Bentonite Deposits Research Articles

Characterization of Romanian Bentonitic Clays for the Removal of Dyes from Wastewater

ABSTRACTBentonites from Oraşul Nou (Satu Mare County), Petreşti (Cluj County), Valea Chioarului (Maramureş County), and Gurasada (Hunedoara County), Transylvania, Romania, were characterized and tested as adsorbents for the removal of toluidine blue, malachite green, and Congo red from aqueous solution. The clay materials were characterized using X-ray diffraction, scanning electron microscopy-energy-dispersive X-ray spectroscopy, specific surface area using the Brunauer–Emmett–Teller method, and infrared spectroscopy. Physicochemical and mineralogical analyses of the samples indicated that all included montmorillonite as their main constituent and that important modifications of their properties occurred upon treatment. Each bentonite was subjected to size-fractionation, ionic exchange with tetra-n-butylammonium bromide (organoclay), and Al-pillaring. Adsorption was conducted using batch conditions for 4 h using 0.1 g adsorbent and 40 mL of 100 mg/L dye solution at 20 ± 2°C and 25 rpm with a three-dimensional shaker. The most efficient bentonite deposits were from Oraşul Nou. The most suitable modified samples were treated by size-fractionation.

Evidence of montmorillonite/Fe-rich smectite transformation in the Morrón de Mateo bentonite deposit (Spain): Implications for the clayey barrier behaviour

The Morrón de Mateo bentonite deposit (Cabo de Gata region, Spain) has been studied as a natural analogue of the thermal and geochemical effects on the clayey barrier in a deep geological repository of high level radioactive wastes. This deposit was intruded by a volcanic dome inducing an increase of temperature and supplying Fe–Mg-rich solutions, which were responsible for the alteration of the previously bentonitised pyroclastic materials (white tuff formation). The textural, mineralogical and crystallochemical features of the smectites located within the vicinity and away from the dome have been studied in order to elucidate the intrusion effects on these smectites. The results obtained show that distal smectites are Al-montmorillonites, similar to those from other bentonite deposits in the Cabo de Gata region; whereas proximal smectites are a mixture of Al-montmorillonites, Fe-rich montmorillonites and beidellites, and intermediate smectites between beidellite and Fe-rich-saponite. The textural relationships between these smectites indicate that smectites with intermediate composition come from the transformation of Al-montmorillonite, through gradual steps, consisting of increasingly Mg and Fe-rich smectites. This transformation process is confirmed when the structural formulae of proximal smectites are plotted on the MgVIvs (Al+Fe3+)VI diagram. Thus, a gradual transition from dioctahedral smectites to smectites with an intermediate chemical composition is observed, which tend toward trioctahedral smectites. These observations suggest that the transformation of dioctahedral smectites into an intermediate term between di- and trioctahedral Fe-rich smectites could be originated under natural conditions. This transformation can be considered as an analogue process to that expected in the bentonite barrier from a deep geological repository of radioactive wastes whether the two following conditions would occur: i) an increase of temperature due to the radioactive decay of the fission products, and ii) a supply of Fe as result of the canister corrosion under intermediate redox conditions. Furthermore, similar results were obtained in laboratory experiments focused on the Fe/Al-smectite interaction processes, related to the durability of the clayey engineered barrier.

Characteristics and genesis of montmorilonitic claystone from Bandung area, Wonosegoro, Boyolali, Central Java, Indonesia

The Bandung bentonite deposit is located in Wonosegoro District, Boyolali Regence, Central Java. Characteristics of bentonite in this area are very important due to increase demand on bentonite in the industry. Several methods are used to characterize the bentonite in this area, such as PLM (polarizing light microscope), X-Ray Diffraction and Scanning Electron Microscope combined with EDX measurements. The montmorilonitic claystone belongs to Kerek Formation from Banyuurip Member. This deposit consists of mainly montmorilonitic claystone interbedded with tuffaceous sandstone. Petrographical analysis shows that montmorilonitic claystone consists of mostly clay minerals with small amount of calcite, volcanic glass, feldspar, quartz, and opaque minerals. The clay minerals are likely as alteration product of volcanic glass. The oriented XRD analyses show that the clay samples consist of Ca-montmorilonite, illite, and kaolinite. Physico-chemical analyses of montmorilonitic claystone display that the initial CEC (cation exchange capacity) is 20 mgrek.Na2O/200gr (54 mg.Na2O/100gr) and low swelling ability for about 2 times of its initial volume. Based on its mineralogical association, textures, and stratigraphic position, the montmorilonite is formed from devitivication of volcanic glass in a diagenetic environment with over 2 km thicks of overburden. Keywords: Bentonite, montmorillonitic claystone, devitrivication, diagenesis, montmorillonite

THE RESULTS OF PHYSICO-CHEMICAL STUDIES OF BENTONITE OF DASHUKOVSKІУ FIELD

Thus, the basic physical and chemical properties ( moisture content (57,19 %), unit weight (1,31), shear stress (821,59 Pa), stickiness (1839,81 Pa), debris particles with a diameter of more than 250 mkm (0,34 %), specific heat (2,75 kG/(kg · K)) bentonite deposits Dashukovskoho Cherkasy region meets the eligibility criteria of the Therapeutic muds (peloids). The chemical composition of the aqueous extract of clay deposits Dashukovskoho refers to magnesium sulphate-bicarbonate-calcium-sodium type or complex cation composition with mineralization of 0,26 g/dm3. pH of the extract of clay is 7,95 m. pH is characterized by slightly alkaline reaction. Positive values oxidation -reduction potential of the extract of clay (+ 465 mV) indicate the presence of oxidative processes. This is because the clay extraction in the preparation of the latter was in contact with oxygen. It should be noted that the calculation of the structural formulabentonite is great information because it allows to introduce the character of isomorphic substitutions in the structure, efficiently detect the composition of exchange cations, which makes it possible to predict the behavior of the sample during its processing technology.

The Early Miocene “Bisciaro volcaniclastic event” (northern Apennines, Italy): a key study for the geodynamic evolution of the central-western Mediterranean

The Early Miocene Bisciaro Fm., a marly limestone succession cropping out widely in the Umbria–Romagna–Marche Apennines, is characterized by a high amount of volcaniclastic content, characterizing this unit as a peculiar event of the Adria Plate margin. Because of this volcaniclastic event, also recognizable in different sectors of the central-western Mediterranean chains, this formation is proposed as a “marker” for the geodynamic evolution of the area. In the Bisciaro Fm., the volcaniclastic supply starts with the “Raffaello” bed (Earliest Aquitanian) that marks the base of the formation and ends in the lower portion of the Schlier Fm. (Late Burdigalian–Langhian p.p.). Forty-one studied successions allowed the recognition of three main petrofacies: (1) Pyroclastic Deposits (volcanic materials more than 90 %) including the sub-petrofacies 1A, Vitroclastic/crystallo-vitroclastic tuffs; 1B, Bentonitic deposits; and 1C, Ocraceous and blackish layers; (2) Resedimented Syn-Eruptive Volcanogenic Deposits (volcanic material 30–90 %) including the sub-petrofacies 2A, High-density volcanogenic turbidites; 2B, Low-density volcanogenic turbidites; 2C, Crystal-rich volcanogenic deposits; and 2D, Glauconitic-rich volcaniclastites; (3) Mixing of Volcaniclastic Sediments with Marine Deposits (volcanic material 5–30 %, mixed with marine sediments: marls, calcareous marls, and marly limestones). Coeval volcaniclastic deposits recognizable in different tectonic units of the Apennines, Maghrebian, and Betic Chains show petrofacies and chemical–geochemical features related to a similar calc-alkaline magmatism. The characterization of this event led to the hypothesis of a co-genetic relationship between volcanic activity centres (primary volcanic systems) and depositional basins (depositional processes) in the Early Miocene palaeogeographic and palaeotectonic evolution of the central-western Mediterranean region. The results support the proposal of a geodynamic model of this area that considers previously proposed interpretations.

Месторождения бентонитов Республики Татарстан: геология и генезис, направления использования сырья

Месторождения бентонитов Республики Татарстан: геология и генезис, направления использования сырья

Characterization of natural organic matter in bentonite clays for potential use in deep geological repositories for used nuclear fuel

The Nuclear Waste Management Organization (NWMO) is developing a Deep Geological Repository (DGR) to contain and isolate used nuclear fuel in a suitable rock formation at a depth of approximately 500m. The design concept employs a multibarrier system, including the use of copper-coated used fuel containers, surrounded by a low-permeability, swelling clay buffer material within a low permeability, stable host rock environment. The natural organic matter (NOM) composition of the bentonite clays being considered for the buffer material is largely uncharacterized at the molecular-level. To gain a better understanding of the NOM in target clays from Wyoming and Saskatchewan, molecular-level methods (biomarker analysis, solid-state 13C NMR and solution-state 1H nuclear magnetic resonance (NMR)) were used to elucidate the structure and sources of NOM. Organic carbon content in three commercially available bentonites analyzed was low (0.11–0.41%). The aliphatic lipid distribution of the clay samples analyzed showed a predominance of higher concentration of lipids from vascular plants and low concentrations of lipids consistent with microbial origin. The lignin phenol vanillyl acid to aldehyde ratio (Ad/Al) for the National sample indicated an advanced state of lignin oxidation and NOM diagenesis. The 13C NMR spectra were dominated by signals in the aromatic and aliphatic regions. The ratio of alkyl/O-alkyl carbon ranged from 7.6 to 9.7, indicating that the NOM has undergone advanced diagenetic alteration. The absence lignin-derived phenols commonly observed in CuO oxidation extracts from contemporary soils and sediments as well as the lack of amino acids suggests that the material corresponding to the aromatic signal is not composed of lignin or proteins but may be derived from another source such as black carbon or some other non-extractable aromatic-rich NOM. The aliphatic signal appears to correspond to long-chain compounds with little side branching based on the results of the one-dimensional (1D) and two-dimensional (2D) solution-state 1H NMR analyses. Overall, the organic geochemical analyses suggest that the NOM is composed mainly of plant-derived waxes and highly aromatic carbon with low contributions from small molecules. The compounds identified by the molecular-level analysis of NOM in the clay samples are hypothesized to be recalcitrant but future studies should examine if these compounds may serve as a microbial substrate to further test the observations of this study. Furthermore, our study suggests that the NOM has undergone diagenesis and that marine NOM signatures are no longer recognizable or detectable. As such, future work may also examine the diagenesis of these deposits to further understand the NOM geochemistry and paleoenvironmental conditions in bentonite deposits.

Tephrochronology and geochemistry of Eocene and Oligocene volcanic ashes of east and central Texas

New single-crystal sanidine 40 Ar/ 39 Ar dates of 12 middle Eocene to Oligocene rhyolitic volcanic ash beds of the Texas coastal plains range from 30.64 ± 0.03 Ma (lower Catahoula Formation) to 41.841 ± 0.016 Ma (lower Crockett Formation). These dates are from Texas coastal plains strata in the Crockett marine transgression and the Yegua and Jackson depositional wedges. Radiometric dating of sanidine and electron microprobe analysis of volcanic apatite phenocrysts validate previous regional correlation of the Upper Alabama Ferry volcanic ash from Brazos County to Houston County, Texas, and provide support for correlation of this bed with the St. Johns bentonite deposit in Louisiana. Middle Eocene ash beds are distinguished by differences in apatite phenocryst composition. The wide distribution of the thick Alabama Ferry volcanic ashes points to an early age (41.841 ± 0.016 Ma) for the start of major explosive rhyolitic volcanism in western North America. Volcanic ash bed samples have subalkaline rhyolite composition with geochemical characteristics consistent with derivation from volcanic arc rocks. Trace-element data show a temporal change in volcanic ashes: Middle Eocene ashes are depleted in heavy rare earth elements compared to late Eocene and Oligocene units. This change in ash composition coincides with the time of transition from subduction compression to arc-rifting on the western margin of Mexico, and compositional data are consistent with the Sierra Madre Occidental being the source for the volcanic ash. Volcanic units of the eastern portion of the Trans-Pecos of Texas and Mogollon-Datil area of New Mexico overlap temporally, but geochemical characteristics and K/Ca ratios in sanidine indicate they are geochemically unlikely to be sources for the Texas coastal plains middle Eocene to Oligocene volcanic ash beds.

Prospecting for clay minerals within volcanic successions: Application of electrical resistivity tomography to characterise bentonite deposits in northern Sardinia (Italy)

Electrical resistivity tomography (ERT) is applied to prospect for and characterise a bentonitic clay deposit in northern Sardinia. Sardinian bentonites derived from the hydrothermal alteration of thick successions of pyroclastic flows and epiclastites are associated with the Oligo-Miocene calc-alkaline volcanic cycle. The alteration of these rocks is generally controlled by faults that control the local circulation of hydrothermal fluids. Two-dimensional ERT investigations were performed close to a faulted area to define the location, thickness and lateral continuity of the clayey body, and determine how it relates to faulting and stratigraphy. A line-based three-dimensional ERT data acquisition was carried out in a selected area to estimate the available clay reserves. The reliability of these resistivity models was assessed by comparison with local borehole data. Finally, the interpretation of the ERT results was optimised through synthetic modelling of the electrical resistivity imaging technique. The results define the extent and geometry of the bentonitic deposit with good accuracy and outline the scenarios where the ERT method may provide optimal results when prospecting for clay deposits.

New results on ground deformation in the Upper Silesian Coal Basin (southern Poland) obtained during the DORIS Project (EU-FP 7)

This paper presents application of satellite interferometric methods (persistent scatterer interferometric synthetic aperture radar (PSInSAR™) and differential interferometric synthetic aperture radar (DInSAR)) for observation of ground deformation in the Upper Silesian Coal Basin (USCB) in Southern Poland. The presented results were obtained during the DORIS project (EC FP 7, Grant Agreement n. 242212, www.doris-project.eu). Several InSAR datasets for this area were analysed. Most of them were processed by Tele-Rilevamento Europa - T.R.E. s.r.l. Italy. Datasets came from different SAR satellites (ERS 1 and 2, Envisat, ALOS- PALSAR and TerraSAR-X) and cover three different SAR bands (L, C and X). They were processed using both InSAR techniques: DInSAR, where deformations are presented as interferometric fringes on the raster image, and PSInSAR, where motion is indentified on irregular set of persistent scatterer (PS) points. Archival data from the C-band European Space Agency satellites ERS and ENVISAT provided information about ground movement since 1992 until 2010 in two separate datasets (1992–2000 and 2003–2010). Two coal mines were selected as examples of ground motion within inactive mining areas: Sosnowiec and Saturn, where mining ceased in 1995 and 1997, respectively. Despite well pumping after closure of the mines, groundwater rose several dozen meters, returning to its natural horizon. Small surface uplift clearly indicated on satellite interferometric data is related to high permeability of the hydrogeological subregion and insufficient water withdrawal from abandoned mines. The older 1992–2000 PSInSAR dataset indicates values of ground motion ranging from –40.0 to 0.0 mm. The newer 2003–2010 dataset shows values ranging from –2.0 to +7.0 mm. This means that during this period of time subsidence was less and uplift greater in comparison to the older dataset. This is even more evident in the time series of randomly selected PS points from both coal mines. The presence of bentonite deposits in the Saturn coal mine can also have influence on the ground surface uplift. Analysis of interferometric L and X-band data in Upper Silesia has enabled observation and monitoring of the underground mining front for several months. It was indicated by the example from the Halemba–Wirek coal mine. Analysis of the TerraSAR–X dataset processed by SqueeSAR algorithms proved to be the most effective for this purpose. X-band persistent scatterer interferometry (PSI) time series can help to indentify small seemingly negligible movements and are successfully supplemented by fringes when displacement becomes significant. Differential interferograms from the L-band dataset detect similar displacement values but, thanks to longer wavelength, are characterized by better coherence, especially in the middle of the subsidence trough. Results on ground deformation proved that ground motion above abandoned mines continues long after their closure. Therefore, existing regulations stating that abandoned mines are considered fully safe five years after mine closure should change. Moreover, it should be emphasised that construction in these areas should be avoided due to existing potential risks.

Characteristics, modification and environmental application of Yemen’s natural bentonite

The bentonite deposit of Lahij Province, Yemen, has very promising commercial applications due to its mineralogy and physical and chemical properties. It was examined to determine its mineralogical composition, chemical and physical properties of the bentonite deposit, purity and sodium-exchanged bentonite. Modified bentonite was synthesized by exchanging cetyltrimethylammonium cations for inorganic ions on the bentonite and its adsorption properties for ammonium were characterized in batch experiments. Analytical methods were carried out to study the bentonite comprising X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy, chemical analysis and kinetic and isotherm models were also tested. The results have shown that the purification of bentonite resulted in a bentonite fractions of the total sample composed of montmorillonite and <5 % quartz. The XRD data showed that the interlayer spacing (d 001) of bentonite decreased from 15.3 to 12.5 A and then increased to 19.7 A. Moreover, high cation exchange capacity, good water absorption and high swelling capacity were also obtained. The results have shown that the modified bentonite was more effective than the natural bentonite for ammonium removal. In addition to that, pseudo-second-order kinetic model, Freundlich and the Langmuir models described the adsorption kinetics and isotherm well. It was concluded that Yemen (Alaslef) bentonite can be potential adsorbents for ammonium removal.

Geology and geochemistry of Kurkur bentonites, southern Egypt: provenance, depositional environment, and compositional implication of Paleocene–Eocene thermal maximum

A large lower Eocene bentonite deposit at the top of Sinn El-Kaddab plateau, southern Egypt, is investigated. It forms isolated anticlinal hills as mesa and cuesta geomorphic units. The Sinn El-Kaddab plateau (497 m above sea level) with Gebel Abyad in northern Sudan represent the most southern margin of Tethys realm in East Africa. Clay and silt fractions constitute up to 95 % of the bentonite and calcium montmorillonite is the predominant phase (70–87 %). These sediments were deposited during the Paleocene–Eocene Thermal Maximum (PETM) event. Grain-size distribution in conjunction with their geologic setting argues in favor of a low energy deep hemipelagic, restricted basin within the outer shelf zone. They suggest sporadic deposition in a basin characterized by relief oscillation, in response to continuous tectonic uplifting. The sediments of the peripheral parts of the basin are more calcareous and were deposited in an arid climatic condition. Calcium montmorillonite was deposited in subtropical warm climate, with alternating wet and dry seasons. Compositionally, the bentonite shales are basic to intermediate and exhibit a rather limited range of K2O/Na2O and SiO2/Al2O3 ratios. They suggest mature polycyclic siliciclastics as the main provenance and within-plate alkali basalts as a main igneous precursor. They are the product of intensive physical weathering process in response to combined effects of both tectonic disturbance and prevailed climatic conditions during the PETM event. Geochemically, they are interpreted in terms of mixing of two end-members: pure clastic terrigenous component (inherited from the source area) and carbonate-rich matrix.

Field occurrence and properties of Cretaceous to Paleogene bentonite deposits in U.S.A.

Field occurrence and properties of Cretaceous to Paleogene bentonite deposits in U.S.A.

Smectites in Bentonite Deposits, Black Hills, Wyoming

Smectites in Bentonite Deposits, Black Hills, Wyoming

A Method for Determining Thermal History of Main Bentonite Deposits in the Annaka-Tomioka Area

A Method for Determining Thermal History of Main Bentonite Deposits in the Annaka-Tomioka Area

Study on Sodium Modification of Inferior Ca-Based Bentonite by Suspension Method

Hunyuan Ca-based bentonite is one of large-type bentonite deposits in China, the reserve of which is more than 0.15 billion tons. However, they are not completely utilized in the pellet production. Process mineralogy investigation shows that the bentonite is a kind of typical Ca-bentonite (Ca-Bent). The sodium modification of the sample is studied by suspension method in this study. Results present the alkali coefficient K of modified Na-bentonite that is increased from 0.34 to 1.33, and the 2HWA, dilation, and colloid index are, respectively, increased to 601%, 32.4 mL/g and 87.6 mL/(3 g) under optimal conditions of Na2CO3 dosage 3.0%, pulp density 20%, sodium temperature 55°C, and sodium time 0.5 h. The XRD patterns show that d(001) of the sample bentonite is reduced from 1.5539 nm down to 1.2467 nm, and 2θ(001) of the sample bentonite is increased from 5.6875° to 7.0907°, indicating that the sample Ca-Bent is effectively modified into Na-Bent.

Aflatoxin Toxicity Reduction in Feed by Enhanced Binding to Surface-Modified Clay Additives

Animal feeding studies have demonstrated that clay additives, such as bentonites, can bind aflatoxins in ingested feed and reduce or eliminate the toxicity. Bentonite deposits are found throughout the world and mostly consist of expandable smectite minerals, such as montmorillonite. The surfaces of smectite minerals can be treated with organic compounds to create surface-modified clays that more readily bind some contaminants than the untreated clay. Montmorillonites treated with organic cations, such as hexadecyltrimethylammonium (HDTMA) and phenyltrimethylammonium (PTMA), more effectively remove organic contaminants, such as benzene and toluene, from water than untreated clay. Similarly, montmorillonite treated with PTMA (Kd = 24,100) retained more aflatoxin B1 (AfB1) from aqueous corn flour than untreated montmorillonite (Kd = 944). Feed additives that reduced aflatoxin toxicity in animal feeding studies adsorbed more AfB1 from aqueous corn flour than feed additives that were less effective. The organic cations HDTMA and PTMA are considered toxic and would not be suitable for clay additives used in feed or food, but other non-toxic or nutrient compounds can be used to prepare surface-modified clays. Montmorillonite (SWy) treated with choline (Kd = 13,800) and carnitine (Kd = 3960) adsorbed much more AfB1 from aqueous corn flour than the untreated clay (Kd = 944). A choline-treated clay prepared from a reduced-charge, high-charge montmorillonite (Kd = 20,100) adsorbed more AfB1 than the choline-treated high-charge montmorillonite (Kd = 1340) or the untreated montmorillonite (Kd = 293). Surface-modified clay additives prepared using low-charge smectites and nutrient or non-toxic organic compounds might be used to more effectively bind aflatoxins in contaminated feed or food and prevent toxicity.

Occurrence of Fe–Mg-rich smectites and corrensite in the Morrón de Mateo bentonite deposit (Cabo de Gata region, Spain): A natural analogue of the bentonite barrier in a radwaste repository

► A hydrothermal process transformed Fe–Mg smectites into corrensite. ► This transformation was favoured by the intrusion of the Morrón de Mateo dome. ► The intrusion caused a temperature increased and a supply of Fe–Mg rich solutions. ► The system can be a good natural analogue of bentonite barrier in a radwaste disposal. ► Experimental studies of stability of bentonite are in agreement with the results. The Morrón de Mateo bentonite deposit is being studied as a natural analogue of the thermal and geochemical effects on a bentonite barrier in a deep geological repository of high level radioactive wastes. This bentonite deposit and its host rocks were intruded by a rhyodacitic volcanic dome that induced a hydrothermal metasomatic process affecting the biocalcarenite beds close to the dome. In this work, the mineralogical and chemical features of the clay minerals of the hydrothermally altered pyroclastic (white tuffs) and epiclastic rocks (mass flow), located in the NE sector of the Morrón de Mateo deposit are described. White tuffs have a high content of phyllosilicates, mainly composed of dioctahedral smectites, while mass flow have a higher proportion of inherited minerals, the neoformed phyllosilicates are dioctahedral smectites and an interlayer chlorite/smectite mineral of corrensite type. The chemical composition of smectites reflects the different nature of the parent rocks, in such a way that smectites from white tuffs have a quite homogeneous chemical composition and their structural formulae correspond to montmorillonite type, while smectites from mass flow show more chemical variability, higher Fe and Mg contents and a mean structural formulae corresponding to Fe–Mg-rich beidellite and/or to an intermediate smectite member between beidellite and saponite. In addition, chemical composition and textural features of corrensite-like clay minerals in relation to Fe–Mg-rich smectites in the samples have also been studied, suggesting that the former seems to be formed from Fe–Mg-rich smectites. The presence of corrensite in the epiclastic rocks suggests that in the Morrón de Mateo area a hydrothermal alteration process occurred after bentonite formation, which transformed Fe–Mg-rich smectites into corrensite. This transformation was probably favoured by the intrusion of the Morrón de Mateo volcanic dome, which produced a temperature increase in the geological media and a supply of Fe–Mg-rich solutions. These physicochemical conditions were also responsible for the metasomatic transformations observed in the biocalcarenite beds located on the top of the bentonite deposit. All these data suggest that the Morrón de Mateo natural system could be a good natural analogue of both thermal and chemical effects on a bentonite barrier related to the radioactive decay of fission products and the interaction between the corrosion products of steel over-packs and the bentonite. These circumstances would favour the transformation of the candidate Al-rich smectites into Fe–Mg-rich smectites and corrensite, as steps prior to formation of chlorite. In this case, all the physicochemical and mechanical properties of Al-rich smectites would disappear and the clayey barrier would fail.

Utilization of Slovak bentonites in deposition of high-level radioactive waste and spent nuclear fuel

The basic strategic aims in the field of managing high-level radioactive waste and liquidation of nuclear power plants are all contained in the Energy policy of the Slovak Republic. Its aim is to resolve the concept of the backside of the nuclear energetics fuel cycle—long-term deposition of high-level radioactive waste and spent nuclear fuel (SNF). The most important form of high-level radioactive waste and SNF long-term deposition is their deposition in deep geological formations created by natural as well as engineering barriers used to isolate the long-lived radionuclides from the biosphere. The basic components of these barriers are clays, of which bentonite is generally referred to as the most suitable clay material. There are a few significant bentonite deposits in the Slovak Republic: Jelsový potok, Kopernica, Lastovce, Lieskovec, Dolna Ves. The review article summarizes the information on geotechnical properties of Slovak bentonites published up-to-date, which is inevitable to know for the intention of their use. It highlights the advantages and shows drawbacks of five Slovak deposits. It suggests further research direction, to draw a thorough hydraulical, microbial and radiation profile of Slovak bentonites.

Mineralogical and Geochemical Properties of the Na- and Ca-Bentonites of Ordu (Ne Turkey)

AbstractA number of different types of bentonite deposits formed by hydrothermal alteration and diagenetic processes are to be found in the Ordu area of the Eastern Black Sea region. The Ca- and Na-bentonite deposits are related to Upper Cretaceous tholeitic to calc-alkaline volcanites, predominantly dacite and andesite, and also include rhyodacite with lesser basalt and their pyroclastic equivalents. In the present study, dacite (PR1), perlite (PR2), moderately altered rocks (MPR), and Na- and Ca-bentonites were studied to describe and compare their mineralogical and geochemical properties and their conditions of formation by means of X-ray diffraction, optical microscopy, scanning electron microscopy, and chemical analytical techniques.Ca-bentonites, except for smectite, contain opal-CT, feldspar, biotite, and rarely pyrite, while Na-bentonites contain smectite and less feldspar, opal-CT, kaolinite, and illite.Progressive alteration of the PR2 caused depletion in K2O and Na2O and enrichment in MgO and CaO in all of the Ca-bentonite samples. Na2O was depleted in all of the Na-bentonites and in most of the MPR. The medium and heavy rare earth elements (MREE and HREE) show mass gain or mass loss in the Na-bentonites. The HREE show nearly immobile behavior in the Ca-bentonites. The rare earth elements (REE) and transition elements (TRE) mostly gained mass in the Ca-bentonites in contrast to Na-bentonites. Large-ion lithophile elements (LILE) are strongly depleted in all of the bentonites. The LREE, MREE, and HREE were strongly depleted in most of the MPR samples. TiO2, Lu, Tm, and Tb show immobile behavior in all samples.PR1 exhibits a slightly positive Eu anomaly. Two MPR samples show slightly positive Eu anomalies (1.03, 1.13), and one Na-bentonite sample displays a slightly positive Eu anomaly (1.04). Most of the Nabentonites have weakly negative Eu anomalies, whereas perlite and the Ca-bentonite have a strongly negative Eu anomaly. The PR1, PR2, MPR, and Na-bentonite present a positive Ce anomaly, and the Ca-bentonite shows a moderately negative Ce anomaly. The Ca-montmorillonites are mainly hydrothermal in origin and derived from alteration of volcanoclastic material in situ and/or in the subaerial environment. The Na-montmorillonites formed by alteration and diagenesis of volcanoclastic material in the sedimentary basin.