Hydraulic retention time affects bacterial community structure in an As-rich acid mine drainage (AMD) biotreatment process.

Arsenic removal consecutive to biological iron oxidation and precipitation is an effective process for treating As-rich acid mine drainage (AMD). We studied the effect of hydraulic retention time (HRT)-from 74 to 456 min-in a bench-scale bioreactor exploiting such process. The treatment efficiency was monitored during 19 days, and the final mineralogy and bacterial communities of the biogenic precipitates were characterized by X-ray absorption spectroscopy and high-throughput 16S rRNA gene sequencing. The percentage of Fe(II) oxidation (10-47%) and As removal (19-37%) increased with increasing HRT. Arsenic was trapped in the biogenic precipitates as As(III)-bearing schwertmannite and amorphous ferric arsenate, with a decrease of As/Fe ratio with increasing HRT. The bacterial community in the biogenic precipitate was dominated by Fe-oxidizing bacteria whatever the HRT. The proportion of Gallionella and Ferrovum genera shifted from respectively 65 and 12% at low HRT to 23 and 51% at high HRT, in relation with physicochemical changes in the treated water. aioA genes and Thiomonas genus were detected at all HRT although As(III) oxidation was not evidenced. To our knowledge, this is the first evidence of the role of HRT as a driver of bacterial community structure in bioreactors exploiting microbial Fe(II) oxidation for AMD treatment

Biological attenuation of arsenic and iron in a continuous flow bioreactor treating acid mine drainage (AMD)

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Traitement de la micropollution organostannique aqueuse et sédimentaire par des procédés d’oxydation avancée. TBT-STOP (TBT-Samples Treated by Oxydation Processes)

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Hydrotreatment catalyst preparation: rationalization of impregnation with H4Co2Mo10O386- solutions by quantitative Raman and UV-Vis measurements

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Rationalization of Preparation of Supported Catalysts: Case Study of Decamolybdocobaltates over ?-Alumina

International @ RAFFINAGE+SLOInternational audience1Introduction Among all the steps of preparation of supported catalysts, impregnation is one of the most critical since it de-termines the dispersion and the chemical structure of the metallic species in interaction with the support. Nevertheless, it is not always easy to establish which parameters govern among all the occurring physico-chemical phenom-ena. Therefore, in situ characterization is required to rationalyse preparation of supported catalysts. Simple dissolved salts such as ammonium heptamolybdate, cobalt nitrate usually used for preparation of hydrotreatment (HDT) catalysts are now being replaced by mixed heteropolyanions. Among them, the Anderson-like decamolybdocobaltate H4Co2Mo10O386- is known as a good starting precursor to prepare highly active sulfided CoMo HDT catalyst.[1] In this work, chemistry driving (H4Co2Mo10O38)6- formation and their domains of stability were determined in aqueous solution using Raman and UV-Vis spectroscopies combined with chemometric methods. Parameters relevant of the impregnation step such as the pH, the Co/Mo ratio, and [Mo] were varied.[2] Then, the physico-chemical phenomena occurring during equilibrium impregnation of (H4Co2Mo10O38)6- aqueous solutions over gamma-Al2O3 were described in details crossing different techniques. In this work, we present this investigation carried out through equilibrium impregnation that constitutes an intermediate case between the simulation achieved for (3Co2+; (H4Co2Mo10O38)6-) solution and dry impregnation.The model was then extended to dry impregnation.[3,4] 2Experimental Aqueous solutions of decamolybdocobaltate (H4Co2Mo10O38)6- heteropolyanions were prepared from MoO3, CoCO3 and H2O2 used as oxidizing agent. As the standard conditions lead to a mixture of Anderson monomers and dimers, the preparation was optimized adding a consecutive hydrothermal treatment at 150 °C to obtain pure [H4Co2Mo10O38]6- aqueous solutions for Co/Mo atomic ratio of 0.5. Then, different solutions were prepared with Co/Mo ratio ranging from 0.5 to 0.3 adjusting the pH from 1 to 9. The aqueous solutions as prepared will be labeled xCo:Mo in the following where x is the Co/Mo atomic ratio. The Mo concentration was varied by dilution. Quanti-tative Raman measurements of the different molybdates were obtained from Principal Component Analysis using the SIMPLISMA algorithm [5] and calibrations. UV-Vis spectra afforded quantification of Co3+ and Co2+ cations. Adsorption isotherms were established impregnating in excess 1 g of ?-Al2O3 powder (SBET 285 m2.g-1, pore size 10 nm, pore volume 0.8 mL.g-1, PZC 8) with 4 mL of (3Co2+;(H4Co2Mo10O38)6-) solutions. The mixtures were then filtered off under vacuum to separate the impregnated solids from the excess solutions (filtrates). In addition to the chemical analysis and the pH measured in the solution, both the filtrates and the impregnated supports were characterized by Raman and UV-visible spectroscopies. Finally, Raman and UV spectra of dry impregnated com-pounds were achieved to compare the results. 3Results and discussion It was demonstrated that a mixture of (H4Co2Mo10O38)6- and octomolybdate (Mo8O26)4- species is obtained for Co/Mo ratios lower than 0.5 and the relative quantities of (H4Co2Mo10O38)6- are determined by the presence of (Mo8O26)4- species and by the quantity of Co2+ counter-cations available in the solutions to insure electro-neutrality. Parameters relevant of the impregnation step such as the pH, the Co/Mo ratio and the molybdenum concentration were varied to determine the domains of stability of (H4Co2Mo10O38)6- heteropolyanions after formation. Stable from pH 1 to 4.5, this dimeric Anderson species is destabilized above pH 4.5; Co2+, monomolybdate (MoO4)2- ions and precipitates are then formed. For Co/Mo ratios lower than 0.5, the relative quantity of dimer does not vary with the pH and with a change of the Co/Mo ratio consecutive to the hydrothermal treatment. On the contrary, the co-produced (Mo8O26)4- species can be transformed into other isopolymolybdates varying the pH according to their domains of stability (Figure 1). For all the ratios, (H4Co2Mo10O38)6- dimers were also shown to be stable in a wide range of molybdenum concentration.[2] Fig. 1. Evolutions regards the pH value of (a) Raman, (b) UV-Vis spectra of 0.3Co:Mo aqueous solutions and (c) speciation diagram deduced from Principal Component Analysis. Crossing all the data obtained from the equilibrium impregnations, it was shown that for a surface density lower than 2.5 Mo atoms nm-2, the buffering effect of ?-Al2O3 leads to decomposition of (H4Co2Mo10O38)6- into monomolybdates (MoO4)2- and Co2+ cobalt cations (Figure 2a) that are then adsorbed by electrostatic and covalent interactions with gamma-alumina. Between 2.5 and 3.8 Mo atoms nm-2, MoO42- monomers condense into heptamolybdates (Mo7O24)6- that are then adsorbed by electrostatic interactions and (H4Co2Mo10O38)6- becomes stable because of the lowering of the pH (Figure 2b). Above 3.8 Mo atoms nm-2, the quantities of adsorbed (MoO4)2- and (Mo7O24)6- adsorbed become much smaller than that of electrostatically adsorbed (H4Co2Mo10O38)6-. The physicochemical phenomena occurring are consecutive, i.e., the decomposition of the first molecules and the preferential adsorption of (MoO4)2- compared to dimers allowed the pH to decrease, avoiding the decomposition of the remaining dimers that can then adsorb over ?-Al2O3. The buffering effect of ?-Al2O3 is also limited by the high concentration of impregnation solutions.[3] For dry impregnation, the same physico-chemical phenomena occur considering a given Mo surface density.[3,4] Fig. 2. Schemes deduced from equilibrium impregnations corresponding to (a) decomposition of (H4Co2Mo10O38)6- within gamma-Al2O3 pores and (b) adsorption of preserved (H4Co2Mo10O38)6- in addition to Co2+, (MoO4)2- and condensed (Mo7O24)6- for surface density higher than 2.5 Mo.nm-2. 4Conclusions This work afforded rationalization of preparation of hydrotreatment catalysts from (H4Co2Mo10O38)6- heteropolyanions. The methodology used in this work can be transposed to the preparation of any supported cata-lyst in order to rationalize its preparation, identify the key parameters influencing the catalytic properties, and im-prove these properties. References [1] C. Martin, C. Lamonier, M. Fournier, O. Mentr, V. Harlé, D. Guillaume, E. Payen, Chem. Mater. 17 (2005) 4438-4448. [2] J. Moreau, O. Delpoux, E. Devers, M. Digne, S. Loridant, J. Phys. Chem. A 116 (2012) 263270. [3] J. Moreau, O. Delpoux, E. Devers, M. Digne, S. Loridant, Langmuir 29 (2013) 207-215. [4] J. Moreau, E. Devers, O. Delpoux, M. Digne, S. Loridant, ACS, Division of Energy & Fuels 57 (2012) 697-700. [5] W. Windig, Chemometrics and Intelligent Laboratory Systems 3 (1997) 36

Decamolybdocobaltate Heteropolyanions in Aqueous Solutions: Chemistry Driving Their Formation and Domains of Stability

RAFFINAGE+JMO:SLOIn the present study, aqueous solutions of decamolybdocobaltate H(4)Co(2)Mo(10)O(38)(6-) heteropolyanions were prepared from molybdenum oxide, cobalt carbonate precursors and hydrogen peroxide used as oxidizing agent The preparation was optimized adding a consecutive hydrothermal treatment at 150 degrees C to obtain pure H(4)Co(2)Mo(10)O(38)(6-) aqueous solutions for Co/Mo atomic ratio of 0.5. Combining quantitative Raman and UV-visible measurements and chemometric methods, it was demonstrated that a mixture of H(4)Co(2)Mo(10)O(38)(6-) and octomolybdate Mo(8)O(26)(4-) species is obtained for Co/Mo ratios lower than 0.5, and the relative quantities of H(4)Co(2)Mo(10)O(38)(6-) are determined by the presence of Mo(8)O(26)(4-) species and by the quantity of Co(2+) countercations available in the solutions to ensure the electroneutrality. AS these quantities can be predicted for each Co/Mo ratio, this finding allows rationalization of the preparation of heterogeneous catalysts using impregnation by H(4)Co(2)Mo(10)O(38)(6-) aqueous solutions. Parameters relevant of the impregnation step such as the pH, the Co/Mo ratio; and the molybdenum concentration were varied to determine the domains of stability of H(4)Co(2)Mo(10)O(38)(6-) heteropolyanions after formation. Stable from pH 1 to 4.5, this dimeric Anderson species is destabilized above pH 4.5; Co(2+), monomolybdate MoO(4)(2-) ions, and precipitates are then formed. For Co/Mo ratios lower than 0.5, the relative quantity of dimer does not vary with the pH and with a change of the Co/Mo ratio consecutive to the hydrothermal treatment On the contrary, the coproduced Mo(8)O(26)(4-) species can be transformed into other isopolymolybdates varying the pH according to their domains of stability. For all of the ratios, H(4)Co(2)Mo(10)O(38)(2-) dimers were also shown to be stable in a wide range of molybdenum concentration

HDT catalyst improvement through the careful control of the impregnation step

RAFFINAGE+JMO:SL

Impregnation of Decamolybdocobaltate Heteropolyanions over gamma-Alumina: Detailed Description of the Physico-Chemical Phenomena

RAFFINAGE+JMO:SLOIn this work, the physicochemical phenomena occurring during equilibrium impregnation of Anderson-like decamolybdocobaltate H4Co2Mo10O386- heteropolyanion aqueous solutions over gamma-Al2O3 were described in detail comprising chemical analysis, pH measurements, Raman, and UV-vis spectra. For a surface density lower than 2.5 Mo atoms nm(-2), the buffering effect of the support leads to decomposition of H4Co2Mo10O386- into monomolybdates MoO42- and Co2+ cobalt cations that are then adsorbed by electrostatic and covalent interactions with gamma-alumina. Between 2.5 and 3.8 Mo atoms nm(-2), MoO42- monomers condense into heptamolybdates Mo7O246- that are then adsorbed by electrostatic interactions and H4Co2Mo10O386- becomes stable because of the lowering of the pH. Above 3.8 Mo atoms nm(-2), the quantities of adsorbed MoO42- and Mo7O246- become much smaller than that of electrostatically adsorbed H4Co2Mo10O386-. Adsorption of preserved H4Co2Mo10O386- could be consecutive to the decomposition of the first molecules leading to prior adsorption of MoO42- and Co2+, and decrease in the buffering effect of gamma-Al2O3 and in the pH value. For dry impregnation, the same physicochemical phenomena occur considering a given Mo surface density. The methodology used in this work to rationalize the preparation of hydrotreatment catalysts from H4Co2Mo10O386- heteropolyanions can be transposed to any supported catalyst

A new portable field rotational viscometer for high-temperature melts

co-auteur étrangerInternational audienceMounted on top of furnaces, laboratory viscometers can be used for the rheological characterization of high temperature melts, such as molten rocks (lava). However, there are no instruments capable of measuring the viscosity of large volumes of high temperature melts outside the laboratory at, for example, active lava flows on volcanoes or at industrial sites. In this article, we describe a new instrument designed to be easy to operate, highly mobile, and capable of measuring the viscosity of high temperature liquids and suspensions (<1350 ○ C). The device consists of a torque sensor mounted in line with a stainless-steel shear vane that is immersed in the melt and driven by a motor that rotates the shear vane. In addition, a thermocouple placed between the blades of the shear vane measures the temperature of the melt at the measurement location. An onboard microcomputer records torque, rotation rate, and temperature simultaneously and in real time, thus enabling the characterization of the rheological flow curve of the material as a function of temperature and strain rate. The instrument is calibrated using viscosity standards at low temperatures (20-60 ○ C) and over a wide range of stress (30-3870 Pa), strain rate (0.1-27.9 s −1), and viscosity (10-650 Pa s). High temperature tests were performed in large scale experiments within ∼25 l of lava at temperatures between 1000 and 1350 ○ C to validate the system's performance for future use in natural lava flows. This portable field viscometer was primarily designed to measure the viscosity of geological melts at their relevant temperatures and in their natural state on the flanks of volcanoes, but it could also be used for industrial purposes and beyond