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Schweitenkirchen, Germany

Kaufhold S.,BGR Bundesanstalt fur Geowissenschaften und Rohstoffe | Dohrmann R.,BGR Bundesanstalt fur Geowissenschaften und Rohstoffe | Abidin Z.,Ehime University | Abidin Z.,University of Indonesia | And 5 more authors.
Applied Clay Science | Year: 2010

Worldwide F- contaminated groundwaters pose a serious health problem. For purification of these waters different adsorber materials are used such as activated aluminium oxide, iron oxyhydroxide (e.g. GEH®), or synthetic OH-Apatite (e.g. Fluorolith®). In some regions, however, inexpensive solutions are required motivating scientists to study the F- sorption of natural materials such as clays. The clay mineral allophane possesses a high affinity towards F-. In the present study different allophane samples are compared with other clay minerals as well as with Fluorolith®, a technically produced OH-apatite that is most commonly used in practice.Results obtained confirmed that allophane has the highest F- sorption capacity compared with kaolinite and goethite. The F- sorption capacity of some allophane samples is similar to the well-established F- adsorber material Fluorolith® and ranges from 3 to 5mg F-/g. Sorption depends on the experimental conditions, particularly the pH value (present study: 8-9). The different sorption capacity of the different allophanes could be explained by the amount of aluminol groups, which is independent of the specific surface area. The comparison of the fluoride uptake plots of allophanes with those of Fluorolith®, however, proved that Fluorolith® is particularly advantageous at low F- concentrations suggesting a higher affinity of the Fluorolith® surface towards F-. Sorption kinetics, however, were similar. Fluorolith® adsorbs F- by exchange of the structural anion OH-. The comparison of the uptake plots, however, suggests that different reactions have to be considered in the case of allophane. The sorption mechanism of fluoride on allophane could not be characterized further. © 2010 Elsevier B.V.

Gilg H.A.,TU Munich | Kruger Y.,University of Bern | Taubald H.,University of Tubingen | van den Kerkhof A.M.,University of Gottingen | And 2 more authors.
Mineralium Deposita | Year: 2014

Fluid inclusion studies in combination with hydrogen, oxygen and sulphur isotope data provide novel insights into the genesis of giant amethyst-bearing geodes in Early Cretaceous Paraná continental flood basalts at Amestita do Sul, Brazil. Monophase liquid inclusions in colourless quartz, amethyst, calcite, barite and gypsum were analysed by microthermometry after stimulating bubble nucleation using single femtosecond laser pulses. The salinity of the fluid inclusions was determined from ice-melting temperatures and a combination of prograde and retrograde homogenisation temperatures via the density maximum of the aqueous solutions. Four mineralisation stages are distinguished. In stage I, celadonite, chalcedony and pyrite formed under reducing conditions in a thermally stable environment. Low δ34SV-CDT values of pyrite (−25 to −32 ‰) suggest biogenic sulphate reduction by organotrophic bacteria. During the subsequent stages II (amethyst, goethite and anhydrite), III (early subhedral calcite) and IV (barite, late subhedral calcite and gypsum), the oxidation state of the fluid changed towards more oxidising conditions and microbial sulphate reduction ceased. Three distinct modes of fluid salinities around 5.3, 3.4 and 0.3 wt% NaCl-equivalent characterise the mineralisation stages II, III and IV, respectively. The salinity of the stage I fluid is unknown due to lack of fluid inclusions. Variation in homogenisation temperatures and in δ18O values of amethyst show evidence of repeated pulses of ascending hydrothermal fluids of up to 80–90 °C infiltrating a basaltic host rock of less than 45 °C. Colourless quartz and amethyst formed at temperatures between 40 and 80 °C, while the different calcite generations and late gypsum precipitated at temperatures below 45 °C. Calculated oxygen isotope composition of the amethyst-precipitating fluid in combination with δD values of amethyst-hosted fluid inclusions (−59 to −51 ‰) show a significant 18O-shift from the meteoric water line. This 18O-shift, high salinities of the fluid inclusions with chloride-sulphate composition, and high δ34S values of anhydrite and barite (7.5 to 9.9 ‰) suggest that sedimentary brines from deeper parts of the Guaraní aquifer system must have been responsible for the amethyst mineralisation. © 2014, Springer-Verlag Berlin Heidelberg.

Voerkelius S.,Hydroisotop GmbH
Analytical Chemistry | Year: 2011

We present a comprehensive chemical and mass spectrometric method to determine boron isotopic compositions of plant tissue. The method including dry ashing, a three-step ion chromatographic boron-matrix separation, and 11B/10B isotope ratio determinations using the Cs 2BO2 + graphite technique has been validated using certified reference and quality control materials. The developed method is capable to determine δ11B values in plant tissue down to boron concentrations of 1 mg/kg with an expanded uncertainty of ≥1.7‰ (k = 2). The determined δ11B values reveal an enormous isotopic range of boron in plant tissues covering three-quarters of the natural terrestrial occurring variation in the boron isotopic composition. As the local environment and anthropogenic activity mainly control the boron intake of plants, the boron isotopic composition of plants can be used for food provenance studies. © 2011 American Chemical Society.

Meier D.B.,University of Bern | Waber H.N.,University of Bern | Gimmi T.,University of Bern | Gimmi T.,Paul Scherrer Institute | And 2 more authors.
Journal of Contaminant Hydrology | Year: 2015

Geological site characterisation programmes typically rely on drill cores for direct information on subsurface rocks. However, porosity, transport properties and porewater composition measured on drill cores can deviate from in-situ values due to two main artefacts caused by drilling and sample recovery: (1) mechanical disruption that increases porosity and (2) contamination of the porewater by drilling fluid. We investigated the effect and magnitude of these perturbations on large drill core samples (12-20 cm long, 5 cm diameter) of high-grade, granitic gneisses obtained from 350 to 600 m depth in a borehole on Olkiluoto Island (SW Finland). The drilling fluid was traced with sodium-iodide. By combining out-diffusion experiments, gravimetry, UV-microscopy and iodide mass balance calculations, we successfully quantified the magnitudes of the artefacts: 2-6% increase in porosity relative to the bulk connected porosity and 0.9 to 8.9 vol.% contamination by drilling fluid. The spatial distribution of the drilling-induced perturbations was revealed by numerical simulations of 2D diffusion matched to the experimental data. This showed that the rims of the samples have a mechanically disrupted zone 0.04 to 0.22 cm wide, characterised by faster transport properties compared to the undisturbed centre (1.8 to 7.7 times higher pore diffusion coefficient). Chemical contamination was shown to affect an even wider zone in all samples, ranging from 0.15 to 0.60 cm, in which iodide enrichment was up to 180 mg/kgwater, compared to 0.5 mg/kgwater in the uncontaminated centre. For all samples in the present case study, it turned out that the magnitude of the artefacts caused by drilling and sample recovery is so small that no correction is required for their effects. Therefore, the standard laboratory measurements of porosity, transport properties and porewater composition can be taken as valid in-situ estimates. However, it is clear that the magnitudes strongly depend on site- and drilling-specific factors and therefore our results cannot be transferred simply to other locations. We recommend the approach presented in this study as a route to obtain reliable values in future drilling campaigns aimed at characterising in-situ bedrock properties. © 2015 Elsevier B.V.

Alt-Epping P.,University of Bern | Waber H.N.,University of Bern | Diamond L.W.,University of Bern | Eichinger L.,Hydroisotop GmbH
Geothermics | Year: 2013

Mineral scaling, corrosion and chemical reactions between the re-injected fluid and the aquifer rock affect the long-term exploitation of deep geothermal systems. We use numerical models patterned after the geothermal system at Bad Blumau, Austria, to track the passage of the production fluid through the system. As model input we use pressure, temperature, and fluid composition data collected at the ground surface, as well as evidence for CO2 gas exsolution within the production well. From these constraints we infer the chemical conditions in the reservoir, assess the geochemical implications of the extraction of heat and CO2(g) at the surface, examine the consequences of fluid re-injection into the reservoir, and identify geochemical indicators of incipient corrosion. Exsolution and the subsequent extraction of CO2(g) from the fluid decreases the total CO2, increases the pH and, if not suppressed by adding chemical inhibitors, causes precipitation of carbonate minerals. Calculations show that without the inhibition of Ca-bearing carbonates, the production well could be clogged within a few days. The compositional changes caused by CO2 extraction and the lower temperature of the reinjected fluid trigger disequilibrium reactions at the base of the injection well, potentially affecting the injectivity of the system. Owing to the high redox buffering capacity of the fluid, indicators for incipient corrosion include an increase in the fraction of pyrite in the production well and increase in Fe-oxides/hydroxides near the surface under higher pH and lower temperature conditions. © 2012 Elsevier Ltd.

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