Smectite Group Research Articles

Comprehensive characterization of bentonites from Croatia and neighboring countries

Bentonites are an important industrial resource and are also interesting from the mineralogical point of view. The main component of bentonites is a mineral from the smectite group in which chemical and structural variations, influencing bentonite properties, provide a great deal of interesting research topics. The aim of this study was to better describe bentonites from 11 known deposits from Croatia and neighbouring countries: Bednja, Bunaric, Draga, Divoselo, Sjenicak, Paripovac, Loncarski Vis and Poljanska Luka (Croatia), Zaloska Gorica (Slovenia), Sipovo (Bosnia and Herzegovina) and Vranjska Banja (Serbia). Thirteen samples were analysed using several available techniques in order to obtain the data necessary for currently accepted bentonite classification. The mineralogical composition was analysed using XRD and FTIR, and crystallo-chemical properties were investigated by thermal analysis, CEC determination with ammonium index cations, chemical analyses (ICP-AES and ICP-MS) and Mossbauer spectroscopy. The results showed that the main mineral constituent of most local bentonite deposits is a Fe-poor smectite, with a predominantly medium layer charge mostly as a result of octahedral substitutions, with calcium or sodium cations occupying the interlayer. Nevertheless, the variations between samples are prominent enough to provide a good overview of the range of crystallo-chemical properties which exist in different smectites resulting in varying bentonite properties.

Microbial Diversity Responding to Changes in Depositional Conditions during the Last Glacial and Interglacial Period: NE Ulleung Basin, East Sea (Sea of Japan)

Microbial interaction with minerals are significantly linked with depositional conditions during glacial and interglacial periods, providing a unique redox condition in the sedimentary process. Abiotic geophysical and geochemical properties, including sedimentary facies, magnetic susceptibility, grain size, clay mineralogy, and distribution of elemental compositions in the sediments, have been widely used to understand paleo-depositional environments. In this study, microbial abundance and diversity in the core sediments (6.7 m long) from the northeastern slope of Dokdo Island were adapted to characterize the conventionally defined sedimentary depositional units and conditions in light of microbial habitats. The units of interglacial (Unit 1, <11.5 ka) and late glacial (Unit 2, 11.5–14.5 ka) periods in contrast to the glacial period (Unit 3, >14.5 ka) were distinctively identified in the core, showing a sharp boundary marked by the laminated Mn-carbonate (CaM) mud between bioturbated (Unit 1 and 2) and laminated mud (Unit 3). Based on the marker beds and the occurrence of sedimentary facies, core sediments were divided into three units, Unit 1 (<11.5 ka, interglacial), Unit 2 (11.5–14.5 ka, late glacial), and Unit 3 (>14.5 ka, glacial), in descending order. The sedimentation rate (0.073 cm/year), which was three times higher than the average value for the East Sea (Sea of Japan) was measured in the late glacial period (Unit 2), indicating the settlement of suspended sediments from volcanic clay in the East Sea (Sea of Japan), including Doldo Island. The Fe and Mg-rich smectite groups in Unit 2 can be transported from volcanic sediments, such as from the volcanic island in the East Sea or the east side of Korea, while the significant appearance of the Al-rich smectite group in Unit 1 was likely transported from East China by the Tsushima Warm Current (TWC). The appearance of CaM indicates a redox condition in the sedimentary process because the formation of CaM is associated with an oxidation of Mn2+ forming Mn-oxide in the ocean, and a subsequent reduction of Mn-oxide occurred, likely due to Mn-reducing bacteria resulting in the local supersaturation of Mn2+ and the precipitation of CaM. The low sea level (−120 m) in the glacial period (Unit 3) may restrict water circulation, causing anoxic conditions compared to the late glacial period (Unit 2), inducing favorable redox conditions for the formation of CaM in the boundary of the two units. Indeed, Planctomycetaceae, including anaerobic ammonium oxidation (ANAMMOX) bacteria capable of oxidizing ammonium coupled with Mn-reduction, was identified in the CaM layer by Next Generation Sequencing (NGS). Furthermore, the appearance of aerobic bacteria, such as Alphaproteobacteria, Gammaproteobacteria, and Methylophaga, tightly coupled with the abundance of phytoplankton was significantly identified in Unit 1, suggesting open marine condition in the interglacial period. Bacterial species for each unit displayed a unique grouping in the phylogenetic tree, indicating the different paleo-depositional environments favorable for the microbial habitats during the glacial and interglacial periods.

ZSM-5 Zeolitinin Yüzey Özelliklerinin Ters Gaz Kromatografisiyle Belirlenmesi

Zeolitler, simektit grubunun mikro gözenekli üyeleridir ve endüstriyel uygulamalarda geniş kullanım alanı bulurlar. Zeolitlerin yüzey, morfolojik, mineralojik ve fizikokimyasal özellikleri farklı aletli analiz teknikleri ile incelenmiştir. Yüzey fonksiyonel grupları Fourier dönüşümlü kızılötesi (FTIR) spektrumları ile belirlenmiştir. Malzemelerin morfolojisi ve yüzey fonksiyonel grupları taramalı elektron mikroskobu (SEM) görüntüleri ve X ışını kırınım desenleri yardımıyla analiz edilmiştir. Zeolitin, Brunauer-Emmett-Teller (BET) yüzey alanı, gözenek hacmi, gözenek büyüklüğü dağılımı ve ortalama gözenek çapı da dâhil gözenek özellikleri, -196 ○C de N2 atmosferinde fiziksel adsorpsiyon ile belirlenmiştir. Zeolit yüzeyini karakterize etmek için ters gaz kromatografisi (TGK) uygulanmıştır. ZSM-5 zeoliti, Yüzey özellikleri, Morfolojik özellikler, Fizikokimyasal özellikler

Raman spectra of a graphite–nontronite association in marbles from Oltrek Island (Lake Baikal, Russia)

AbstractThe graphite in marbles from Oltrek, an uninhabited island on Lake Baikal, has been investigated by micro‐Raman spectroscopy using visible and near‐ultraviolet wavelength excitation. All graphite samples exhibit a sharp first‐order Raman band at about 1,580 cm−1 with a width from 10 to 19 cm−1, and sometimes a D1 band with very low intensity, which is occasionally absent. Using Raman spectra data it was estimated that the temperature of graphite formation in the Oltrek marbles is about 530–650°C and possibly even higher. This evaluation is in good agreement with the temperatures (about 700°C) determined by a graphite isotope geothermometer of the graphite–calcite pair. Scanning electron microscopy images have recorded a сonical graphite morphology on the surface of plate crystals of graphite. Raman spectra of samples with cones about 200–400 nm sizes showed that the graphite was associated with nontronite in the specimens studied. Natural nontronite, a clay mineral of the smectite group, has not been well characterized using Raman spectroscopy. Here, the Raman spectra of the Oltrek nontronite were compared with the spectrum of nontronite from the weathered crust of the Salair Ridge, Russia. The formation of hexagonal–pyramidal structures on the surface of graphite with the participation of clay and bio‐organic matter in marble is discussed.

Preparation of Economical and Environmentaly Friendly Modified Clay and Its Application for Copper Removal

Copper is toxic and is considered as the hazardous pollutant due to his stability in the environment. Current technologies used for its removal involve materials which can be difficult to synthesize, are expensive or are themselves potentially toxic. Natural clays are abundant worldwide, relatively cheap, possess sorption and ion exchange properties, are candidates as adsorbents. While the Cu(II) sorption capacity of raw bentonite is relatively low, modified bentonites represent a new class of sorbents for effective Cu(II) removal from wastewater. The present study investigates the influence of Algerian clay modification on the capacity of copper removal from water. This montmorillonite, which is a clay mineral of the smectite group, possesses silica tetrahedral sheets layered between alumina octahedral sheets. Several adsorbents were prepared from this bentonite by saturation with sodium, calcium and treatment with sulphuric acid to produce three adsorbents, ARS, ARC and ARH, respectively. The three materials obtained were tested for the Cu(II) adsorption from aqueous solutions. The adsorbents and metal interactions were studied under different conditions of interaction time, pH, concentration of metal ions and amount of clay. It was found that the interactions were dependent on pH, the uptake of pollutant was controlled by the amount of clay and the initial copper concentration. Langmuir and Freundlich models were fitted to experimental isotherms. The Langmuir model shows a better fit to the Cu ions adsorption isotherm for all systems. The largest adsorption capacity is observed for sodium homoionic clay. The Langmuir maximum sorption capacity of Cu(II) ions on ARH, ARC and ARS was found to be 17.241, 18.181 and 24.390 mg/g, respectively. The three adsorbents also showed a high efficiency in the Cu(II) adsorption from much diluted solutions. This work suggested that the modified clays can be promising candidates for the removal of copper ions from aqueous solutions.

Sorption of Molybdates and Tungstates on Functionalized Montmorillonites: Structural and Textural Features.

Montmorillonite—the most popular mineral of the smectite group—has been recognized as a low-cost, easily available mineral sorbent of heavy metals and other organic and inorganic compounds that pollute water. The aim of this work was to determine the sorption mechanism and to identify the reaction products formed on the surface of montmorillonite and organo-montmorillonite after sorption of molybdates (Mo(VI)) and tungstates (W(VI)). Montmorillonites are often modified to generate a negative charge on the surface. The main objective of the study was to investigate and compare the features of Na-montmorillonite (Na-M), montmorillonite modified with dodecyl trimethyl ammonium bromide (DDTMA-M), and montmorillonite modified with didodecyl dimethyl ammonium bromide (DDDDMA-M) before and after sorption experiments. The material obtained after sorption was studied by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The XRD pattern showed the presence of a new crystallic phase in the sample that was observed under an SEM as an accumulation of crystals. The FTIR spectra showed bands related to Mo–O and W–O vibration (840 and 940 cm−1, respectively). The obtained results suggest that molybdenum(VI) and tungsten(VI) ions sorb onto the organo-montmorillonite in the form of alkylammonium molybdates and tungstates.

New insights of Auger spectroscopy for the identification of Fe-Si compounds in iron/glass corrosion systems at nanoscale

In the context of high-level radioactive wastes (HLW) storage, long term alteration of glass and corrosion of metallic containers leads to the formation of sub-micrometric phyllosilicate phases in the iron Corrosion Product Layer (CPL). The nature of these phases, their properties (porosity, electronic, passivation…) and their spatial distribution must be identified to determine their exact role in the iron corrosion process and to efficiently predict the long-term alteration of nuclear wastes package. In this work, the capabilities of localized Auger spectroscopy, combining surface chemical determination and high spatial resolution, to characterize these phyllosilicate phases is presented. In the present context, the main challenge to overcome was the insulating character of the different compounds and samples, presenting a real disadvantage for Auger implementation. A specific experimental protocol had to be developed to enable acquiring exploitable spectra at sufficiently high resolution to obtain identifiable fingerprints. The main Si-KLL Auger transition of different types of phyllosilicates representative of those encountered in the CPL of the glass-iron systems was acquired to determine if different chemical signatures and chemical shifts could be observed in function of the structure of reference phyllosilicates phases. Indeed, the Si-KLL kinetic energy position value of the phyllosilicate increases with the structure according the following order: smectite group < chlorite group < serpentine group and different line shapes are observed. The significant contribution of the present study relies on the achievement of analyzing such insulating materials by Auger at nanometric scale using a new generation Auger nano-probe (spot size around 12 nm) without drastic preparation requirements, enabling to constitute a Si-KLL Auger data base of phyllosilicates. Thanks to this preliminary analytical approach, the Si-KLL fingerprint measured in the CPL of the glass/iron system altered in an anoxic reactor at 90 °C in synthetic Callovo-Oxfordian (COx) clay-based groundwater solution could be identified as serpentine phyllosilicate. Transmission electron microscopy (TEM) analysis was also used to characterize phyllosilicate and reinforce the AES approach identification, confirming the presence of serpentines.

Stevensite-Rich Moroccan Clay Intercalated by Polypyrrole: Towards the Enhancement of Electrical Conductivity.

Regularly arranged chains strongly affect the electrical conductivity of conductive polymers (e.g., polypyrrole). One of the easiest ways to achieve this arrangement is the insertion of the polymer into the interlayer space of solid inorganic layered matrix, i.e., the intercalation process. Among various kinds of layered materials, the clay minerals, especially the smectite group, deserves particular attention. Negative charge of smectite layers helps the intercalation process resulting in higher conductivity of the polymer in clay/polymer intercalates. Characterization of stevensite-rich Moroccan clay and intercalation of electrically conductive polypyrrole into stevensite-rich Moroccan clay in order to obtain material with higher conductivity in comparison with pure polypyrrole were two main purposes of this work. Two forms of stevensite/polypyrrole nanocomposites were studied: powder and pressed tablets. X-ray fluorescence spectroscopy, X-ray diffraction analysis, atomic force microscopy, thermogravimetry, infrared spectroscopy, Raman microspectroscopy, and scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy were used to study the composition and structure of the nanocomposites. Measurement of electrical conductivity of polypyrrole in stevensite/polypyrrole nanocomposites revealed enhanced conductivity for all samples and also anisotropy in the conductivity of the samples pressed in the tablets.

Mineral Precipitation from CO2-Saturated Water in Basalts and its Potential for Self-Sealing of Fractures and Joints

Continental flood basalts are considered as potential CO2 storage reservoirs; however, many knowledge gaps have not been addressed. This study determines whether mineral precipitation will seal joints and fractures during the vertical migration of CO2-enriched water and thereby contribute to CO2 containment. The interaction of CO2-saturated water with basalt wafers was studied in a batch reactor at a pressure of 80 bars and 60°C for a period of 44 days. Si-Al-rich minerals such as smectites and zeolites were observed in suspension at the end of the incubation. In addition, mineral precipitation on at the surface of the basalt wafers was identified as magnesite, kaolinite and Mg- and Fe-oxides. Na-rich Si-Al minerals were identified as Na-nontronite, which belongs to the smectite group. All cation concentrations declined between incubation day 6 and 44. Mineral saturation indices have been computed for the experimental solution as a function of time to observe supersaturated and undersaturated mineral phases. Smectites, zeolites, Fe-oxides, and kaolinite are observed to be supersaturated in the experimental fluid till the end of the reaction time period of 44 days which matches closely with the experimental secondary mineral phases. These secondary minerals could be potential sealants and mitigate CO2 leakage issue.

Lithofacies analysis and economic mineral potential of a braided fluvial succession of NW Himalayan foreland basin Pakistan

This study has described detailed lithofacies analysis, clay mineralogy, and depositional setting, and highlighted economic mineral potential of late Miocene to Early Pliocene mid Siwalik Dhok Pathan Formation. The Siwalik fluvial sedimentary succession is 5300 m thick in the NW Himalayan foreland fold-and-thrust belt known as Surghar-Shingar Range (SSR). The middle Siwalik (Dhok Pathan Formation) typically represents cyclic alternation of massive sandstones, siltstones, mudstones, and claystones in repeated fining upward rhythm with varied thicknesses from 807 to 1540 m. Detailed sedimentological investigations resulted in the identification of seven distinct lithofacies (Gt, St, Sh, Ss, Sl, Fm, and Fl) which had been deposited by sand-dominated bed load braided fluvial system. The facies Sh is hosting detrital uraninite identified through a scanning electron microscope (SEM). X-Ray diffraction analyses revealed that kaolinite, smectite (montmorillonite and saponite), illite, vermiculite, and chlorite (clinochlore and chamosite) are the main clay mineral suits present in the formation. The morphology of clay mineral suits is indicative of weathering products or contribution from the source areas. The absence of glass shards and mineral analcimolite evidenced that these smectite group clay minerals were not derived from the devitrification of volcanic ashes. The sedimentological analysis, mineralogical composition, and paleo-flow directions revealed that these sediments had been deposited by NS fluvial system presently known as Indus River system in this area. The rare earth element concentrations of sandstone and heavy minerals laminations (black sand) show enrichment of uranium (662 ppm), thorium (1374 ppm), La (975 ppm), Ce (2831 ppm), Pr (193 ppm), Nd (746 ppm), Gd (98 ppm), and Dy (50.8 ppm), which specify good indicative economic mineral potential of the formation.

Geochemistry and Mineralogy of the Upper Cretaceous-Paleocene Marine Series, Iullemmeden Basin, Niger Republic

Major and trace elements, mineralogy as well as the total organic content of the Upper Cretaceous-Paleocene Marine Series of the Iullemmeden basin in Niger were determined in order to assess their composition, the chemistry of the paleoenvironment and the nature of the parent crystalline rocks that they evolved from. The major and trace elements were analyzed using a Bruker Tracer IV energy-dispersive hand held X-ray fluorescence spectrometer, the mineralogical analyses were done using a Bruker AXS D8 Discover, while the total organic carbon was calculated by subtraction of inorganic carbon from the total carbon, determined using a CM5014 coulometer (UIC, Joliet, IL, USA) and a LECO SC-144DR instrument. Geochemical indices calculated from major oxides such as CIA, PIA, ICV and CIW have been computed and the results show that the Marine Series are made essentially of clay minerals of the smectite group (montmorillonite), quartz and other accessory minerals like rutile and calcite. Computed ratios of some trace elements such as V/(V + Ni) and V/(V + Cr) showed that the paleoenvironment was dysoxic-oxic and the low values (2O3/TiO2 ratios, the sediments were derived from intermediate to acidic igneous rocks surrounding the basin.

Cell viability and bacterial reduction activity of Ag-modified bentonite

Abstract The interest on the potential biomedical applications of clay materials are recently growing. Among the clay minerals, it was found that the smectite group clays are the most suitable for adsorption processes. This group includes bentonite in which the structure is composed of octahedral and tetrahedral layers of silica. In this study, bentonite clays from SAILE Industries, Inc. in Mangatarem, Pangasinan, Philippines were characterized and fabricated as Ag-bentonite composites to determine the potential of the mineral for biomedical applications. Bentonite clay powder was mixed with silver nitrate solution via ion-exchange process. The synthesized powders were filtered using centrifugation and washed with deionized water to remove any excess silver ions. Drying followed at 60°C and stored in a dark container prior to characterization. XRD and XRF was used to evaluate the phase composition and chemical analysis of the Ag-bentonite composite, respectively. The biological tests were also done to investigate the antibacterial and cell viability of the sample.XRD result showed that the sample is composed of the montmorrilonite, hectorite and mordenite phases. Chemical analysis revealed the presence of Ag in the bentonite structure with a content of about 14.24±0.13%. Antibacterial activity of the sample was evaluated using plate reduction method where about 99% reduction of S. Aureus was observed after 24 h. Moreover, approximately 89±4.37% live cells was detected after the 24-h incubation of the sample using lymphocyte culture. With these results, the synthesized AgB samples may find suitable future biomedical use due to its stable structure, antibacterial and biocompatibility properties

Fines quality assessment in all-in aggregates for pavement layers related to different standard procedures

During the construction of the unbound pavement layers of Corridors X and XI in Serbia, a problem was detected regarding the evaluation of cleanliness of the available materials. The European standard for the sand equivalent from 1999 to 2015 had significant changes related to the test procedure. A mass correction has been taken into account. It consists of replacing a part of the fines with rinsed material (0.063/2 mm) when the percentage of fines exceeds 10% in a tested fraction. Thus, the test sample usually yields high values of the sand equivalent, which often exceeds the limits of 50% and 60%. From the standpoint of the technical specifications, aggregates are considered clean, while using other methods like methylene blue or a plasticity index, the presence of clay particles above the limits can be confirmed. This paper presents the results of research on 63 laboratory-prepared test samples of limestone aggregate with small quantities of the smectite group of clay minerals, where the fines content in the unbound aggregate, 0/31.5 mm, gradually increased up to 20%. It was found that the sand equivalent values are continuously decreasing from 84 to 14% in the fraction 0/2 mm and from 87 to 18% in the 0/4 mm fraction, with increasing of the methylene blue value of the all-in aggregate (MBA) from 0.4 to 4.5 g/kg. Correlations of different methods and fractions, as well as with the content of fines were found. There are no correlations with SE10 because of grouping the test data around one point.

Microwave-Assisted Acid Activation of Clays Composed of 2:1 Clay Minerals: A Comparative Study

The effect of the microwave-assisted acid treatment (MAT) on the structure and texture of dioctahedral (montmorillonite) and trioctahedral (saponite) smectites, kerolitic clays and sepiolites were studied by scanning electron microscopy, nitrogen adsorption, X-ray fluorescence, X-ray diffraction and Fourier transform infrared spectroscopy. This study shows that in the smectite group of minerals the effectiveness of MAT is notably influenced by the chemical composition of the octahedral sheet, whereas in kerolitic clays it is influenced by the proportion of the expandable phase in the mixed layer sequence. On the other hand, the reactivity of sepiolites depends on the width of the natural fibres. With these treatments, extremely high specific surface area (SSA) increments are achieved in just 16 min. The SSA increments reach values up to 231 m2/g (%ΔSBET = 80) in sepiolites, 198 m2/g (%ΔSBET = 155) in Mg-smectites, and 161 m2/g (%ΔSBET = 61) in kerolitic clays.

Routine investigation of structural parameters of dioctahedral smectites by the Rietveld method

Abstract X-ray powder diffraction (XRD) in combination with the Rietveld method is a common technique for crystal structure analysis. However, almost all minerals of the smectite group show turbostratic disorder preventing the direct application of Rietveld refinement. Ufer et al. (2004) proposed to overcome this limitation by using a single layer model with the BGMN program. This model is now routinely used for quantitative phase analysis of smectite-containing samples. However, the refinement of some important structural features, such as the layer charge density (LCD) and the octahedral iron content has not been achieved successfully yet. Typically, these structural features can be obtained only by analytical methods which require purified smectite samples. The project was firstly aimed to prove the validity of the refinement of selected structural parameters by using a set of purified and well-characterized samples and then applied this method to raw bentonites with natural impurities. The Rietveld refinements were carried out on the X-ray powder diffraction patterns of the Cu-triethylenetetramine (Cutrien) exchanged dioctahedral smectites to avoid the problems of unknown cation species and complex hydration behavior in the interlayer. The refinements of the occupancy of octahedral iron and the LCD led to reasonable results for iron-poor purified samples. The application of the structure model to Cutrien -exchanged smectite-rich samples with natural impurities, e.g. bentonites without previous purification, showed that some important structural details of turbostratically disordered dioctahedral smectites can be determined by the Rietveld method from XRD patterns of the Cutrien -exchanged samples. The technique may be applied in routine structural characterization of raw smectites in bulk rock samples without a prior chemical analysis of purified smectite fractions.

Beneficiation of Fine Coal Tailings From Coal Preparation Plant by Enhanced Gravity Methods

In the past, it was more economical to dispose fine coal without utilization. Nowadays, beneficiation of fine coal is a necessity due to increasing costs of mining, tailings disposal and storage problems. This research contains experimental studies devoted to beneficiation of &amp;lt;0.1 mm coal preparation plant tailings of Garp Lignite Enterprises (Tunçbilek- Kütahya/Turkey). It was found from the characterization studies that the coal tailings include clay minerals (kaolinite, mica/illite, and smectite group), quartz, siderite, pyrite and dolomite which are of higher density than lignite coal. Concentration processes are proposed as preliminary and final processing. In the preliminary two-stage processing tests, hydrocyclone is used to separate clay minerals associated with coal. For this purpose, structural and operating parameters of hydrocyclone (hydrocyclone diameter, vortex diameter, apex diameter, feed inlet pressure, pulp solids ratio) and of Falcon concentrator (gravity force, feed rate, pulp solid ratio and wash water pressure) are optimized, and their influences on separation efficiency were discussed. Under optimum opened flowsheet, the fine clean coal concentrate assay was 35.66% ash and 1.63% total sulfur at a recovery of 34.60%.

Use of asid-activated saponites as natural sorbents

The composition, structure, and adsorption properties of natural saponites from the smectite deposit of the Khmelnytsky region have been studied. It is shown that saponites are environmentally friendly clays containing biologically active microelements as isomorphic impurities. It was established that acid activation increases the content of acid surface centers and the adsorption activity of saponites. Based on the study conducted by the authors, it is proposed to use natural saponites not only as adsorbents and fodder additives, but also in medicine. As a result of our studies it was established that the use of natural raw materials - saponites of the Khmelnitsky layer - allows their ecological purity and rich mineral composition. After acid activation, such saponites have a sufficiently high content of surface acid sites, which causes their cationic activity. In general, this gives universality to saponites from the smectite group and opens up broad prospects for their use in medicine - as a substance for the manufacture of efferent drugs; veterinary medicine as a mineral supplement for animal feed; in agriculture as a fertility stone; as well as for the protection of the environment - the development of technologies for cleaning and disinfecting water of various degrees of pollution.

Effect of clayey groundwater on the dissolution rate of SON68 simulated nuclear waste glass at 70 °C

To predict the long-term behavior of high-level radioactive waste glass, it is necessary to study aqueous dissolution of the glass matrix under geological repository conditions. The present article focuses on SON68 (an inactive surrogate of the R7T7 glass) glass alteration in synthetic clayey groundwater at 70 °C. Experiments in deionized water as reference were also performed in the same conditions. Results are in agreement with those of previous studies showing that magnesium present in the solution is responsible for higher glass alteration. This effect is transient and pH-dependent: Once all the magnesium is consumed, the glass alteration rate diminishes. Precipitation of magnesium silicate of the smectite group seems to be the main factor for the increased glass alteration. A pH threshold of 7.5–7.8 was found, above which precipitation of these magnesium silicates at 70 °C is possible. TEM observations reveal that magnesium silicates grow at the expense of the passivating gel, which partly dissolves, forming large pores which increase mass transfer between the reacting glass surface and the bulk solution.

MUNICIPAL WASTEWATER TREATMENT WITH BENTONITE FROM MILOS ISLAND, GREECE

Bentonite clay minerals belonging to the smectite group have a wide range of chemical and industrial uses. The structure and chemical composition, exchangeable ion type and small crystal size of smectite are responsible for several properties, including a large chemically active surface area and a high cation exchange capacity. A wastewater treatment using bentonite from Milos island, Greece, was investigated. Raw wastewater sample (influent) from the wastewater treatment plant (WTP) of the city of Kilkis, Northern Greece was treated using bentonite in conjunction with chemical coagulants (polyaluminium chloride-PAC and cationic polyelectrolyte), in batch type experiments. Theremoval of suspended solids (SS), chemical oxygen demand (COD), nitrate ion, ammonium ion, phosphate ion, and toxic metals were evaluated. The treatment gave overflowed clear water improved concerning the quality parameters. The bentonite adding prior to flocculation resulted in effective removal of heavy metals such as chromium and copper. Additionally, the bentonite removed nitrogen compounds with relatively high efficiency, while the clay presence highly improved the COD removal. The quality parameters after treatment were improved fulfilling the requirements for disposition as downstream, irrigation, swimming and fish waters.

Structural, geochemical, and mineralogical investigation of active hydrothermal fluid discharges at Str\xfdtan hydrothermal chimney, Akureyri Bay, Eyjafj\xf6r\xf0ur region, Iceland

A submarine hydrothermal fluid discharge structure in Akureyri Bay, Eyjafjörður region, Iceland, was investigated by means of structural, geochemical, and mineralogical methods. Thermal and chemical gradients between the hydrothermal fluid and the subarctic seawater lead to an ongoing mineral precipitation. This process builds up hydrothermal chimneys of dozens of meters in height and they are still growing. The structural analysis reveals an internal stratification of the mineral precipitates at various scales from sub-micrometers to several decimeters. This stratification indicates random changes in the depositional system during the formation of the hydrothermal cones. Some mineral layers are characterized by a dominance of Si, Mg, and O. In contrast, others are dominated by Ca and O. However, the results of XRD analysis proved that the material consists mainly of a trioctahedral phyllosilicate of the smectite group, presumably saponite or stevensite. Additionally, aragonite and hisingerite could be present. The material is built up of numerous parallel tubes, which act as conductors in the hydrothermal chimneys. Consequently, a large amount of available pore space with pore volumes of up to 6 mm3 was detected in the sample by the porosity analysis.