Zinc-rich clays in supergene non-sulfide zinc deposits

International audienceThe nature and the origin of zinc clays are poorly understood. With the example of the Bou Arhous Zn-Pb ore deposit in the Moroccan High Atlas, this study presents new data for the mineralogical and chemical characterization of barren and zinc clays associated with non-sulfide zinc ores. In the field, white to ocher granular clays are associated with willemite (Zn2SiO4), while red clays fill karst-related cavities cutting across the non-sulfide ore bodies. Red clays (kaolinite, chlorite, illite, and smectite) present evidence of stratification that reflects internal sedimentation processes during the karst evolution. White clays contain 7-Å clay mineral/smectite irregular interstratified minerals with less than 20 % of smectite layers. Willemite is partially dissolved and is surrounded by authigenic zinc clay minerals. Together with XRD results, WDS analyses on newly formed clay aggregates suggest that this interstratified mineral is composed of fraipontite and sauconite. CEC measurements support that zinc is only located within the octahedral sheets. These new results support the following process: (i) dissolution of willemite, leading to release of Si and Zn, (ii) interaction between Zn-Si-rich solutions and residual-detrital clays, and (iii) dissolution of kaolinite and formation of interstratified zinc clay minerals that grew over detrital micas

The Role of IL-15 Deficiency in the Pathogenesis of Virus-Induced Asthma Exacerbations

Rhinovirus infections are the major cause of asthma exacerbations. We hypothesised that IL-15, a cytokine implicated in innate and acquired antiviral immunity, may be deficient in asthma and important in the pathogenesis of asthma exacerbations. We investigated regulation of IL-15 induction by rhinovirus in human macrophages in vitro, IL-15 levels in bronchoalveolar lavage (BAL) fluid and IL-15 induction by rhinovirus in BAL macrophages from asthmatic and control subjects, and related these to outcomes of infection in vivo. Rhinovirus induced IL-15 in macrophages was replication-, NF-κB- and α/β interferon-dependent. BAL macrophage IL-15 induction by rhinovirus was impaired in asthmatics and inversely related to lower respiratory symptom severity during experimental rhinovirus infection. IL-15 levels in BAL fluid were also decreased in asthmatics and inversely related with airway hyperresponsiveness and with virus load during in vivo rhinovirus infection. Deficient IL-15 production in asthma may be important in the pathogenesis of asthma exacerbations

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Conversion of phosphogypsum to potassium sulfate and calcium carbonate in aqueous solution

The dissociation of the phosphogysum by the liquid route which is the object of our work, is most appropriate and little expensive. Indeed, it leads to materials of direct application. The present work has for objective to study the decomposition of the phosphogypsum by the soft chemistry into valuable products such as K2SO4 and CaCO3. K2SO4 is a fertilizer which is highly recommended in the field of the agriculture, while CaCO3 can be used in the fields of the industry (cement) and the environment. According to the obtained results, we notice that the decomposition of the phosphogypsum in aqueous solution is very workable, reproducible, inexpensive and it is an ecologically interesting reaction. This reaction is made at room temperature and in aqueous environment, by giving two valuable products K2SO4 and CaCO3. The reaction is total after one hour and a half

Characterization and origin of clays in the Bou Arhous (Morocco) non-sulfide Zn ore deposit

International audienceSupergene non-sulfide Zn deposits offer high mineralogical diversity including clayminerals that can incorporate significant amounts of Zn like sauconite. Although clayeymaterial is commonly observed in such ore deposits, its nature and origin have beenrarely studied, especially in carbonate-hosting environments. However the role of clayminerals is essential for mineral processing because they usually have a negative impacton zinc recovery.In this work, we focus on the Bou Arhous Zn-Pb ore deposit in Eastern High Atlas,Morocco. This deposit is located in an anticline formed by Lower Jurassic limestoneand marl, with Upper Triassic shale in the core of the anticline. Zn-rich clayey materialfills karstic cavities and two types of clay rich deposits have been identified field: 1)white to ochre granular clay (kaolinite/smectite (K/S) irregular mixed layers, smectiteand illite) and 2) red smooth clay (kaolinite, chlorite, illite). The white to ochre granularclays are closely associated with supergene willemite (zinc silicate), one of the main Znbearing mineral phases of the Bou Arhous deposit. The red smooth clays fillkarst-related cavities cutting across the non-sulfide mineralized bodies. The red smoothclays present evidence of stratification that reflects internal sedimentation processesduring karst evolution. Bulk chemical analyses reveal that the Zn content is highlyvariable in all clayey samples and even can reach several percent. This enrichment maybe due to fine inclusions of zinc silicate or carbonate in the clayey material, or to theoccurrence of Zn clay minerals (i.e. sauconite).The mineralogy of clays and associated minerals in bulk powders and separated <2μmoriented fractions from the two types of clay deposits and from surrounding Triassic toLower Jurassic rocks has been investigated. X-ray diffraction (XRD) analysescomplemented by Scanning Electron Microscope (SEM) observations, have allowed usto identify the nature of the clay minerals and to characterize the textural relationshipsbetween clays and other zinc-bearing minerals like willemite. In a few samples withhigh zinc content (5%), bulk XRD analyses do not reveal the occurrence of zincsulphides, carbonates or silicates, suggesting that zinc is associated with clay minerals.Preliminary XRD results indicate that white and ochre clays are composed ofkaolinite/smectite (K/S) irregular mixed layers with up to 20% of smectite in somesamples; smectite, illite and chlorite are also present. On the other hand, the red clayscontain kaolinite, chlorite, illite, and illite/smectite mixed layers (goethite is commonlypresent in these samples). SEM observations demonstrated that willemite crystals arepartially dissolved and are surrounded by authigenic clay minerals. Microprobeanalyses and cation-exchange capacity on clay mineral fractions are currentlyperformed to highlight the localization of zinc within the structure of clay minerals, andto provide crucial information on Zn recovery potential of the studied deposit. All thesenew results will enable characterizing Zn speciation in these supergene deposits tocheck the following hypotheses for clay origin: 1) interactions between Zn-rich solutiondue to supergene oxidation and residual clays originated from dissolution oflimestone-dominated host rocks, 2) secondary alteration of Zn minerals like willemiteinto clay minerals, and 3) reaction between detrital clays and Zn-rich solutions