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  • 1
    Language: English
    In: Journal of Hazardous Materials, March 21, Vol.285, p.464(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhazmat.2014.10.056 Byline: Stephan Kaufhold, Achim Walter Hassel, Daniel Sanders, Reiner Dohrmann Abstract: Corrosion at the bentonite iron interface proceeds unaerobically with formation of an 1:1 Fe silicate mineral. A series of exposure tests with different types of bentonites showed that Na-bentonites are slightly less corrosive than Ca-bentonites and highly charges smectites are less corrosive compared to low charged ones. The formation of a patina was observed in some cases and has to be investigated further. Display Omitted Author Affiliation: (a) BGR, Bundesanstalt fur Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover, Germany (b) Max-Planck-Institut fur Eisenforschung GmbH, Max-Planck-Stra[sz]e 1, D-40237 Dusseldorf, Germany (c) Institute for Chemical Technology of Inorganic Materials, Johannes Kepler University Linz, Altenberger Stra[sz]e 69, 4040 Linz, Austria (d) LBEG, Landesamt fur Bergbau, Energie und Geologie, Stilleweg 2, D-30655 Hannover, Germany Article History: Received 11 July 2014; Revised 9 September 2014; Accepted 29 October 2014
    Keywords: Radioactive Pollution ; Silicates ; Bentonite ; Corrosion (Chemistry) ; Smectite ; Radioactive Wastes ; Nuclear Environmental Management
    ISSN: 0304-3894
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Journal of Hazardous Materials, 21 March 2015, Vol.285, pp.464-473
    Description: Corrosion at the bentonite iron interface proceeds unaerobically with formation of an 1:1 Fe silicate mineral. A series of exposure tests with different types of bentonites showed that Na–bentonites are slightly less corrosive than Ca–bentonites and highly charges smectites are less corrosive compared to low charged ones. The formation of a patina was observed in some cases and has to be investigated further. Several countries favor the encapsulation of high-level radioactive waste (HLRW) in iron or steel canisters surrounded by highly compacted bentonite. In the present study the corrosion of iron in contact with different bentonites was investigated. The corrosion product was a 1:1 Fe layer silicate already described in literature (sometimes referred to as berthierine). Seven exposition test series (60 °C, 5 months) showed slightly less corrosion for the Na–bentonites compared to the Ca–bentonites. Two independent exposition tests with iron pellets and 38 different bentonites clearly proved the role of the layer charge density of the swelling clay minerals (smectites). Bentonites with high charged smectites are less corrosive than bentonites dominated by low charged ones. The type of counterion is additionally important because it determines the density of the gel and hence the solid/liquid ratio at the contact to the canister. The present study proves that the integrity of the multibarrier-system is seriously affected by the choice of the bentonite buffer encasing the metal canisters in most of the concepts. In some tests the formation of a patina was observed consisting of Fe–silicate. Up to now it is not clear why and how the patina formed. It, however, may be relevant as a corrosion inhibitor.
    Keywords: High-Level Radioactive Waste Canister ; Bentonite ; Iron ; Corrosion ; Bentonite–Iron-Interaction ; Engineering ; Law
    ISSN: 0304-3894
    E-ISSN: 1873-3336
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  • 3
    Language: English
    In: Geochimica et Cosmochimica Acta, 01 May 2016, Vol.180, pp.284-302
    Description: We evaluated the impact of nano-structural characteristics of allophanic compounds and Fe oxide speciation on the efficiency of organo-mineral interactions in an allophanic derived from volcanic ash (Eifel mountains, Germany). The samples selected for our work represented a gradient from: (i) a pure synthetic allophane and (ii) model organo-mineral mixtures to (iii) particle size fractions of the natural Andosol. We thus aimed to link the processes operating at the individual molecular scale to the phenomena active at the aggregate scale. For a non-destructive characterization of the samples, we applied Xe NMR spectroscopy of adsorbed Xe atoms (to identify the mineral nano-structure and surface acid centres), ESEM (verifying the nano-spherical structure of allophane), C CPMAS NMR (for the nature of the soil organic matter (SOM)), Fe Mössbauer spectroscopy (Fe oxide speciation), and N adsorption (contribution of micro- and mesoporosity). By using the atomic probe Xe, we obtained evidence for a mechanism of adsorption onto allophane requiring both the narrow pores (voids formed by the primary nano-spherules) and the acid centres located at the defect surfaces of the primary spherules. The validity of this coupled mechanism for the sorption of organic matter was confirmed by the concomitant blocking of acid centres ( Xe NMR data) and the decrease of the N -available pore volumes ( and ) in the model samples DOM/- and NOM/allophane (DOM = dissolved OM, NOM = natural OM). In the Andosol, the high resistance of SOM against oxidation (OC = 15–50%) was combined with preferential accumulation of certain organic compounds, e.g. potentially labile substrates such as carbohydrates, and the low molecular weight species such as amino acids. This feature was attributed to the peculiar microporous tortuous structure of allophane aggregates that likely impose certain criteria for the chemical nature and size of mineral-bound SOM. On the other hand, the revealed dominance of nanoparticulate Fe oxyhydroxides (57% ferrihydrite) and Fe-substituted allophane (supposedly formed due to co-precipitation of the Al, Si and Fe in the course of volcanic soil formation) may substantially contribute to the formation of highly resistant organo-mineral associations through the enhanced extent of reactive surface groups in nanoparticles, increased surface charge density and electron accepting properties of substituting Fe species that supposedly enhance the proportion of oxidised organic components.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 4
    Language: English
    In: Clays and Clay Minerals, 2010, Vol.58(1), pp.79-88
    Description: The aim of the present study was to find methodological tools to obtain reasonable results for exchangable Ca 2+ of gypsiferous bentonites. Cation exchange capacity (CEC) is an important property of clays. Numerous methods for calculating CEC and exchangeable cations exist; determination of exchangeable Ca 2+ fails, however, when gypsiferous clays are examined because gypsum is dissolved throughout the exchange experiment, which in turn increases measureable Ca 2+ concentrations. Several new methods (AgTU calcite , CoHex calcite , and Cu-trien 5×calcite ) have been developed to overcome a similar problem occurring with calcite by using exchange solutions saturated with respect to calcite prior to the experiment. In the present study these three solutions were also pre-treated with gypsum and labeled AgTU CcGp , CoHex CcGp , and Cu-trien 5×CcGp . The special solutions were applied first to a gypsum- and calcite-free bentonite with known reference values for exchangeable Ca 2+ . The resulting exchangeable Ca 2+ values obtained did not match with reference values. The solutions were then applied to natural calcareous and gypsiferous bentonites but only the proposed AgTU CcGp test method was successful. The performance of AgTU CcGp was relatively poor when applied to calcareous non-gypsiferous bentonites, the third group of test materials. Reasonable values for exchangeable Ca 2+ of gypsiferous clays were obtained using a combination of two separate results: (1) calcite saturation of exchange solution ( e.g. Cu-trien 5×calcite ) and (2) quantification of gypsum with suitable mineralogical methods. Result 1 eliminates errors caused by calcite dissolution though it is still incorrect because it contains significant amounts of Ca 2+ from gypsum dissolution. After proving that gypsum was completely dissolved during the exchange experiment, result 2 was used to subtract the theoretical Ca 2+ portion of gypsum from result 1. The initial concentration of gypsum of the samples studied was 〈1 wt.%, typical of many commercial bentonites. Using this combined procedure the sum of exchangeable cations is very close to the CEC, though it still exceeds the CEC by, on average, 3%, which is a satisfactory improvement. The resulting exchangeable Ca 2+ values can be considered as operationally correct using this approach. Ca 2+ saturation (Ca/CEC in %) of seven gypsiferous bentonites ranges from 1 to 69%.
    Keywords: AgTU Method ; Bentonites ; Gypsiferous Clays ; CEC ; CoHex Method ; Cu-trien Method ; Exchangeable Calcium
    ISSN: 0009-8604
    E-ISSN: 1552-8367
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  • 5
    Language: English
    In: Chemosphere, April 2016, Vol.149, pp.57-61
    Description: Bentonites, naturally occurring clays, are produced industrially because of their adsorbent capacity but little is known about their effects on human health. This manuscript reports on the effect of bentonites on cell growth behaviour. Bentonites collected from India (Bent-India), Hungary (Bent-Hungary), Argentina (Bent-Argentina), and Indonesia (Bent-Indonesia) were studied. All four bentonites were screened in-vitro against two human cancer cell lines [U251 (central nervous system, glioblastoma) and SKLU-1 (lung adenocarcinoma)] supplied by the National Cancer Institute (USA). Bentonites induced growth inhibition in the presence of U251 cells, and growth increment in the presence of SKLU-1 cells, showing that interactions between bentonite and cell surfaces were highly specific. The proliferation response for U251 cells was explained because clay surfaces controlled the levels of metabolic growth components, thereby inhibiting the development of high-grade gliomas, particularly primary glioblastomas. On the other hand, the proliferation response for SKLU-1 was explained by an exacerbated growth favoured by swelling, and concomitant accumulation of solutes, and their hydration and transformation clay-surface mediated reactions.
    Keywords: Cell Proliferation Response ; Swelling ; Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
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  • 6
    Language: English
    In: Clays and Clay Minerals, 2014, Vol.62(5), pp.357-373
    Description: Bentonites are candidate materials for high-level radioactive waste (HLRW) repositories and, therefore, are investigated with respect to long-term stability. In order to identify possible bentonite alteration processes, long-term in situ tests are conducted in rock laboratories. The prototype repository in situ experiment (PR) is one of the best examples of this kind of test due to the size of the installation as well as the duration. In the present study, chemical and mineralogical alteration processes of the bentonite MX 80 after an 8 y heating period were investigated. The water content of all samples increased following inflowing Na-Ca-Cl-type granitic groundwater causing cation exchange in the bentonite buffer materials. Exchangeable magnesium was desorbed in the buffer and MgO concentration increased at the bentonite-Cu canister interface; the Mg sink could not be detected, however. CaO also accumulated at this interface mainly as Ca carbonate and Ca sulfate. Cu corrosion products were identified at the bentonite-canister interface by chemical analysis, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDX), and differential thermal analysis. Up to 0.5 mm into the bentonites Cu could be detected by SEM-EDX. No cristobalite dissolution was observed in contrast to other in situ tests in which iron heaters were used. The corrosion products and the lubricant which was added during manufacturing of the bentonite blocks were mixed with the bentonite at the bentonite-canister interface. A quantitative measure of that mixture was the decrease in the cation exchange capacity (CEC). The CEC also reduced in all other samples, however, compared to the CECs of the reference samples, particularly in the warmer deposition hole 5 compared to the colder deposition hole 6. Overall, the PR in situ experiment proved that cation exchange reactions occurred in full-scale bentonite buffer experiments in all bentonite blocks but structural degradation of smectite could not be identified.
    Keywords: Bentonite Buffer ; CEC ; Exchangeable Cation Population ; Experiment ; MX 80 ; Prototype Repository Experiment
    ISSN: 0009-8604
    E-ISSN: 1552-8367
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  • 7
    Language: English
    In: Ore Geology Reviews, January 2016, Vol.72, pp.459-484
    Description: The kaolin-fan deposits under consideration are sedimentary in origin and they bridge the gap between residual kaolin deposits proximal to the fan apex in crystalline basement rocks and syn(dia)genetic sandstone-hosted kaolin deposits on the fan apron. The “kaolin ore beds” on the other hand, developed in an arenaceous braided-river drainage system (bed load 〉〉 suspended load deposits), reworking into secondary kaolin deposits that took place either intraformationally during the evolution of the kaolin fan deposits or epigenetically after unroofing of the kaolin deposits in high-sinuosity drainage systems passing, locally, into ephemeral lakes and mud flats (suspended load 〉 bed load deposits). The reference type for kaolin fan deposits has been studied in terrigeneous sediments which are largely mined at Hirschau–Schnaittenbach, along the Western edge of the Bohemian Massif, SE Germany. The fan deposits formed under alternating wet and dry subtropical climatic conditions during the early Triassic. Different intensities of uplift in the hinterland and the frequency of tectonic quiescence to tectonic pulse had a strong impact on the paleogradient, facies and hydrography of the kaolin fan deposits, resulting in the build-up of oxidized kaolin fans (OKF) and reduced kaolin fans (RKF). The OKF provide favorable conditions for the accumulation and preservation of kaolin deposits of economic potential, due to a low paleogradient and a continuous rate of uplift. The opposite is the case in the RKF that formed more proximal to the initial residual kaolin deposits and, more basinward, grade into sandstone-hosted (non)-sulfidic faciesbound Pb deposits that were targeted upon during exploration campaigns in the study area. The mineral association of the kaolin fan deposits has been categorized as follows: the allochthonous heavy minerals are zircon, tourmaline, apatite, monazite, xenotime, rutile, garnet, titaniferous magnetite, and ilmenite. They do not significantly vary between OKF and RKF. The autochthonous heavy minerals show strong contrasts in their heavy mineral suites. The RKF are enriched in sulfides and arsenides, which can be deleterious for the kaolin raw material and exclude its use for special final products (anatase, hematite, galena, sphalerite, marcasite, pyrite, bravoite (Ni pyrite), “limonite”, goethite, Ag–Cu–Ni–As sulfides, and barite). The OKF are rather poor in accessory minerals and contain anatase, hematite, and APS minerals. The latter are geo-acidometers (marker minerals for low pH) and considered as an ore guide to high-potential target areas for kaolin. The allochthonous light minerals quartz and K feldspar are common to both fan types and were only in parts affected by kaolinization, whereas plagioclase has been decomposed to completeness. Autochthonous light minerals quartz, chalcedony (carnelian), and calcite are exclusive to the RKF, where silcretes and calcretes evolved in those stratigraphic units which in the OKF only brought about Ca, Fe and Ti anomalies. The OKF have a significant edge over the RKF in terms of kaolin quality and kaolin exploitation (providing less mechanical wear on LHD [load–haul–dump machinery] machinery). Allochthonous phyllosilicates have a more widespread occurrence in the RKF with muscovite, biotite and chlorite most common in the lowermost kaolin beds. By quality there is not much difference among the autochthonous phyllosilicates of the OKF and RKF. Kaolinite-group minerals, illite, smectite, and an illite–smectite mixed-layer are present in both types, but kaolinite-group minerals prevail in the OKF, with a downward-increasing trend of dickite. By contrast the amount of smectite and smectite–illite mixed layers increases at the expense of kaolinite upward in the stratigraphy. The evolution of the kaolin fan deposits can be subdivided into six stages. Each stage is representative of a peculiar process which translates into concentration, preservation and destruction of kaolin: stage 1 weathering and the formation of a kaolin regolith (constructive), stage 2 transport, deposition synsedimentary to early-diagenetic kaolinization (constructive + preserving), stage 3 synsedimentary to early-diagenetic smectitization of kaolin (faciesbound Pb mineralization only in the RKF) (preserving + destructive), stage 4 late-diagenetic kaolinization and formation of dickite (preserving + constructive) (not in RKF), stage 5 epigenetic unconformity-related Cu–Ag–Ni–As–Ba mineralization (vaguely expressed in the OKF) (preserving), and stage 6 unroofing, erosion and redeposition of kaolin (only in the OKF) (destructive). During the study a PIMA device has proven in this type of kaolin deposit to be an efficacious tool for capturing digital data in the field of exploitation and exploration of industrial minerals for the identification and quantification of clay minerals (quality control).
    Keywords: Kaolin ; Fan Deposits ; Physical–Chemical Regime ; Sedimentological–Mineralogical Facies ; Mesozoic ; Se Germany ; Engineering ; Geology
    ISSN: 0169-1368
    E-ISSN: 1872-7360
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  • 8
    Language: English
    In: Journal of Hazardous Materials, 15 January 2018, Vol.342, pp.625-632
    Description: Antibiotic resistant bacteria persist throughout the world because they have evolved the ability to express various defense mechanisms to cope with antibiotics and the immune system; thus, low-cost strategies for the treatment of these bacteria are needed, such as the usage of environmental minerals. This paper reports the antimicrobial properties of a clay collected from Brunnenberg, Germany, that is composed of ferroan saponite with admixtures of quartz, feldspar and calcite as well as exposed or hidden (layered at inner regions) nano Fe(0). Based on the growth curves (log phase) of six antibiotic resistant bacteria (4 gram-negative and 2 gram-positive), we concluded that the clay acted as a bacteriostat; however, the clay was only active against the gram-negative bacteria (except for resilient ). The bacteriostatic mode of action was evidenced by the initial lack of Colony Forming Units on agar plates with growth registered afterward, certainly after 24 h, and can be explained because interactions between membrane lipopolysaccharides and the siloxane surfaces of the clay. Labile or bioavailable Fe in the clay (extracted by EDTA or DFO-B) induced the quantitative production of HO as well as oxidative stress, which, nevertheless, did not account for by its bacteriostatic activity.
    Keywords: Human Pathogens ; Low-Cost Remediation ; Engineering ; Law
    ISSN: 0304-3894
    E-ISSN: 1873-3336
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  • 9
    Language: English
    In: Journal of Hazardous Materials, 15 June 2014, Vol.274, pp.237-246
    Description: This paper reports that the main component of respirable volcanic ash, allophane, induces lipid peroxidation (LP), the oxidative degradation of lipids in cell membranes, and cytotoxicity in murin monocyle/macrophage cells. Naturally-occurring allophane collected from New Zealand, Japan, and Ecuador was studied. The quantification of LP was conducted using the Thiobarbituric Acid Reactive Substances (TBARS) assay. The cytotoxic effect was determined by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide colorimetric assay. Electron-Paramagnetic Resonance (EPR) determinations of naturally-occurring allophane confirmed the incorporation in the structure and clustering of structural Fe , and nucleation and growth of small-sized Fe (oxyhydr)oxide or gibbsite. LP induced by allophane varied with time, and solid concentration and composition, reaching 6.7 ± 0.2 nmol TBARS mg prot . LP was surface controlled but not restricted by structural or surface-bound Fe , because redox processes induced by soluble components other than perferryl iron. The reactivity of Fe soluble species stemming from surface-bound Fe or small-sized Fe refractory minerals in allophane surpassed that of structural Fe located in tetrahedral or octahedral sites of phyllosilicates or bulk iron oxides. Desferrioxamine B mesylate salt (DFOB) or ethylenediaminetetraacetic acid (EDTA) inhibited LP. EDTA acted as a more effective inhibitor, explained by multiple electron transfer pathways. Registered cell-viability values were as low as 68.5 ± 6.7%.
    Keywords: Naturally-Occurring Allophane ; Mineral Fe3+ ; Redox ; Oxidative Stress ; Engineering ; Law
    ISSN: 0304-3894
    E-ISSN: 1873-3336
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  • 10
    Language: English
    In: Journal of Soils and Sediments, 2012, Vol.12(1), pp.97-114
    Description: Byline: Tim Mansfeldt (1), Stephan Schuth (1,2), Werner Hausler (3), Friedrich E. Wagner (4), Stephan Kaufhold (5), Mark Overesch (1,6) Keywords: Iron oxides; Mossbauer spectroscopy; Redox processes; Soil; Stable iron isotopes Abstract: Purpose Properties of Fe oxides are poorly understood in soils with fluctuating water tables and variable redox conditions. The objective of this research was to (a) characterize the mineralogical composition of Fe oxides and (b) determine the relationship to the stable Fe isotope ratio in a soil with temporally and spatially sharp redox gradients. Materials and methods The lowland Gleysol (Petrogleyic) is in Northwest Germany and consists of oximorphic soil horizons (Ah 0--15, Bg 15--35, and CrBg 35--70 cm) developed from Holocene fluvial loam overlaying glaciofluvial sand with reductomorphic properties (2Cr horizon, +70 cm). Field measurements during the course of 28 months included the monitoring of groundwater table, soil redox potential, and analysis of the soil solutions. Solid Fe phases were studied by room temperature and cryogenic 57.sup.Fe Mossbauer spectroscopy, and stable Fe isotope compositions by multiple collector inductively coupled plasma mass spectrometry. Results and discussion The groundwater table ranged from -83 cm below to +8 cm above soil surface (median -27 cm). Permanent reducing conditions occurred in the 2Cr horizon with dissolved Fe concentrations of 44.8 mg L.sup.-1 (median). The duration of oxidizing conditions increased in the order CrBg 〈 Bg 〈 Ah. Total Fe increased from 50 (Ah) over 316 (Bg) up to 412 g kg.sup.-1 (CrBg) and was lowest in the 2Cr horizon (7 g kg.sup.-1). Ferrihydrite (51% of total Fe) was dominant over goethite (24%) in the Ah horizon. Conversely, nanogoethite dominated both the Bg (94%) and CrBg (86%) horizons. Iron in siderite amounted to 7% in the CrBg horizon. Iron isotope compositions yielded a range of [delta] 57.sup.Fe values from +0.29[per thousand] (Ah horizon) to -0.30[per thousand] (Bg horizon). In contrast to the overlying CrBg ([delta] 57.sup.Fe=-0.19[per thousand]) and Bg horizons, the 2Cr horizon is characterized by a relatively high [delta] 57.sup.Fe value of +0.22[per thousand]. Conclusions Lasting water saturation and frequent reducing conditions lead to the enrichment of goethite in subsoil. Once formed, goethite remains stable compared to ferrihydrite because it is less available for microbial mediated reductive dissolution. High [delta] 57.sup.Fe values in the topsoil primary result from fast ferrihydrite precipitation during aeration immediately after reducing conditions. In contrast, the low [delta] 57.sup.Fe values of the Fe-rich horizons (Bg, CrBg) promote adsorption of dissolved Fe with a light isotope composition onto goethite during capillary rise. The high [delta] 57.sup.Fe value of the Fe-poor subsoil (2Cr) is related to silicate-bound Fe rather than dissolution and precipitation of Fe oxides. Author Affiliation: (1) Department of Geosciences, Soil Geography/Soil Science, University of Cologne, Albertus-Magnus-Platz, 50923, Koln, Germany (2) Institute of Mineralogy, Leibniz University Hannover, Callinstrasse 3, 30167, Hannover, Germany (3) Soil Science, Technical University of Munich, Am Hochanger 2, 85354, Freising, Germany (4) Physics Department E15, Technical University of Munich, 85747, Garching, Germany (5) Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655, Hannover, Germany (6) M&O, Buro fur Geowissenschaften, Sudstrasse 26b, 49751, Sogel, Germany Article History: Registration Date: 16/07/2011 Received Date: 28/04/2011 Accepted Date: 16/07/2011 Online Date: 05/08/2011 Article note: Responsible editor: Michael Kersten
    Keywords: Iron oxides ; Mössbauer spectroscopy ; Redox processes ; Soil ; Stable iron isotopes
    ISSN: 1439-0108
    E-ISSN: 1614-7480
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