sulfurs (CRS) in anoxic sediments from the Authie Bay (in northern France) has been undertaken because of the importance of the sediments as sinks for iron, sulfur and trace metals and as possible sources of pollution when reduced sediments are mixed with oxic waters (as a result of a sediment remobilization induced by physical disturbances such as tidal currents and dredgings), and subsequently oxidized. Chemical analysis of solutions recovered after sequential leaching of sediments with 1 M HCl, 1 M HF and concentrated HNO3 has enabled us to obtain profiles, s. sediment depth, of trace metals associated with pyrite. Porewater concentration profiles s. depth have been determined for several cations (Ca2+, Cd2+, Cu2+, Fe2+, Mg2+, Mn2+, Na+, Pb2+, Sr2+ and Zn2+) and anions (CO32–, PO43–, SO42– and S2–). Using the chemical equilibrium modeling program MINEQL+ with these analytical data, thermodynamic calculations have given information about the possibility of precipitation of discrete metal sulfide phases (FeS as greigite and amorphous FeS; ZnS, PbS, CuS and CdS), and coprecipitation with adsorption on solid FeS to produce solid solutions with iron sulfides. The degree of trace metal pyritization, DTMP, has been determined for these metals and compared to the degree of pyritization, DOP. The findings suggest that in Authie-bay sediments Mn is well pyritized; whereas Zn, Cu, Ni and above all Cd are weakly pyritized (MnZnCu>NiCd). These observations seem to be intimately related to the existence of the discrete/separate solid phases CuS, CdS and ZnS, as predicted by thermodynamic calculations. Finally, analysis of crude sediments, heavy minerals and pyrite extracted by a heavy liquid density separation method, has been performed with a Raman microprobe to gain information about the geochemical and mineralogical characteristics of these sediments. The efficiency of sequential leachings of sediments (which were used for sedimentary pyrite recovery/attack and analysis of pyritic Fe and trace metal) has also been evaluated by these techniques

Analytical and thermodynamic approach to the mineralogical and compositional studies on anoxic sediments

BACKGROUND, AIM AND SCOPE. The identification of certain minerals directly in the raw sediment has proved to be difficult, if not impossible, because of their instability and/or low contents. This explains why the characterization/composition/crystalline nature of multiple (co)precipitates and solid solutions often necessitate the combined use of density separation methods and macro and microanalytical techniques, and in some cases the possible existence of certain mineral solids is only sustained from thermodynamic considerations. In this context, the comparison of porewater concentration profiles with thermodynamic calculations recently proved to be a convenient way of obtaining clues relative to the potential occurrence of natural minerals. METHODS. Porewaters and sedimentary-solid phases were extracted from sliced sediment samples collected in the Seine estuary (northern France), and studied as a function of sediment depth. Porewater concentration profiles were determined for Ca, Fe, Mg, Mn, Na, P and Sr using inductively coupled plasma atomic emission spectroscopy, and for dissolved sulfur using square wave, cathodic stripping voltammetry. To obtain information about sediment mineralogy, sedimentary solid phases were analysed directly and after density separation with a heavy liquid (CHBr3) by means of several techniques: X-ray diffraction; electron spin resonance and micro-Raman spectroscopies. Furthermore, using sequential extraction procedures, the chemical speciation versus depth of several elements (Al, Ca, Fe, Mg, Mn, P, Pb, Sr, Ti, and Zn) and particularly sulfur [i.e. acid volatile sulfides (AVS) and chromium reducible sulfurs (CRS)] were undertaken. RESULTS AND DISCUSSION. From these analytical data, some thermodynamic calculations [using ion activity products (IAP)] were attempted for the anoxic porewaters where most of the ionic complexing species were measured to support the involvement of relevant geochemical equilibria between these ions and some metals and the existence of any discrete solid phases (calcite, dolomite, greigite and probably vivianite, apatite and siderite), as well as coprecipitates and solid solutions in calcium carbonate. CONCLUSIONS. Thermodynamic equilibria in sedimentary media are rarely achieved because many chemical processes in these systems are established in long periods. Nevertheless, these calculations remain useful to increase our insight into the considered system. They help to support our view about the possible existence of certain minerals (iron sulfides, calcite, dolomite...). They also help account for the real power of ESR for indicating the presence of hypothesised solid solutions, MnxCa1-xCO3. The critical investigations of the authors, however, reveal some weaknesses of XRD and Raman microscopy for identifying minor minerals/precipitates, which result from combinations between the inorganic anions PO43–, CO32– and S2– and the metallic cations Fe2+, Mn2+, Mg2+, and Sr2+

Environmental impacts of heavy metal discharges from a smelter in Deûle-canal sediments (Northern France): concentration levels and chemical distribution

International audienc

On the chemical behavior of sedimentary uranium in Authie Bay (France)

International audienc

Surface characteristics of the iron-oxyhydroxide layer formed during brick coatings by ESEM/EDS, ²³Na and ¹H MAS NMR, and ToF-SIMS

Brick made locally by craftsmen in Bangui (Central African Republic) was modified first by HCl activation and second by iron-oxyhydroxide impregnation through the precipitation of ferric ions by NaOH at various fixed pH values (ranging from 3 to 13). The elemental analyses of synthesized compounds were performed using ICP-AES, and their surface chemistry/properties were investigated by environmental scanning electron microscopy (ESEM/EDS), 1H and 23Na MAS NMR spectroscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The evidence of different 23Na chemical environments and the coexistence of Si and Al bound to ferrihydrite were made. The surface properties of this material which was found to be dependent upon synthesis pH, contributed to enhance metal uptake from water