Batch cooling solution crystallization of ammonium oxalate in the presence of impurities: Study of solubility, supersaturation, and steady-state inhibition

International audienceCompared with equilibrium data in pure solvent, variations of solubility are frequently observed in the presence of dissolved impurities. It is also well-known that impurities can inhibit the crystallization processes and lead to supersaturation barriers below which the growth of crystals is canceled. However, many papers dealing with the inhibiting effects of impurities in solution crystallization are rather unclear about the appropriate way of expressing the supersaturation in impure media. Indeed, as suggested in the present work, the latter can be defined either with respect to the solubility in pure solvent or in reference to the solubility of the impure solvent. Setting the correct reference for computing supersaturation in impure solutions is obviously a key issue for understanding and modeling the dynamics of elementary crystallization phenomena (i.e., primary and secondary nucleation, crystal growth, etc.) The present case study aims at clarifying this point. Solubility data were acquired by in situ ATR FTIR measurements of the concentration of ammonium oxalate in pure water and in impure water containing various concentrations of nickel sulfate dissolved as impurity. Supersaturation thresholds were observed and analyzed, according to the theoretical framework of the Kubota-Mullin impurity adsorption model. The experimental thresholds are attributed to the solubility drifts resulting from the pollution of the pure solvent by impurities. Finally we propose that the impurity-dependent solubility should be considered as the appropriate reference for defining supersaturation

Major and trace element distributions in manganese nodules and micronodules as well as abyssal clay from the Clarion-Clipperton abyssal plain, Northeast Pacific

International audienceThe contents of seven major components (TiO2, Fe2O3, MgO, CaO, Na2O, K2O and P2O5) and 15 trace elements (Sc, V, Cr, Ni, Cu, Sr, Y, Zr, Ba, La, Ce, Nd, Eu, Yb and Th) were determined by ICP-AE spectrometry in 27 samples of manganese nodules, micronodules as well as abyssal clay collected by dredging from an area of nearly 1,9802 nautical miles in the central Clarion-Clipperton abyssal plain at a depth of about 4,500 m. Statistical analyses were used to compare among individual as well as pooled datasets, in addition to different indicators such as La/Th, Ni/Cu and LREE/HREE ratios for the Clarion-Clipperton samples, as well as between these and corresponding values for the upper continental crust (UCC), North America Shale Composite (NASC), and igneous Indian and Pacific Mid-Ocean Ridge Basalts (MORBs). The results show significant correlations between major components in the Clarion-Clipperton samples and Pacific Ocean MORB, whereas trace elements (excepting Ni and Cu) correlate better with the UCC and NASC. There is also depletion in LREEs, together with a Ce negative anomaly for all Clarion-Clipperton samples. The nodule, micronodule and abyssal clay datasets each reveal typical clusters of components such as P2O5 and Y, La, Nd, Eu, Tb, or Ni and Cu. Compared to abyssal clay, the nodule as well as micronodules show significant enrichment in Ni and Cu; nevertheless, an essentially constant Ni/Cu ratio indicates that all samples come from the sediment surface. The distributions of major components as well as trace elements for the Clarion-Clipperton samples present, to different degrees, characteristics common to both the upper continental crust and Mid-Ocean Ridge Basalt, strongly implying a hydrothermal origin, most probably from East Pacific Rise material transported by the Pacific North Equatorial Current

Fluorite's precipitation in KOH solutions in view of removing fluorides from wastewaters

International audienceThe process under study aims at removing dissolved fluorides from effluent waters through the addition of calcium and the precipitation of fluorite in a fluidized bed. In the concept developed at COMURHEX, the effluent is a highly concentrated KOH solution and the calcium is provided as a suspension of portlandite with calcite as an impurity. COMURHEX's target is to achieve an efficient defluorination of KOH solutions prior to recycling and to control the growth of the fluorite grains. Since building a fluorite crystallisation model requires a thermodynamic basis, we started exploring portlandite, calcite and fluorite solubility in concentrated KOH solutions. We are primarily concerned with equilibria in the system Ca(OH)2-CaCO3-CaF2-KOHH2O at temperatures 15 - 35°C in KOH solutions up to 6M (340g/kg). Suspensions and mixtures are prepared in a 3 L stirred reactor under N2 atmosphere and the temperature is varied. Liquid samples are taken from the reactor, filtered, diluted, and analysed by ICP-AES for cations and ionic chromatography for anions, while the solids are washed in ethanol and observed by SEM. In order to choose materials and improve techniques, this work was started with the Ca(OH)2-CaCO3-KOH-H2O subsystem, where solubility data and speciation models are already available from the literature. In this subsystem we experienced the analytical and kinetic difficulties already quoted by other authors. Albeit ICP-AES is very sensitive, Ca analysis is difficult in KOH solutions, because portlandite solubility is low and a matrix effect of potassium weakens the Ca signal, so that its calibration must be performed using KOH solutions rather than conventional (dilute) standards. This problem was overcome by using the standard addition method where the calibrating solutions are prepared at the same KOH concentration as the unknown samples and spiked with increasing amounts of calcium. This method enables the absolute calcium variations to be calibrated and the calcium present as impurities in the KOH parent solution (and thus in the standards) to be evaluated by regression

Le massif de Tiébaghi, Nouvelle Calédonie et ses gîtes de chromite

The Tiebaghi ultramafic massif, Northern New Caledonia, has been the main chromite producer of the island. It is a small, part of a. huge ultramafic nappe tectonically emplaced in the upper Eocene and consists mainly of peridotites with tectonite fabrics. Structural and petrographic field studies showed the main tectonic events and a differenciated rock suite including, from the bottom to the top and from NE to SW, dunites and harzburgites, diopside harzburgites, and spinel lherzolites - locally metamorphosed to plagioclase lherzolites. The main chromite orebodies are located in a few levels within the transition between harzburgitic and lherzolitic units. The morphologies of the orebodies and their structural relations with the host ultramafics result mainly from the strong plastic deformation underwent by the massif. Geochemically, the different ultramafic rock types belong to a rock series, the evolution of which occurs with features similar to the cyclic units and cryptic layering of layered complexes. Spinels and ferromagnesian silicates have suffered different degrees of reequilibration and recristallisation related to the deformations. The Tiebaghi rock series evolution may be explained by the fractional crystallisation of a mixture of a low-Ti and-alkalies tholeiitic basaltic magma and some magnesian olivines (with or without orthopyroxenes and spinels). The chromite concentrations would be the result of pressure drops during the differenciation of the host series, with or without changing magma compositions.Situé au nord de la Nouvelle-Calédonie, le massif de Tiébaghi, d'où a été extraite la majeure partie de la production de chromite de l'île, fait partie de l'ensemble ultramafique calédonien, charrié à l''Eocène supérieur sur le bâti sialique calédonien. Ce massif est constitué presque exclusivement de péridotites à textures de tectonites. L'étude pétrographique et structurale de l'ensemble du massif permet de reconstituer les principales phases de déformation, et de définir l'organisation des roches ultramafiques par une série différenciée clans laquelle les faciès dominants sont successivement, de bas en haut et du Nord-Est au Sud-Ouest, les dunites et harzburgites, les harzburgites à clinopyroxènes et les lherzolites à spinelle - dans ces dernières, le plagioclase apparaît localement par rééquilibrage métamorphique de faciès riches en pyroxènes. Les principales concentrations chromifères se placent suivant un nombre réduit de "niveaux" dans la zone de transition entre les unités harzburgitique et lherzolitique. Les morphologies des gisements et leurs relations structurales avec l'encaissant ultramafique sont contrôlées principalement par les déformations plastiques subies par l'ensemble de la série, Les différents faciès ultramafiques s'intègrent dans une évolution géochimique continue et, dans le détail, séquentielle. Des évolutions, également séquentielles et sans discontinuité majeure entre les différentes unités de la série, apparaissent dans les compositions des minéraux, lesquelles ont pu être modifiées par des rééquilibrages ou des recristallisations partielles en liaison avec les déformations. La différenciation de la série de Tiébaghi peut s'expliquer par la cristallisation fractionnée d'un liquide basaltique tholéitique (pauvre en titane et en alcalins) contenant en suspension - ou imprégnant - un matériel constitué principalement d'olivines magnésiennes, et éventuellement d'orthopyroxènes et de spinelles. Au cours de cette différenciation, des diminutions de pression, accompagnées éventuellement de l'influx de liquides peu différenciés, peuvent être à l'origine des accumulations de chromite

A study on Jurassic Granitic Rocks in the Inje-Hongcheon District, South Korea : I . trace and rare Earth Elements Geochemistry

International audienceInvestigating the trace element behavior, it is revealed that the granitic rocks from the Inje-Hongcheon district show both a systematic variation pattern with SiO2 content for some elements such as Rb, Sr, V, Sc, Ga, Pb and Zn, and a dispersed pattern for Ba, Y, Zr, Nb, TH, Cr and Ni. The systematic variation pattern is recognized in all of the granitic rocks (hornblende-biotite granodiorite, porphyritic biotite granite, equigranular biotite granite and two-mica granite, from center to margin). The dispersed pattern is characteristic in the granitic rocks which occur at the relatively marginal parts. Wether systematic or dispersed pattern in the trace element variation is controlled by the regularity of the weight fraction of the mineral phase containing the element and the supply degree of the element from the contaminant due to wallrock assimilation. The systematic variation pattern is caused by the regular variation of the weight fractions of the mineral phases containing the elements and low supply of elements due to wallrock assimilation. In contrast, the dispersed pattern indicates either dispersive weight fractions of the mineral phases containing the elements or considerable effect of the assimilation. The contents of eight rare eatrh elements (La, Ce, Nd, Sm, Eu, Gd, Dy, Yb) in the hornblende-biotie granodiorite, the porphyritic biotite granite and the equigranular biotite granite decrease with SiO2 content. However, those in the two-mica granite tend to increase with SiO2 content, indicating element enrichment during the solidification of the two-mica granite. The enrichment would be due either to the partitioning of the elements to liquid phase in the granitic system, or to wallrock assimilation.Although the resultant rare earth element (REE) pattern of the model calculation on the basis of Rayleigh fractionisation is similar to overall REE pattern of the granitic rocks, the behavior of the rare earth elements cannot be explained exclusively from simple fractionation. The possibility of wall rock assimilation must be considered

Particle size analysis of metallurgical waste dump for pollutants transport characterization

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Particle size analysis of metallurgical waste dump for pollutants transport characterization

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Compositional variation of Fe-Ti oxides from the Sokli complex, northeastern Finland

International audienceThe phoscorite-carbonatite complex at Sokli, northeastern Finland, is composed of five stages of intrusions of phoscorites and carbonatites (P1-C1, P2-C2, P3-C3 phoscorites and calcite carbonatites, D4 and D5 dolomite carbonatites) which are cut by numerous lamprophyric dikes. Magnetite is ubiquitous in all constituent rock units of the complex and frequently associates with ilmenite. Most ilmenite intergrowths from the Sokli phoscorite-carbonatite complex occur as internal and/or external granules (composite type exsolutions) or sandwich type exsolution lamellae in the host magnetites. Discrete ilmenite crystals are found only in P3 and C3. On the other hand, ilmenites in the ultramafic lamprophyres occur as discrete crystals as well as trellis and sandwich type exsolution lamellae or composite type exsolutions in magnetite. Electron microprobe analyses reveal that magnetite of the Sokli complex belongs essentially to the magnetite-ulvöspinel solid solution series with a small proportion of magnesioferrite. The compositions of magnetite from the Sokli phoscorite-carbonatite complex vary systematically from stage to stage with increasing Fe2+/(Fe2++Mg) ratio, and decreasing Al, Mn and Ti contents. Magnetite from the ultramafic lamprophyre is characterized by large compositional ranges owing to the large amount of mantlederived xenocrysts. Some grains are particularly high in Cr (up to 21.0 wt.% Cr2O3). Aluminous magnesian titanomagnetites are also found, but most magnetites in the ultramafic lamprophyres are pure magnetite. The compositional variation of ilmenite from the Sokli complex is mainly caused by the substitution of Fe2+ into Mg and Mn, and partly Ti into Nb. Mg- and Mn-rich ilmenites in the early stage P1-C1 rocks evolve towards pure FeTiO3 composition in the latest D5 dolomite carbonatite. Ilmenites from the ultramafic lamprophyres are relatively poor in Mn compared to those from the phoscorite-carbonatite complex. In the coexisting magnetite and ilmenite, Mg and Mn cations preferentially partition into ilmenite rather than magnetite. In spite of the mineralogical and geochemical contrasts between the phoscorites and associated carbonatites, compositions of Fe-Ti oxide minerals from the two paired rocks at a given stage are basically the same, and evolve systematically from stage to stage. This supports the hypothesis that the phoscorites and conjugate carbonatites are derived from common parental melts. Furthermore, the intrusions of the Sokli phoscorite-carbonatite complex are considered to have either crystallized from successive batches representing a continuum in time and magmatic evolution, or that the P1-C1 parenta

CO2 disposal into carbonate-dominated reservoirs: where and when Decarbonatation does occur ?

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Patterns of geochemical variability in relation to turbidite facies in the Grès d'Annot Formation

International audienceThe deep marine Grès d'Annot Formation is one of the best exposed analogues to sand-rich turbidite sub-surface systems. Provenance and reservoir heterogeneities have been investigated through a geochemical study of different areas and facies in this formation. Most compositions may be described as mixtures between carbonate and three clastic end-members, i.e. clay, framework grains and a subset of the heavy minerals (zircon, Tioxide, apatite, monazite). These end-members have a nearly uniform chemistry over the studied area and a granite-dominated provenance consistent with a Corsica-Sardinia source hypothesis. This rather uniform provenance makes the Annot Formation a favourable case for exploring the relationships between facies and geochemistry. Not only do different facies differ in average composition, but chemical variations at the bed scale fingerprint the depositional mechanism: archetypal (graded) turbidites and traction-dominated (over-bank) deposits display contrasting variation trends in geochemical plots. The local-scale variation patterns and the general relationship between grain size and chemistry are tentatively integrated in a single differentiation model, providing a rationale for the use of geochemistry in provenance studies, and a possible way to characterize sedimentary facies