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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.

—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.

Bentonite clay is an important natural material, widely used in many industries. The purpose of this article is to analyze the mineral resource base of bentonite clays in Russia. The data on reserves of deposits, the degree of their development and production volumes are given. The composition and uses of the main developed deposits of bentonite clay in Russia are characterized. A comparative analysis of the reserves and production growth of bentonite over the past decade is carried out. A brief description of the world situation is given, and the mineral resource base of the CIS countries is considered. Since the quality of raw materials, its properties and reserves directly depend on the conditions of origin, a characteristic of the geological and tectonic position and genesis of the bentonite clay deposits of Russia is given. Bentonite-bearing provinces with favorable conditions for the formation of bentonite deposits with volcanogenic-sedimentary genesis are considered. The most promising regions are proposed for the purposes of expanding the mineral resource base of bentonite materials. This work is the result of the authors’ own geological works at various deposits of bentonite clays in Russia, the near and far abroad, as well as the study and interpretation of published materials on this subject over the past decades.

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.

Bentonites from the 10th Khutor deposit (Republic of Khakassia, Russia) are considered a potential buffer material for isolation of radioactive waste in the crystalline rocks of Yeniseyskiy site (Krasnoyarskiy region). This study presents the results of a series of permeameter experiments with bentonite compacted to dry densities of 1.4, 1.6, and 1.8 g/cm3, saturated and permeated by the artificial groundwater from Yeniseyskiy Site. Permeation was conducted at hydraulic gradients of 180–80,000 m/m to simulate potential hydraulic conditions in the early post-closure phase of a deep geological repository (DGR). The respective swelling pressures of 0.8 ± 0.3, 2.2 ± 0.6, and 6.3 ± 0.3 MPa and permeabilities of (27 ± 15) × 10−20, (3.4 ± 0.8) × 10−20, and (0.96 ± 0.26) × 10−20 m2 were observed for the hydraulic gradient of 2000 m/m, which is recommended for the determination of undisturbed swelling pressures and permeabilities in permeameter experiments. Upon incremental increases in the hydraulic gradient, swelling pressures at all densities and permeability at the density of 1.8 g/cm3 remained unchanged, whereas permeabilities at 1.4 and 1.6 g/cm3 decreased overall by a factor of approximately 5 and 1.7, respectively. Seepage-induced consolidation and/or reorganisation of bentonite microstructure are considered possible reasons for these decreases.

The sorption of Cu2+ onto bentonite modified with Al Keggin cations and humic acid from CuCl2 solutions at pH 4.5 was studied. Modification of Na-bentonite with Al Keggin cations was found to result in an increase in the basal spacing of montmorillonite from 1.29 nm for N-form to 1.85 and 1.78 nm for HAl13 and Al13 forms respectively, in a reduction of CEC (cation exchange capacity) and in the formation of additional sites with a variable charge with pHPZC 4.2. Al13-bentonite is not affected by heat. Under the conditions of the experiments at pH of 4.5 Na-bentonite adsorbs more Cu2+ from CuCl2 solutions then Al13 forms of bentonites. The main mechanism of copper sorption on Na-bentonite is the cation exchange Cu2+&ndash, Na+. The reduction of CEC of Na-bentonite after modification with Al Keggin cations leads to a decrease in the Cu2+ sorption. pH-dependent sorption sites on Al13-bentonites have a pHPZC of 4.2 and, therefore, under conditions of the experiment have positive charge which prevents Cu2+ sorption. Na-bentonite adsorbs more humic acid solution (HA) then Al13-bentonite and the proportion of adsorbed HA remains constant over the entire concentration range. Treatment of the Al13-bentonite with HA leads to the formation of the additional sorption sites. The amount of sorbed Cu2+ and the percentage of their extraction from solutions by HAAl13-bentonite is similar to those values for Na-bentonite.

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.

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.

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.

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 aim of this study was to investigate the correlation between the basic and catalytic properties of brucite and Mg,Al-layered double hydroxides (Mg,Al-LDHs) in the reaction of propylene oxide with methanol. The basic properties of the solids were investigated by FT-IR spectroscopy using CDCl3 as probe molecule and Hammett acidity titration with n-butylamine and benzoic acid. Both the increase in the activation temperature and the decrease in Al content favored the increase in the basicity of Mg,Al-LDH. The nature of “Mn+ O2− Lewis acid-base” pairs was a key factor to control the catalytic behavior of the solids. The length of the M-O bond, the basicity of the oxygen ion and the strength of the metal ion on the surface affected the catalytic activity of the solids and their isomer selectivity in the reaction between methanol and propylene oxide to form 1-methoxy-2-propanol. It was demonstrated that brucite(150) can be applied as catalyst for at least four successive cycles without loss of activity.

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).