12 research outputs found
Leaching of fluoride from biotite mica in soil : implications for fluoride in shallow groundwater
Leaching of Fâ from biotite was investigated at room temperature by performing a series of short-term leach tests. The leaching of Fâ from biotite structure strongly depends on its weathering stage. Results of this study suggest that high concentration of Fâ is leached from highly weathered biotite, compared to fresh biotite. Results of dissolution experiments confirm that the organic acids in soil promote the leaching of Fâ from biotite compared to inorganic acids. Citric acid which is a week organic acid enhances leaching of Fâ from biotite structure compared to strong inorganic acid HNO3, independent of the weathering stage of biotite. Strong positive correlation between K+ and Fe2+ with Fâ in biotite treated with citric acid suggests that Fâ readily leachs into the solution through an ionic exchange and complex formation. Organic acids involve sorption and complex formation processes leading to release of Fâ into the solution. Our studies suggest that in the presence of organic acids Fâ is leached readily into water percolating through the soil. Therefore, shallow groundwater replenished by the water table may achieve high Fâ concentrations by this leaching process
Valorisation du dioxyde de carbone (CO2) par le stockage de minéraux et la production d'hydrocarbures abiotiques
This study examined hydrogen production, CO2 storage and abiotic hydrocarbon generation duringgas-water-rock interactions by conducting hydrothermal experiments. The first part of this manuscriptpresents the simultaneous CO2 sequestration and hydrogen production by reacting New Caledonianmine tailings with CO2 saturated water at 473 K <T< 573 K and 15 MPa <PCO2< 30 MPa. The resultsshowed that the best conditions for both these reactions were 523 K <T<540 K at 30 MPa, capturing320.5 g of CO2 in the form of iron-rich magnesite ((Mg,Fe)CO3), and producing 0.57 g of H2 per 1 kgof mine tailings. In addition, considering the annual mine tailings production and the annual CO2emission in New Caledonia, the proposed method could potentially capture ~90 % of NewCaledoniaâs CO2 emissions. In addition, the H2 produced by this method could offset ~10 % of New-Caledoniaâs annual electrical consumption. Further investigation of secondary products and theirmineral-water interfaces at nanometer scale indicated that the reactions were taken place by dissolvingmine tailings followed by precipitation of iron rich magnesite, smectite group clay minerals(nontronite, vermiculite), traces of iron oxides and amorphous silica. Although, the phyllosilicates andamorphous silica could potentially act as passivating layers, slowing down the dissolution kinetics andconsequently limiting the CO2 storage and H2 production capacities, our experiments demonstratedthat the reactivity of New Caledonian mine tailings could also be lowered by the presence of glass.The second part of this manuscript presents the interaction of dissolved CO2 and H2 during thesynthesis of âabioticâ hydrocarbons, via Fischer-Tropsch type (FTT) synthesis in the presence of twopotential catalysts found in natural systems; sphalerite (ZnS) and marcasite (FeS2). The experimentswere conducted at 573 K and 30 MPa in gold capsules heated and pressurize in autoclaves. Hydrogennecessary for the reaction was provided by Fe2+ oxidation of minerals such as olivine(Mg1.80Fe0.2SiO4), fayalite (Fe2SiO4) and Fe-rich chlorite or chamosite (6Fe5Al(AlSi3)O10(OH)8).Methane (CH4) produced in our experiments was one order of magnitude higher than those reported inprevious studies when magnetite and iron oxide-chromite were used as catalysts for CH4 production,and in the same order of magnitude as pentlandite and Fe-Ni alloy catalysts. However, the smallconversion rates of inorganic carbon into organic carbon as well as the Schulz-Flory distribution ofC1-C4 alkanes demonstrated that sphalerite and marcasite do not explicitly catalyze the FTT synthesisof hydrocarbons under the conditions of these experiments.Cette Ă©tude a portĂ© sur la production dâhydrogĂšne, le stockage de CO2 et la productiondâhydrocarbures abiotiques dus aux interactions gaz-eau-roche lors dâexpĂ©riences hydrothermales. LapremiĂšre partie du manuscrit prĂ©sente la sĂ©questration de CO2 et la production de H2 simultanĂ©es lorsde la rĂ©action de rĂ©sidus miniers de Nouvelle-CalĂ©donie avec de lâeau saturĂ©e en CO2 Ă 473 K < T <573 K et 15 MPa < PCO2 < 30 MPa. Les rĂ©sultats montrent que les meilleures conditions pour cesdeux rĂ©actions sont 523 K < T < 540 K Ă 30 MPa, oĂč 320.5g de CO2 sont capturĂ©s sous forme demagnĂ©site riche en fer ((Mg,Fe)CO3), et oĂč 0.57g de H2 par kilogramme de rĂ©sidu minier sontproduits. En outre, en considĂ©rant la production annuelle de rĂ©sidus miniers et dâĂ©missions de CO2 enNouvelle-CalĂ©donie, la mĂ©thode proposĂ©e permettrait de potentiellement capturer ~90 % desĂ©missions totales de CO2. De plus, la production de H2 pourrait contribuer Ă hauteur de 10% de laconsommation Ă©nergĂ©tique annuelle. LâĂ©tude avancĂ©e des produits secondaires et leurs interfacesmineral-eau Ă lâĂ©chelle nanomĂ©trique nous indique que les rĂ©actions ont lieu en dissolvant les rĂ©sidusminiers puis en prĂ©cipitant de la magnĂ©site riche en fer, des minĂ©raux argileux smectites (nontronite,vermiculite), des traces dâoxydes de fer et de silice amorphe. Bien que les phyllosilicates et la siliceamorphe pourraient potentiellement agir comme des films de passivation rĂ©duisant la cinĂ©tique dedissolution et par consĂ©quence le stockage de CO2 et la production de H2, nos expĂ©riences montrentque la rĂ©activitĂ© des rĂ©sidus miniers de Nouvelle-CalĂ©donie peut ĂȘtre rĂ©duite par la prĂ©sence de verre.La seconde partie du manuscrit prĂ©sente lâinteraction entre le CO2 dissout et le H2 pendant la synthĂšsedâhydrocarbures abiotiques, notamment la rĂ©action de Fischer-Tropsch (FTT) en prĂ©sence de deuxcatalyseurs potentiels que lâon trouve dans les systĂšmes naturels : la sphalerite (ZnS) et la marcasite(FeS2). Les expĂ©riences ont Ă©tĂ© conduites Ă 573 K et 30 MPa dans des capsules en or placĂ©es dans unautoclave. LâhydrogĂšne nĂ©cessaire Ă la rĂ©action provient par lâoxydation-Fe2+ des minĂ©raux tels quelâolivine (Mg1.80Fe0.2SiO4), la fayalite (Fe2SiO4) et la chlorite riche en fer ou chamosite(6Fe5Al(AlSi3)O10(OH)8). La production de mĂ©thane (CH4) lors des expĂ©riences est dâun ordre degrandeur supĂ©rieur Ă ce qui a Ă©tĂ© rapportĂ© dans la littĂ©rature lorsque de la magnetite et de la chromiteont Ă©tĂ© utilisĂ©es comme catalyseur, et est du mĂȘme ordre de grandeur que lors de lâutilisation descatalyseurs pentlandite et alliages Fe-Ni. En revanche, le faible taux de conversion de carboneinorganique en carbone organique et la distribution Shulz-Flory des alcanes C1-C4 nous montrent quela sphalerite et la marcasite ne catalysent pas explicitement la rĂ©action FFT dâhydrocarbures dans lesconditions des expĂ©riences
Rutile solubility in hydrous rhyolite melts at 750-900°C and 2kbar, with application to titanium-in-quartz (TitaniQ) thermobarometry
New experimental data on TiO2 solubility in hydrous rhyolite melts : implications for titanium-in-quartz thermobarometry
Mineral carbonation of New Caledonian ultramafic mine slag : Effect of glass and secondary silicates on the carbonation yield
International audienceNew Caledonian nickel (Ni) mines produces âŒ12 million metric tons of mine slag every year, that are considered undesired and uneconomic waste materials. However, due to the high content of Mg2+ and Fe2+, these slags exhibit a potential of carbon dioxide (CO2) storage by ex-situ aqueous mineral carbonation. We conducted laboratory batch experiments at 200 °C/ 150 bar, 250 °C/ 300 bar, 300 °C/ 300 bar, in CO2-saturated water to better understand the slag dissolution, secondary mineral formation at the fluid-mineral interface, and the effect of the secondary silicates on the carbonation yield. The slag contains olivine (45 wt%) and glass (55 wt%). Olivine in the slag dissolves faster than glass, contributing to carbonate precipitation (Fe-rich magnesite) at 200 °C/150 bar. At 250 °C/ 300 bar, olivine is almost completely dissolved while glass dissolves only partially, both contributing to the highest recorded carbonation yields of the slag of 44 wt%. Although both olivine and glass are completely dissolved at 300 °C/ 300 bar, the carbonate yield drops at a value half of that at 250 °C/ 300 bar. This is due to formation of large quantity of Mg-bearing phyllosilicates that reduces the amount of Mg2+ available for carbonation. These results emphasize that increasing temperature above 250 °C would not increase the carbonate yield of New Caledonian mine slags. However, as glass only partially reacts at T < 250 °C, mobilizing Mg2+ in glass could potentially increase the carbonation yield, for example by adding suitable organic ligands. Mg-bearing phyllosilicates and amorphous silica that are formed in these experiments do not exhibit passivation properties, and therefore do not affect the carbonation rate
Formation of reduced carbon compounds using natural catalysts in hydrothermal experiments
Catalytic potential of natural minerals towards Fischer-Tropsch Type (FTT) synthesis of hydrocarbons
Revisiting clinico-epidemiological pattern of human rickettsial infections in the central region of Sri Lanka: a hospital based descriptive study
Abstract Background This study revisits the clinico-epidemiology and serological patterns of rickettsioses in the central region of Sri Lanka and highlights the need of advanced diagnostics for precise identification of species responsible for rickettsioses. Methods The patients treated for rickettsioses between November 2009 and October 2011 were recruited for the study from Teaching Hospital, Peradeniya. Clinical characteristics and serology results were used for diagnosis. Results Study included 210 patients (mean age 44 years ± 3.2) and of them 188 (90%) had positive IgG and/or IgM sero-reactivity for spotted fever group (SFG). Of them, 134 had IgG titre â„1/256 for SFG and presented with fever and skin rash. They also had headache [n = 119 (89%)], myalgia [n = 103 (77%)], arthralgia [n = 89 (66%)] of large joints, conjunctival injections [n = 83 (62%)], thrombocytopenia (n = 78.58%), anaemia (n = 14.10%), leukocytosis [n = 35 (26%)], leucopenia [n = 17 (13%)], elevated aspartate transaminase [n = 69 (52%)] and alanine transaminase [n = 73 (55%)]. Conclusions Predominance of SFG rickettsioses are reiterated, possibly transmitted by ticks. Joint disease is common with occasional fern leaf skin necrosis. Changing socio-economic conditions, vegetations, contact with domestic and wild animals, abundance of vectors would have contributed for emergence and sustenance of SFG in the region. Further research is needed to identify the causative agents and the mode of transmission