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The sorption properties of various clay minerals and materials based on them in relation to Cs(I), Sr(II), U(VI), Eu(III), and Pu(IV,V,VI) are compared. To determine the mineral composition, all the samples are studied by X-ray diffraction and X-ray fluorescence, the values of the specific surface are determined, and sorption experiments are carried out. It is shown that the high concentration of swelling clay minerals (montmorillonite, mixed-layer clay minerals) in the barrier material will contribute to its high sorption capacity in relation to the majority of the studied radionuclides.

This article is devoted to the comparison of various methods for the quantitative determination of montmorillonite content in bentonite clays based on the adsorption of organic molecules and cations. The studies were conducted on samples of natural bentonite clays of the main Russian industrial deposits and the CIS: 10th Khutor (Republic of Khakassia), Zyryanskoe (Kurgan region), Dash-Salakhlinskoe (Republic of Azerbaijan), Dinozavrovoe (Republic of Kazakhstan). All samples selected for the study are characterized by a high content of montmorillonite (more than 70 %). As reference values ​​for the contents of montmorillonite, we used the data of X-ray diffraction analysis according to the Rietveld method. As the tested methods, the most common approaches were used both in the research and industrial sectors of Russia, based on the adsorption of a mixture of rhodamine 6zh and chrysoidine dyes (GOST 28177-89), adsorption of methylene blue dye and adsorption of copper (II) complex with triethylenetetramine (Cu-trien), as well as thermal characteristics after saturation with organic compounds. The best convergence of the montmorillonite content values ​​was shown by modified techniques based on the adsorption of methylene blue dye and the adsorption of the Cu-trien complex. Other methods are characterized by a large measurement error. A common problem with these methods is overs equivalent adsorption on highly charged alkaline bentonites and reduced adsorption on alkaline earth bentonites, as well as the presence of impurity minerals and amorphous phases capable of sorption in the composition of bentonite. The research results can be used to compare the results of the content of montmorillonite, cited by various authors in scientific publications and used in production.

This investigation made it possible to compare the sorption capacity of mineral and organic sorbents in respect to U(VI). In order to establish the patterns of sorption, natural sorbents with a high content of rock-forming mineral were used: glauconite, diatomite, zeolite, peat, brown and hard coals, shungite. Each sample was characterized using X-ray diffraction, X-ray fluorescence method, scanning electron microscope, XPS spectra, potentiometric acid–base titration and surface area measurement. The partitioning of U(VI) was determined by sequential extraction technique. It was shown that the highest sorption ability and strongest interaction towards U(VI) is common to peat and brown coal.

Mineral composition, physicochemical properties and sorption characteristics of clay-salt slimes (CSS), wastes formed in processing of the sylvinite ore at JSC “Belaruskali” (Soligorsk, Belarus) and aluminosilicate and illite sorbents produced on their basis were studied. It was shown that dressing of CSS samples results in that their chemical and mineralogical compositions change. It was found that the washing of CSS with water, followed by treatment with hydrochloric acid and Trilon B, leads to a 1.2–1.3 times increase in the content of the main component of CSS, illite, due to the dissolution of carbonates (dolomite and calcite) and gypsum. It was found that presence of illite plays a key role in the sorption activity of the sorbents toward the radionuclides 137Cs and 90Sr. With enriched samples of illite sorbents (IS-3o and IS-3m),the distribution coefficients of 137Cs become twice larger, and those of 90Sr, 20 times larger in comparison with the undressed samples of aluminosilicate sorbents (AS-3o and AS-3m). It is shown that the production of aluminosilicate and illite sorbents from CSS and the use of these sorbents for purification of liquid radioactive wastes to remove the radionuclides 137Cs and 90Sr and for creating barriers providing the safe storage and burial of low- and medium-activity of radioactive wastes are promising.

—The sorption characteristics of the Kara sea bottom sediments were investigated. The sediments were collected during scientific expedition of the R/V Akademik Mstislav Keldysh (Cruise AMK-66). The mineral and fraction composition of the sediments was determined. It has been found that 137Cs is sorbed mainly by an ion exchange mechanism because of the clay minerals presence in sediments. At the same time, 243Am and 90Sr sorbed from seawater by the surface complexation mechanism. It has been established that the sorption kinetics of 243Am, 137Cs, and 90Sr is about 20 hours, 2 hours, and less than an hour, respectively. The Cs and Am sorption isotherms in experiments with sea and deionized water are described by the Henry equation. The Sr behavior in the deionized and sea water is described by the Langmuir and Freindlikh equations, respectively.

The sorption behavior of Np(V) and Cs(I) on natural and acid-treated bentonite-like clay of Ostro-zhanskoe deposit (Belarus) was studied in a wide range of radionuclide concentrations and pH values of the suspension. The sorption equilibrium with both radionuclides is attained within the first minutes of the interac¬tion. The sorption behavior on the untreated and treated clay is similar. Based on the experimental data, ther-modynamic modeling of the Cs(I) and Np(V) sorption onto the clays was performed.

The sorption of Eu(III) onto montmorillonite samples from different deposits such as those of Kutch (India), 10th Khutor deposit (Russia), and Cortijo de Archidona (Spain) was studied over a wide range of experimental conditions by varying the total Eu concentration, pH, and ionic strength. Various bentonite samples showed quantitative sorption at all pH values at low ionic strengths of the solution because of ion exchange interactions. At a higher ionic strength (1 M NaClO4), the sorption is pH-dependent because of the interaction with edge sorption sites and it differed from sample to sample. The difference in the mechanism of interaction at different ionic strengths was confirmed by time-resolved laser-induced fluorescence. Thermodynamic modeling was performed with all experimental data for montmorillonite samples from different sources to create a generalized model for describing their interaction with Eu(III).

Bentonites are often used as components of engineered barrier systems (EBS) for the radioactive waste disposal and isolation of hazardous nuclear facilities. In this paper, we consider possible transformations of the composition, structure and properties of bentonites when they are used as EBS components during the decommissioning of open pools with liquid radioactive waste (LRW). Operating conditions were modeled by the treatment with nitric acid at different durations (from 1 to 6 h), concentrations (from 1 to 8 M) and temperatures (20and 90°C). Nitric acid was chosen because it is used in the preparation procedure of LRW for isolation. To assess the intensity of transformations, bentonites with a high content of Al- and Fe-rich montmorillonites were selected. The work revealed effects of interlayer modification, leaching of octahedral cations, changes of the grain size distribution, specific surface area and weakening of surface basicity. It was also shown that temperature has a stronger effect on the structural transformation of montmorillonite than acid concentration and treatment duration. Formation of Al hydroxy-interlayered (HI) layers was observed due to the treatment with the nitric acid of lower concentration (1 M). The effect of a higher concentration at the same treatment duration and temperature leads to a more intensive leaching of Al from the octahedral sheets and protonation of the interlayer, which prevents the formation of Al hydroxy-interlayered (HI) layers. CO2 desorption after the nitric acid treatment decreases significantly, maintaining a relatively high value only when the conditions allow the interlayer to be protonated. Modification of structural and adsorption characteristics due to the acid treatment can be used to simulate modification of the engineered barriers' properties for a long-term operation in the disposal of radioactive and toxic wastes.

Phase composition, particle morphology, and granulometric composition of commercial samples of MgO powders of various chemical purities (classification from technical grade to chemical grade) prepared by heat treatment at 1300°C for 3 h were studied for the subsequent synthesis of a compound based on magnesium potassium phosphate matrix MgKPO4·6H2O, promising for solidifying liquid radioactive waste. It has been established that to obtain a homogeneous mineral-like compound with compressive strength of about 15 MPa, which meets the regulatory requirements for solidified forms of liquid radioactive waste, it is necessary to use magnesium oxide powder with a particle size of not more than 50 μm, which have a high degree of crystallinity (the average crystallite size is not less than 40 nm). It was noted that the impurities of metal compounds, primarily silicon, calcium, and iron in the MgO powder, do not affect the synthesis conditions and the mechanical strength of the compound.

Clays have been adopted in most nuclear waste producing countries as a key constituent in engineered barrier systems for final disposal facilities at all levels of radioactive wastes (LILW-SL, LILW-LL, and HLW). The following study presents a thorough characterization upon five Brazilian clay-rich deposits, mostly smectite bearing clays, aiming to evaluate their expected performance as barrier under the conditions associated to a Low and Intermediate Level Waste Repository; being the former a matter of national strategic interest. Samples coming from the Brazilian states of Paraná, Bahia, Paraíba, and Maranhão were treated and analyzed by means of X-Ray diffraction as main technique, and complemented by FTIR, LALLS, XRF, and SEM-EDS, in order to establish the mineralogical composition, particle size distribution, and chemical composition. Moreover, several standard clay treatments over the

Nizhne-Koshelevskoe and Verkhne-Pauzhetskoe thermal fields are located in the south of Kamchatka, the first - within the Koshelevsky volcanic massif, the second - on the territory of the Pauzhetsky geothermal field. The first horizon from the surface in these fields is formed by clayey soils, that have been formed as a result of hydrothermal alteration of volcanic rocks. And in the natural conditions clayey soils are at temperatures reaching 100 °C.Samples of undisturbed clay soils were taken within the thermal fields. The samples are characterized by a density of 1.29 - 1.42 g/cm3, rather high values of the weight moisture (90-110%), and temperatures of 50 - 70 °C.The samples are dominated by clay minerals: kaolinite and mixed-layer - kaolinite-smectite, their content is about 75%. The other 25% are microcline, cristobalite, anatase, gypsum, pyrite, marcasite, quartz and alunite.For samples of undisturbed clay soils, direct shear tests were carried out at a temperature of 20 °C and at a temperatures of the samples close to their natural temperatures (50–70 °C). Thus, the values of cohesion and the angle of internal friction of the samples were determined.The obtained results can be interfered as follows: as a result of an increase in the temperature of clayey soils, the thickness of electric double layer on the surface of clay particles decreases. On the one hand, it leads to a decrease of cohesion value between the clay particles and the beginning of shear deformations at lower vertical loads. On the other hand, a smaller thickness of electric double layer brings particles closer to each other, which is the reason for an increasing angle of internal friction and shear resistance at higher vertical loads.

10th Khutor deposit is located in the Republic of Khakassia and confined to the coal-bearing formation of Carboniferous age within the development of continental tuff-sandy-argillaceous sediments. In terms of mineral composition, bentonites are mainly composed of Al-rich montmorillonite. The content of montmorillonite reaches a maximum of 70-75%, with an average content of 55 to 70%. It is one of the main sources of bentonite for the metallurgical and foundry industries in Russia. One of the distinctive features of bentonites from the 10th Khutor deposit is that despite the age of the deposit, about 350 million years, and the presence of an initial phase of metamorphism, as evidenced by the formation of hard coal, these bentonites retained the ability to swell and have high thermal stability. The formation of bentonites is associated with the decomposition of volcanic ash of rhyodacite and dacite composition in zones of shallow seawater - bays and lagoons. The properties of bentonite were influenced by the initial stage of metamorphism. The main purpose of this work was to establish the conditions for the formation of this deposit, as well as to study the features of the mineral composition and physicochemical properties of these raw materials. In addition to fundamental issues, the aim of the work was applied research on the properties and quality of bentonites.

The sorption of Cs + onto raw Kutch clay (India) over a wide range of concentrations and pH levels was studied and compared with its sorption onto the well-studied FEBEX clay (Spain). The principal clay mineral in both samples is montmorillonite. Non-linear sorption isotherms were measured for both clays. The shapes of the isotherms prompted the use of a two-site exchange thermodynamic model to describe the experimental data. However, differences in the highly selective sorption sites (Type 1) were observed for the two studied clays. It was found that the presence of different cations (H + , Ca 2+ , Mg 2+ , etc.) in solution affected the sorption of Cs + . A model accounting for the competition process was developed for predicting the behavior of the raw clay in complex solutions.

Analysis of the evolution of bauxite-bearing weathering crust in the geological history of Asia, as well as detailed mineralogical–geochemical and hydrogeochemical studies, has made it possible to consider supergene infiltration metasomatism as a single mechanism for the formation of the eluvial zonal profile, using the weathering crust of southern Vietnam weathering crust as an example. It is established that all weathering crust zones develop simultaneously throughout the existing fracturing as rocks interact with the solutions percolating through them. All supergene minerals are formed directly from original parent rock components rather than by staged development at each other’s expense. The resulting paragenetic assemblages of newly formed minerals result in zoning.

In this work, we study different clay samples to examine the effect of structural features of clay minerals (2:1 and 1:1 structures), interlayer cations (Na/Ca/Li forms of montmorillonite), surface area and presence of accessory minerals (iron oxides, calcite, quartz) on Np(V) sorption at trace concentrations. Various techniques, e.g., XRD, XRF, DTG, FTIR, BET absorption and Mossbauer spectroscopy, were used to characterize these clays. The presence of iron oxide as an accessory mineral has a strong effect on Np(V) sorption. Sorption of Np(V) onto different clay minerals with different surface areas, interlayer cations and structures is very similar at a pH range of 4.5–11.5.

The samples of the magnesium potassium phosphate (MPP) matrix have been synthesized during solidification of the simulator of acid intermediate level waste. The main phase of the obtained samples corresponds to MgK1−x(NH4)xPO4 × 6H2O. The behavior of the matrix components during leaching with bidistilled water according to the semi-dynamic test GOST R 52126-2003 has been studied. The high hydrolytic stability of the MPP matrix to leaching of 137Cs, 90Sr, 239Pu and 241Am exceeding the stability of the cement matrix has been shown. It has been found that the components leaching process is controlled by various mechanisms due to the formation of the salts with different solubility.

Low-temperature mineral-like magnesium potassium phosphate (MPP) compounds were synthesized in the course of immobilization of nitric acid solutions containing cesium, strontium, sodium, ammonium, lanthanum, and iron as simulated radioactive waste (RW). The phase composition and structure of the compounds and the distribution of the RW components were studied. The mechanical strength (15 ± 3 MPa), heat resistance (up to 450°С), and radiation resistance (absorbed dose 1 MGy) of the compounds were evaluated in accordance with the existing regulations. The MPP compound exhibits high hydrolytic durability: The differential leach rate of 239Pu and 152Eu on the 28th day, measured in accordance with GOST (State Standard) R 52 126–2003, is 2.1 × 10–6 and 1.4 × 10–4 g cm–2 day–1, respectively. Introduction of wollastonite into the compound decreases the radionuclide leach rate by a factor of up to 5. The MPP compound shows promise for industrial solidification of liquid RW, including high-level highly saline multicomponent actinidecontaining waste.

Batch sorption experiments on thoroughly characterized bentonites and thermodynamic modeling studies were conducted to reveal the role of iron-containing accessory phases on the interfacial behavior of Np(V). Bentonite clays from different industrial deposits with varying total iron contents were selected for the studies. The samples were characterized by XRD, Mossbauer spectroscopy, XRF, HRTEM, SEM-EDX and other techniques, and wherever possible, the accessory iron phases were identified and quantified. Thermodynamic modeling using available surface complexation data revealed the dominant role of the goethite accessory phase, which was present as nanoparticles, in Np(V) sorption at trace level concentrations (10 −14 M). This fact is independently supported by the combination of SEM-EDX and α-track radiography. These studies illustrate the important role that accessory minerals can play in radionuclides sorption data. This is important to the understanding and modeling of the molecular-level speciation of radionuclides.

We have analyzed the specific features of the mineralogical composition of bottom sediments of Blagopoluchiya, Tsivol’ki, and Abrosimov bays and soils on Cape Zhelaniya and the coasts of Abrosimov and Stepovoi bays. The data were obtained during two scientific expeditions of the R/V Professor Shtokman in 2014 (cruise 128) and R/V Akademik Mstislav Keldysh in 2015 (cruise 63). These investigations revealed patterns in the transportation of terrigenous material in the coastal zone of the bays: a decrease in the share of nonclay minerals and an increase in that of clay minerals with distance from shore. The increase in kaolinite and smectite content in soil horizons is related to biochemical weathering, while illite is mainly formed as a result of physical weathering.

This paper presents the results of the first experimental thermochemical investigation of two natural trioctahedral chlorites (clinochlores). The study was performed with the help of a high-temperature heat-flux Tian-Calvet microcalorimeter. The samples were characterized by X-ray spectroscopy analysis, X-ray powder diffraction, thermal analysis, and FTIR spectroscopy. The enthalpies of formation of clinochlores were found using the melt solution calorimetry method to be: −8806 ± 16 kJ/mol for composition ( Mg 4 . 9 Fe 0 . 3 2 + Al 0 . 8 ) [ Si 3 . 2 Al 0 . 8 O 10 ] ( OH ) 8 and −8748 ± 24 kJ/mol for composition ( Mg 4 . 2 Fe 0 . 6 2 + Al 1 . 2 ) [ Si 2 . 8 Al 1 . 2 O 10 ] ( OH ) 8 The experimental data for natural samples allowed calculating the enthalpies of formation for end-members and intermediate members of the clinochlore (Mg 5 Al)[Si 3 AlO 10 ](OH) 8 and chamosite (Fe 5 Al)[Si 3 AlO 10 ](OH) 8 series. An important feature of the clinochlore structure is the presence of two distinct hydroxyl-containing octahedral layers: the interlayer octahedral sheet and octahedral 2:1 layer; the enthalpies of water removal from these positions in clinochlore structure were determined as: 53 ± 20 kJ/(mol·H 2 O) and 131 ± 10 kJ/(mol·H 2 O), respectively. These obtained first thermodynamic characteristics of Mg-Fe clinochlores can be used for quantitative thermodynamic modeling of geological and industrial processes including clinochlores of different composition.

Natural kaolin and the metakaolin obtained by calcination of kaolin at 650 °C were chemically activated using 0.25–3.0 mol/dm3 HCl solutions. Structural and textural properties of samples were characterized by X-ray diffraction, elemental analysis and N2-adsorption/desorption analyses. The amount of Bronsted acid sites (BAS) was determined by infrared spectroscopy using pyridine as probe molecule. The amount of BAS for kaolin rose with increasing HCl concentration up to 1.0 M, and decreased for higher concentrations, that is related with the leaching of Al from the solid. Effect of HCl concentration on amount of BAS was negligible for metakaolin. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2H-chromen-4-ol, carried out in toluene at 50 °C. The reaction rate and the selectivity toward octahydro-2H-chromen-4-ol depended on the Bronsted acidity, structural and textural properties of the catalysts. The reaction rate in the presence of kaolin modified by HCl correlated with the amount of BAS. HCl-kaolin samples were more active compared with HCl-metakaolin, while selectivity reaction toward octahydro-2H-chromen-4-ol was larger in the presence of HCl-metakaolin.

This work considers terrestrial coastal landscapes of Abrosimov and Stepovoi gulfs and Yuzhnii (Southern) Island in the Novaya Zemlya Archipelago in the Kara Sea. These areas are dominated by horizons of slightly acidic leptosols and lithic leptosols of 10 cm thick (Stepovoi Gulf) and those of weak skeleton acidic lithic leptosols of 10–15 cm thick (Abrosimov Gulf) covered by moss–shrub assemblages. Kaolinite is formed in a rhizosphere fine earth layer; illite is formed along the leptosol sequence. The studied coastal landscapes are characterized by low accumulation potential of chemical elements, including radionuclides, at higher contents of them. Elements such as Fe and Ti are dispersed in sols, whereas P, S, Cl, Cu, Pb, and Zn are accumulated in soils in minor amounts. Plants accumulate S, P, Cl, Sr, Zn, and 137Cs in minor amounts as well. Elements such as Ti, Mn, Fe, Cr, V, Co, Ni, Cu, Rb, Zr, Ba, Th, Y, Nb, Pb, and As are attributed to the group of weak biological adsorption. The specific 137Cs activity (Bq kg–1) amounts to 10–150 in plants, 10–300 in moor leptosol horizons, and 1–40 in mull horizons.

Subaerial endolithic systems of the current extreme environments on Earth provide exclusive insight into emergence and development of soils in the Precambrian when due to various stresses on the surfaces of hard rocks the cryptic niches inside them were much more plausible habitats for organisms than epilithic ones. Using an actualistic approach we demonstrate that transformation of silicate rocks by endolithic organisms is one of the possible pathways for the beginning of soils on Earth. This process led to the formation of soil-like bodies on rocks in situ and contributed to the raise of complexity in subaerial geosystems. Endolithic systems of East Antarctica lack the noise from vascular plants and are among the best available natural models to explore organo-mineral interactions of a very old “phylogenetic age” (cyanobacteria-to-mineral, fungi-to-mineral, lichen-to-mineral). On the basis of our case study from East Antarctica we demonstrate that relatively simple endolithic systems of microbial and/or cryptogamic origin that exist and replicate on Earth over geological time scales employ the principles of organic matter stabilization strikingly similar to those known for modern full-scale soils of various climates.

The Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2 H -chromen-4-ol was studied in the presence of natural layered aluminosilicates modified by 0.5 mol/dm 3 HCl, such as montmorillonite, kaolin, and metakaolin obtained by the calcination of kaolin at 650 °C. According to infrared spectroscopy using pyridine as probe molecule, the amount and strength of Bronsted acid sites depend on the type of clay and decrease in the following order HCl-montmorillonite > HCl-kaolin > HCl-metakaolin. The difference in Bronsted acidity and textural properties of clays affected the reaction rate and the selectivity towards octahydro-2 H -chromen-4-ol.

The enthalpies of formation of natural trioctahedral smectite from elements were determined for the first time by high-temperature melt solution calorimetry using Tian-Calvet microcalorimeter: ΔfH0(298.15 K): −5799.1 ± 5.1 kJ/mol for saponite Ca0.1Na0.1K0.1(Mg2.6Fe0.12+Fe0.23+)[Si3.6Al0.4O10](OH)2 (Arkhangelsk diamond province) and −5937.3 ± 6.0 kJ/mol for saponite Ca0.4(Mg2.6Al0.2)[Si3.4Al0.6O10](OH)2 (Mt. Kukisvumchorr, Khibiny). The enthalpies of formation of magnesian and magnesium-iron saponites of theoretical composition were estimated.

The results of thermochemical studies are reported for nontronite samples from the Pinares-de-Majari (Eastern Cuba) (Sample I) and Kempirsai serpentine massif (South Urals, Kazakhstan) (Sample II). The enthalpies of formation of dehydrated hydroxyl-bearing nontronites from elements were determined by melt dissolution calorimetry using high-temperature heat-flux Tiana-Calvet microcalorimeter: Δ f H el o (298.15 K): −4958 ± 13 kJ/mol for Mg0.4(Fe 1.5 3+ Mg0.4Ni0.1)[Si3.7Al0.3O10](OH)2 (I) and −5003.6 ± 8.0 kJ/mol for Mg0.3Na0.1Ca0.1(Fe 1.4 3+ Mg0.5Ni0.1)[Si3.7Al0.3O10](OH)2 (II). It was determined experimentally that the enthalpy of dehydration (removal of molecular adsorption and interlayer water) of the studied nontronites is 6 ± 2 kJ per 1 mole H2O. The enthalpy of formation of nontronite of theoretical composition Mg0.15Fe 2 3+ [Si3.7Al0.3]O10(OH)2 was estimated at −4750 kJ/mol. The Gibbs free energies of formation of the nontronites were calculated.

Research on migration of chemical elements (ChEs) in soils is important for the understanding of geochemical processes in polluted and undisturbed landscapes. In this article, we report original data on Anthric Chernozems and Anthric Planosols within a small gully's catchment area in the Trans Urals (Russia). Mean total concentrations of 24 ChEs and content of mobile fractions (F1 – exchangeable, F2 – bound within organo-mineral complexes and F3 – bound with Fe and Mn hydroxides) of 61 ChEs including macro elements (Al, Ca, Fe, K, Mg, Mn, Na, P, Ti, S, Si), heavy metals (Ba, Co, Cr, Cu, Ni, Pb, Rb, Sr, Th, U, V, Zn), trace elements (Ag, As, B, Be, Bi, Br, Cd, Cs, Ge, Hf, Li, Mo, Nb, Pd, Sb, Sc, Se, Sn, Ta, Te, Tl, W, Zr) and rare earth elements (Ce, Er, Eu, Gd, La, Lu, Nd, Pr, Sm, Tb, Tm, Dy, Ho, Y, Yb) are determined from in a total of 60 samples from topsoil and subsoil of Anthric Chernozems and Anthric Planosols. The data obtained also include pH-value, total organic carbon content (TOC), seven particle-size classes (

The isotopic (U-Pb, 238U-235U, 234U-238U) and chemical study of whole-rock samples and finegrained fractions of rocks in a vertical section of the terrigenous sequence at the Dybryn uranium deposit in the Khiagda ore field shows that a wide U-Pb isotopic age range (26.9-6.5 Ma) is caused by oxidation and disturbance of the U-Pb isotopic system in combination with protracted uranium ore deposition. The oxidation of rocks resulted in the loss of uranium relative to lead and eventually to an overestimated 206Pb/238U age at sites with a low U content. The 238U/235U ratios in the studied samples are within the range of 137.74–137.88. Samples with a high uranium content are characterized by a decreasing 238U/235U ratio with a decrease in 207Pb/235U and 206Pb/238U ages. A nonequilibrium 234U/238U ratio in most studied samples furnishes evidence for young (

The paper reports results of an experimental thermochemical study (in a heat-flux Tian-Calvet microcalorimeter) of montmorillonite from (I) the Taganskoe and (II) Askanskoe deposits and (III) from the caldera of Uzon volcano, Kamchatka. The enthalpy of formation ΔfHel0 (298.15 K) of dehydrated hydroxyl-bearing montmorillonite was determined by melt solution calorimetry: −5677.6 ± 7.6 kJ/mol for Na0.3Ca0.1(Mg0.4Al1.6)[Si3.9Al0.1O10](OH)2 (I), −5614.3 ± 7.0 kJ/mol for Na0.4K0.1(Ca0.1Mg0.3Al1.5Fe0.13+)[Si3.9Al0.1O10](OH)2 (II), −5719 ± 11 kJ/mol for K0.1Ca0.2Mg0.2(Mg0.6Al1.3Fe0.13+) [Si3.7Al0.3O10](OH)2 (III), and −6454 ± 11 kJ/mol for water-bearing montmorillonite (I) Na0.3Ca0.1(Mg0.4Al1.6)[Si3.9Al0.1O10](OH)2 · 2.6H2O. The paper reports estimated enthalpy of formation for the smectite end members of the theoretical composition of K-, Na-, Mg-, and Ca-montmorillonite and experimental data on the enthalpy of dehydration (14 ± 2 kJ per mole of H2O) and dehydroxylation (166 ± 10 kJ per mole of H2O) for Na-montmorillonite.

The effect of acid modification of a natural montmorillonite clay (MM) by HNO3 on the catalytic properties of MM from Dash-Salakhlinsk (Kazakhstan) has been investigated in the synthesis of solketal from glycerol and acetone in solvent free and acetonitrile media. HNO3 concentration allowed to control the chemical composition, the surface acidity, the porous structure of the acid-activated MMs and their catalytic performance. The main reaction product was solketal with 86.6–98% selectivity. Conversion of glycerol depended on the Bronsted acidity. The most active sample, namely, MM activated with 0.5 mol/dm3 HNO3, showed good reusability for 3 catalyst cycles.

The paper discusses the mechanism of montmorillonite structure alteration and bentonites properties modification (on the example of samples from clay deposit Taganka, Kazakhstan) due to the thermochemical treatment (treatment with inorganic acid solutions at different temperatures, concentrations and reaction times). With the use of the suit of methods certain processes were distinguished: transformation of montmorillonite structure, which appears in the leaching of interlayer and octahedral cations, protonation of the interlayer and OH groups at octahedral sheets. Changes in the structure of the 2:1 layer of montmorillonite and its interlayer result in significant changes in the properties – reduction of cation exchange capacity and an increase of specific surface area. The results of the work showed that bentonite clays retain a significant portion of its adsorption properties even after the long term and intense thermochemical treatment (6M HNO3, 60°C, 108 hours)

First-ever ice core drilling at Mt. Kazbek (Caucasus Mountains) took place in the summer of 2014. A shallow ice core (18 m) was extracted from a plateau at ~4500 m a.s.l. in the vicinity of the Mt. Kazbek summit (5033 m a.s.l.). A detailed radar survey showed that the maximum ice thickness at this location is ~250 m. Borehole temperature of −7 °C was measured at 10 m depth. The ice core was analyzed for oxygen and deuterium isotopes and dust concentration. From the observed seasonal cycle, it was determined that the ice core covers the time interval of 2009–2014, with a mean annual snow accumulation rate of 1800 mm w. eq. Multiple melt layers have been detected. δ18O values vary from −25 to −5‰. The dust content was determined using a particle sizing and counting analyzer. The dust layers were investigated using scanning electron microscopy and X-ray diffraction analysis. Dust can be separated into two categories by its origin: local and distant. Samples reflecting predominantly local origin consisted mainly of magmatic rocks, while clay minerals were a characteristic of dust carried over large distances, from the deserts of the Middle East and Sahara. The calculated average dust flux over three years at Kazbek was of 1.3 mg/cm2 a−1. Neither δ18O nor dust records appear to have been affected by summer melting. Overall, the conditions on Kazbek plateau and the available data suggest that the area offers good prospects of future deep drilling in order to obtain a unique environmental record.

The chemical-mineral composition and morphological features of mineral nanoparticles of clay soils have been studied. In the clay soils of the Moscow moraine, nanoparticles are found to be localized in the surface microcavities of sand and silt grains covered with clay films. They have predominantly anisometric configurations and comprise mainly mixed-layered clay minerals and ferric oxides. The distinctive features of mineral nanoparticles are the high levels of specific surface and cation exchange capacity.

The solubility of ZrO2(baddeleyite) in HCl, HF, H2SO4, NaOH, and Na2CO3 solutions was determined by the capsule method at 500°C and 1000 bar. Baddeleyite is the only solid phase detected in the experimental products. Based on the ZrO2(baddeleyite) solubility measurements, the values of equilibrium constants at 500°C and 1000 bar (consistent with the Gibbs free energies of all the reactants) were obtained for the following reactions: ZrO2(cr) + H2SO 4 0 = Zr(OH)2OH 4 0 (pKo = 4.95), ZrO2(cr) + 2H2SO 4 0 = Zr(SO4) 2 0 ) + 2H2O (pKo = 3.74), ZrO2(cr) + H2O + HF0 = Zr(OH)3F0 (pKo = 3.35), ZrO2(cr) + 2HF0 = Zr(OH)2F 2 0 (pKo = 2.37), and ZrO2(cr) + 2H2O + OH− = Zr(OH) 5 − (pKo = 4.39). Ionization constants were estimated for the chloride, fluoride, sulfate, and hydroxo complexes of zirconium. Using the experimental data and thermodynamic information derived from experiments and the electrostatic model of the ionization of electrolytes, it was shown that no more than n mg zirconium per one kilogram H2O can be accumulated in high-temperature fluids at 500°C and 1000 bar.

Filtration-capacity properties of terrigenous reservoir rocks significantly depend on catagenetic transformations of clay minerals. Results of our research revealed the authigenic nature and formation stages of kaolinite and chlorite. The volume and shape of pore space define the morphology of clay particles. Depending on the pore volume, kaolinite crystallizes either as thick tabular aggregates or as fan-shaped intergrowths. The formation of authigenic clays in pores of terrigenous reservoirs decreases filtration-capacity properties of rocks with low permeability and, conversely, increases filtration-capacity properties of rocks with high primary permeability and large pore volume.

Two bottom sediment cores (BP00-23/7 and BP00-7/6) recovered from the Yenisei transect in the southern Kara Sea are described. Data on their grain size composition, clay and heavy mineral assemblages, and distribution of a large group of chemical elements are presented. Radiocarbon dates based on AMS C-14 method suggest the Holocene age of sediments in the cores. Literature data on physical properties and foraminifers have also been analyzed. The facies affiliation of the lithostratigraphic subdivisions has been unraveled. History of the Yenisei River runoff in the Holocene has been reconstructed on the basis of different indicators.

Integrated geological and geophysical investigation of bottom sediments in the Medvezhii Island region, southwestern margin of the Barents Sea, has made it possible to characterize sediments of diverse types related to the action of hydrocarbon fluids, hemipelagic sedimentation, slope phenomena, and combined influence of all these factors. Relatively homogeneous (in terms of mechanical composition) sediments are subdivided into several lithogenetic types based on the grain size distribution. Relationships of clay minerals, as well as their morphological and structural peculiarities, are described for each type. It is demonstrated that sediments formed under the substantial influence of hydrocarbon fluid fluxes are characterized by a high (relative to hemipelagic sediments) content of smectites and mixed-layer clay minerals of the illite–smectite series. It is assumed that these minerals are authigenic formations in mud volcanic rocks and diapir material. Based on the comparison of clay minerals contents primary source of the material for redeposited sediments has been reconstructed.

Two calcium-rich natural layered aluminosilicates containing 90–95 wt.% montmorillonite were chemically activated using 0.125–3.0 M HCl solutions. Structural and textural properties were characterized by X-ray diffraction, elemental analysis and N 2 -adsorption/desorption analyses. According to infrared spectroscopy using pyridine as probe molecule, the amount of Bronsted acid sites increased when increasing HCl concentration. The catalytic performance of these materials was investigated in the Prins cyclization of (−)-isopulegol with vanillin to form octahydro-2 H -chromen-4-ol, carried out in toluene at 35 °C. It was found that the amount of Bronsted acid sites and the microporosity of the catalysts are key factors for the control of the reaction rate and the selectivity towards octahydro-2 H -chromen-4-ol.

This paper discusses the mechanism of montmorillonite structural alteration and modification of bentonites’ properties (based on samples from clay deposits Taganskoye, Kazakhstan and Mukhortala, Buriatia) under thermochemical treatment (treatment with inorganic acid solutions at different temperatures, concentrations and reaction times). Treatment conditions were chosen according to those accepted in chemical industry for obtaining acid modified clays as catalysts or sorbents. Also, more intense treatment was carried out to simulate possible influence at the liquid radioactive site repositories. A series of methods was used: XRD, FTIR, ICP-AES, TEM, nitrogen adsorption, and particle size analysis. It allowed revealing certain processes: transformation of montmorillonite structure which appears in the leaching of interlayer and octahedral cations and protonation of the interlayer and –OH groups at octahedral sheets. In turn, changes in the structure of the 2:1 layer of montmorillonite and its interlayer result in significant alterations in the properties: reduction of cation exchange capacity and an increase of specific surface area. Acid treatment also leads to a redistribution of particle sizes and changes the pore system. The results of the work showed that bentonite clays retain a significant portion of their adsorption properties even after a prolonged and intense thermochemical treatment (1 M HNO3, 60 °C, 108 h).