Leaching of fluoride from biotite mica in soil : implications for fluoride in shallow groundwater

Leaching of F− from biotite was investigated at room temperature by performing a series of short-term leach tests. The leaching of F− from biotite structure strongly depends on its weathering stage. Results of this study suggest that high concentration of F− 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 F− from biotite compared to inorganic acids. Citric acid which is a week organic acid enhances leaching of F− from biotite structure compared to strong inorganic acid HNO3, independent of the weathering stage of biotite. Strong positive correlation between K+ and Fe2+ with F− in biotite treated with citric acid suggests that F− readily leachs into the solution through an ionic exchange and complex formation. Organic acids involve sorption and complex formation processes leading to release of F− into the solution. Our studies suggest that in the presence of organic acids F− is leached readily into water percolating through the soil. Therefore, shallow groundwater replenished by the water table may achieve high F− 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 NewCaledonia’s CO2 emissions. In addition, the H2 produced by this method could offset ~10 % of New-Caledonia’s 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 “abiotic” 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 étude a porté sur la production d’hydrogène, le stockage de CO2 et la productiond’hydrocarbures abiotiques dus aux interactions gaz-eau-roche lors d’expériences hydrothermales. Lapremière partie du manuscrit présente la séquestration de CO2 et la production de H2 simultanées lorsde la réaction de résidus miniers de Nouvelle-Calédonie avec de l’eau saturée en CO2 à 473 K < T <573 K et 15 MPa < PCO2 < 30 MPa. Les résultats montrent que les meilleures conditions pour cesdeux réactions sont 523 K < T < 540 K à 30 MPa, où 320.5g de CO2 sont capturés sous forme demagnésite riche en fer ((Mg,Fe)CO3), et où 0.57g de H2 par kilogramme de résidu minier sontproduits. En outre, en considérant la production annuelle de résidus miniers et d’émissions de CO2 enNouvelle-Calédonie, la méthode proposée permettrait de potentiellement capturer ~90 % desémissions totales de CO2. De plus, la production de H2 pourrait contribuer à hauteur de 10% de laconsommation énergétique annuelle. L’étude avancée des produits secondaires et leurs interfacesmineral-eau à l’échelle nanométrique nous indique que les réactions ont lieu en dissolvant les résidusminiers puis en précipitant de la magnésite riche en fer, des minéraux argileux smectites (nontronite,vermiculite), des traces d’oxydes de fer et de silice amorphe. Bien que les phyllosilicates et la siliceamorphe pourraient potentiellement agir comme des films de passivation réduisant la cinétique dedissolution et par conséquence le stockage de CO2 et la production de H2, nos expériences montrentque la réactivité des résidus miniers de Nouvelle-Calédonie peut être réduite par la présence de verre.La seconde partie du manuscrit présente l’interaction entre le CO2 dissout et le H2 pendant la synthèsed’hydrocarbures abiotiques, notamment la réaction de Fischer-Tropsch (FTT) en présence de deuxcatalyseurs potentiels que l’on trouve dans les systèmes naturels : la sphalerite (ZnS) et la marcasite(FeS2). Les expériences ont été conduites à 573 K et 30 MPa dans des capsules en or placées dans unautoclave. L’hydrogène nécessaire à la réaction provient par l’oxydation-Fe2+ des minéraux tels quel’olivine (Mg1.80Fe0.2SiO4), la fayalite (Fe2SiO4) et la chlorite riche en fer ou chamosite(6Fe5Al(AlSi3)O10(OH)8). La production de méthane (CH4) lors des expériences est d’un ordre degrandeur supérieur à ce qui a été rapporté dans la littérature lorsque de la magnetite et de la chromiteont été utilisées comme catalyseur, et est du même ordre de grandeur que lors de l’utilisation 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 réaction FFT d’hydrocarbures dans lesconditions des expériences

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 ∼12 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

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 ≥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