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Ion composition in groundwater at the spent nuclear fuel repositories is a relevant uncertainty for predicting the shear behavior of the bentonite buffer. However, only a few studies investigated the range of shear strength variation with in-situ groundwater conditions. This paper examines the ultimate shear strength of compacted Wyoming-type bentonite, focusing on the effect of pore water salinity. Triaxial tests were performed under effective confining pressures up to 10 MPa with different types of pore water representing: 1) extremely low, 2) current, and 3) maximal salinity conditions at the repositories, while tracking the evolution of exchangeable cation composition. The results revealed that pore waters with typical Ca2+ concentrations at the repositories strengthen the sodium bentonite through Na+-Ca2+ cation exchange. The observed salinity-dependent strength of the bentonite was described by the ultimate shear strength line and its apparent mobilization in the deviatoric stress-mean effective stress plane. The upper limit of the increase in strength was found to be 0.74 MPa. Previous triaxial test results with deionized water were compared to refine the shape of the ultimate shear strength line. Lessons learned from the triaxial testing of saturated bentonite were elucidated to offer recommendations to address the challenges associated with high swelling potential and low permeability. The findings in this paper have implications for accurate assessment of shear behavior in the deep geological disposal system as well as effective laboratory measurements of the shear strength parameters of compacted bentonite. • Triaxial tests on a highly-swelling material under high confining pressure and pore water salinity are documented. • Shear strength dependency of a compacted bentonite on pore water salinity has been quantified. • Recommendations for triaxial testing of compacted bentonite are provided. [ABSTRACT FROM AUTHOR]

Selected layered clay minerals of smectite group with different chemical composition (e.g. synthetic hectorite, synthetic smectite and natural smectite) were modified by rare earth cations such as Er3+ and a stochiometric mixture of Er3+/Yb3+. Raw and modified smectites were systematically heated up to temperatures ensuring their dehydration (400 °C), dehydroxylation (800 °C) and formation of new high temperature phases (1200 °C). The products of heating were investigated by terahertz-time domain spectroscopy to follow changes of their dielectric properties in the far-infrared region. The frequency-dependent refractive index of raw and modified clays was determined in the range of 0.2–3.8 THz (6.6–126.5 cm−1). The heating at 800 °C and above resulted in increase frequency dependent index of refraction and decrease absorption coefficient in comparison to the raw clays. The ion-exchanged smectites by rare earth cations further decreased the absorption coefficient of the samples heated at 1200 °C. Raw natural smectite sample revealed a low frequency band at 0.86 THz, already reported in the literature, which shifted to 0.67 THz after sample modification by rare earth cations. Heating of modified JP to 1200 °C resolved a new absorption band at ∼3.40 THz in the ceramic phase produced from raw natural smectite. • Cation exchange reaction was used for modification of clays by selected rare earth elements. • Effect of sample heating up to 400, 800 and 1200 °C was studied. • Terahertz time domain spectroscopy was used to study the refractive index dispersion. • The frequency dependence of absorption in THz region resolved new typical absorption bands. • The high temperature treatment can be used for synthesis of new ceramic phosphor materials. [ABSTRACT FROM AUTHOR]

Geopolymers (GP) are ceramic-like materials that can potentially be used in environmental applications to immobilize radionuclides (RNs) or toxic compounds. Although the literature reports that the sorption potential of a GP is influenced by its sorption capacity, especially for GPs produced from metakaolin (MK), the RN sorption mechanisms of these materials must be comprehensively studied together with their surface properties. In this study, the surface properties of a sodium-alkalinized MK-based GP (Na-MKGP), such as its surface protonation and cation exchange capacity (CEC), were characterized, and the sorption mechanisms of cesium (Cs+), strontium (Sr2+), and europium (Eu3+), which are important RNs for the safety assessment of high-level radioactive waste disposal, as functions of pH, ionic strength, and metal-ion concentration were investigated. The results were evaluated using the "two-site proteolysis no-electrostatics surface complexation/cation exchange (2SPNE SC/CE)" model by optimizing the selectivity coefficients and SC constants of the metal ions. Overall, this study provides a way to model the sorption of various cations to GP by a mechanistic model as is the case for clay minerals and makes the use of GP as a matrix of radioactive waste more attractive. • Cs+, Sr2+, Eu3+sorb on sodium alkalinized metakaolin-based geopolymer (Na-MKGP) by cation exchange and surface complexation, like as clay minerals. • Silicate plays significant role on europium sorption. • The distribution ratio of the sorbed metal ions modeled the selectivity coefficients and surface complexation constants are and optimized. • Surface deprotonation trend showed the point of zero charge of Na-MKGP is approximately pH 5.3. • Washing and drying improve the cation exchange capacity of Na-MKGP. [ABSTRACT FROM AUTHOR]

The presence of antibiotics in soil and water raises great health concerns because they may increase the development of harmful antibiotic-resistant bacteria. In this study, composite beads prepared from 2:1 or 1:1 ratios of montmorillonite (Mt) and sodium alginate (SA) were used to adsorb tetracycline hydrochloride (TC), an antibiotic commonly found in aqueous systems. The equilibrium time for TC adsorption onto the Mt/SA was 8 h, and the kinetic data were consistent with the pseudo-second-order model. The adsorption isotherm was described with the Langmuir equation. The maximum amounts of TC adsorbed were 745, 689, and 445 mg g−1 for the 2:1- and 1:1-Mt/SA and the original Mt, respectively. The Mt/SA composite beads exhibited porous structures; however, this did not play a key role in TC removal, as previously reported. Cation exchange was the major adsorption mechanism, and electrostatic attraction and hydrogen bonding between the SA and TC also contributed to TC adsorption on the Mt/SA composite beads. In addition, the migration of a small amount of TC into the inner spaces of the beads led to the intercalation of the TC in the Mt interlayers and enhanced TC adsorption by the Mt/SA composite beads. • The porous structures of composite beads adsorbed remarkable amounts of tetracycline (TC) from water. • Cation exchange was the primary adsorption mechanism of TC. • Electrostatic attraction and hydrogen bonding between alginate and TC enhance TC adsorption. • The amine and dimethylamino groups of TC orient horizontally on the internal surface of composite beads. [ABSTRACT FROM AUTHOR]

Clay minerals, as biofriendly and low-cost materials, are highly essential for the modern industrial applications including the production of clean energy, its storage and conversion. Here, the capabilities of pure and cation exchanged rectorite, a regularly interstratified phyllosilicate from Beatrix Mine (South Africa) were explored and discussed. A comprehensive characterization was performed by means of high resolution solid-state NMR, electrochemical impedance spectroscopy and powder X-ray diffraction. 23Na MAS and 3QMAS NMR spectroscopy was used to characterize accessibility of interlayer space in rectorite for exchangeable cations. Three Na sites attributed to easily exchangeable Na+ on the surface or in large pores, Na+ in dehydrated micaceous interlayers and Na+ in hydrated smectite interlayers were identified. Differences in hydration states in smectitic interlayers depending on the type of intercalation were detected using 1H MAS NMR. A higher amount of hydrating water molecules in pure and Mg-exchanged rectorites was attributed to the higher hydration energy of Ca2+ and Mg2+. The temperature dependences of electrical conductivity in this work were best described using the empirical Vogel-Tammann-Fulcher equation with the temperature-dependent effective activation energy parameter. Significantly stronger change of activation energy in Mg2+ exchanged rectorite in the temperature range of 10 °C to 50 °C as compared to pure rectorite and its Na+, Li+ and NH 4 + modifications was related to an extensive H-bond network in the interlayers, which facilitated an effective proton transfer responsible for electric conductivity. The obtained resutls suggested a greater potential for the use of Mg-exchanged rectorite as ionic conductor at enhanced temperatures. [Display omitted] • Rectorite from Beatrix Mine was studied towards the structure – conducting properties relation. • Accessibility of interlayer space for exchangeable cations was characterized by solid state NMR. • Electrical conductivity in rectorite depends on interlayer cations, hydration and temperature. • Conductivity originates from proton transfer over the hydrating water network in the interlayers. • Mg-exchanged rectorite has a great potential as ionic conductor at enhanced temperatures. [ABSTRACT FROM AUTHOR]

A series of organoclays were synthesized by modifying bentonite with lecithin under two pH reaction solutions, one acid and one basic. The products prepared using various surfactant concentrations (0.2–5.0CEC) were characterized by multiple experimental techniques. The conformational arrangement of the loaded surfactant, as well as the fluctuation in lecithin molecular properties and interlayer cation content in the organoclay were evaluated. According to the experimental results, the conformation of lecithin in the organoclay interlayer space undergoes a transition from flat-lying layer to a tilted paraffin-type-bilayer. This phenomenon happens for both pH but, interestingly, follows two different mechanisms. It can be observed that the cations content decreased during the addition of lecithin at pH = 1.0, suggesting that the surfactant intercalated into the interlayer space through cation exchange. On the contrary at pH = 9.0, the zwitterionic nature of lecithin allowed its intercalation in the interlayer space via ion-dipole interactions with the cations. Compared with the organoclay prepared at pH = 1.0, the organoclay prepared at pH = 9.0 also exhibited weaker hydrophobicity, clearly reflecting the difference in the interlayer conformation. [Display omitted] • The properties of organoclays prepared from lecithin-modified bentonite are pH dependent. • The lecithin conformationundergoes a transition from lying layer to a tilted paraffin-type-bilayer • The intercalation mechanism is cation exchange（pH = 1.0）while ion-dipole interactions （pH = 9.0）. [ABSTRACT FROM AUTHOR]

Perfluorooctanesulfonate (PFOS) is a hazardous chemical, and its presence in surface and groundwater poses a risk to environmental quality and human health. Containment is often applied to immobilize PFOS to stop or minimize the exposure. Mineral-based materials became promising adsorbents. However, there is scope to develop adsorbents using locally available minerals and understand their adsorption mechanisms. Here, we developed oleylamine-modified composites using naturally occurring Iranian zeolite and diatomaceous earth (DE). The mineralogy and surface properties of materials were fully characterized, and the adsorption of PFOS from simulated wastewater was linked to it. Clinoptilolite in zeolite sample, calcite and kaolinite in DE were main mineral assemblages. The raw samples also contained silica as a main constituent of them. Thermogravimetric analysis suggested that the materials were successfully modified with the oleylamine molecules in the material's structure and surfaces. These were further supported by scanning electronic microscopy (SEM), Fourier transmission infrared spectroscopy (FTIR), and surface and pore size analysis. After adsorption at various pHs, the isotherm of adsorption was also performed at ambient temperature. Modified DE and zeolite tend to adsorb PFOS (14.1 and 25.5 mg/g, respectively) more than their raw counterparts (4.72 and 0.39 mg/g, respectively). Adsorption models suggest monolayer and, in rare cases multilayer binding capacities and affinities toward PFOS. We analyzed the post-adsorption materials and discovered that electrostatic and hydrophobic interaction was likely the main cause of PFOS adsorbed to the material. This research helps to improve our knowledge of how PFOS adheres to untreated and surfactant-altered zeolite and DE in aquatic environments. [Display omitted] • Locally sourced Iranian zeolite and diatomite characterized mineralogically. • Materials modified with primary amine (oleylamine) without prior processing • Perfluorooctane sulfonate (PFOS) was removed from water by the modified minerals. • Amine-modified zeolite appears to be low cost and efficient adsorbent for PFOS. • Mechanistic study suggests adsorbent removed PFOS electrostatically and hydrophobically. [ABSTRACT FROM AUTHOR]

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 NaClO 4), 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). Unlabelled Image • Sorption of Eu(III) onto previously not studied montmorillonite is investigated. • Samples include new Kutch bentonite from India and Khakassia bentonite from Russia. • Admixture iron oxyhydroxide in Kutch bentonite influences Eu(III) sorption. • Thermodynamic model describing Eu(III)–montmorillonite interaction is proposed. • The constant for ion-exchange Eu(III) reaction with montmorillonite is calculated. [ABSTRACT FROM AUTHOR]

Abstract Highly water-soluble material of multi-imidazolium based silsesquioxane cages (material 2) is a promising candidate for modifying clay mineral interlayer space, which is successfully demonstrated by using montmorillonite. The modified montmorillonite can be easily prepared via cation exchange reaction between material 2 and sodium ions of montmorillonite, dispersed in an aqueous solution at room temperature. The modified montmorillonite formed a precipitate within a few seconds. A single layer of material 2 found to be intercalated in the modified montmorillonite with a maximum interlayer space (d -value) of 18 Å (1.8 nm) from 13 Å (1.3 nm) of the unmodified one was confirmed by transmission electron microscopy (TEM) and X-rays diffraction (XRD). Moreover, the percentage uptake and nature of incorporation of material 2 into montmorillonite layers were investigated by thermal gravimetric analyses (TGA), 29Si NMR and FT-IR spectroscopies. Graphical abstract Unlabelled Image Highlights • POSS-based ionic materials adsorbed on montmorillonite by the cation exchange. • Hydrophobically modified montmorillonite formed precipitates in aqueous solution. • The d -value of modified montmorillonite was extended by about 5 Å. • The extended spacing confirmed the presence of POSS molecules in single interlayer. [ABSTRACT FROM AUTHOR]

Abstract The possibilities of exchange reactions in two types of layer Zn-hydroxy sulfate minerals with neutral and negatively charged hydroxide layer – namuwite (Zn 4 (OH) 6 (SO 4)·4H 2 O) and gordaite (NaZn 4 (OH) 6 (SO 4)Cl·6H 2 O) – were studied. As starting materials, synthetic analogs of these minerals are used. Through direct synthesis, besides the known namuwite, gordaite, and its Ca2+ form, a series of new cationic (K+, NH 4 +) and anionic (Cl− and Br−) gordaite forms were synthesized. The K+, NH 4 + content is respectively about 1/3 and 2/3 of the nominal compositions. The determined characteristics of Br-forms showed similarity with corresponding chloride forms. The results of the experimental study of the interaction between gordaites and namuwite and various halide solutions showed the realization of three types of solid-state exchange reactions: cation exchange, simultaneous cation-anion exchange, and water molecule-halide anion exchange. All samples were characterized by powder XRD and EDS chemical analysis, and the transformation mechanism was monitored by SEM investigation. By cation exchange, the all cationic gordaite forms were formed, and in addition, Sr2+-form was also obtained. Mutual conversions between the isovalent cations Na+-K+, Ca2+-Sr2+, and between all possible combinations of heterovalent cation pairs were established. Regardless of the charge of the hydroxide layer – neutral (namuwite) or negatively charged (gordaites), due to the stronger interaction of halide anion with the interlayer cations than that with the hydroxide layer's tetrahedral Zn2+ cation, the anion exit together with the leaving cations was observed, causing the simultaneous cation-anion exchange or mutual substitution of H 2 O molecules and halide anions. In the first case, the gordaite Br-forms from chloride one are formed. However, under treatment of the all various gordaite forms with iodide solutions, no exchange was observed. The big size of I− anion probably prevents its occupation of the apical position of hydroxide layer's Zn-tetrahedron and provokes the formation of new pure zinc-hydroxy-sulfate-hydrate phase with unknown specific structure. In the second case, the solid-state mutual substitution of H 2 O molecules and halide anions halide in the apex of the Zn-tetrahedron resulted in the formation of different zinc hydroxy sulfate hydrates, depending on the treating water amount. The reversible reaction caused a formation of different cationic gordaite forms under treatment of namuwite with chloride solutions of Na+, K+, NH 4 +, Ca2+, and Sr2+. The treatment of gordaites and namuwite with chloride solutions of some of the other alkaline and alkaline earth metals Li+, Mg2+, and Ba2+ resulted in gordaite dissolution and subsequent pseudomorphic simonkolleite crystallization. The simonkolleite formation is probably due to geometric difficulties for Li+ and Mg2+ interlayer incorporation caused by their great hydration capability and for Ba2+ due to its ability to form insoluble barite. Highlights • Three types of exchange reactions (cation, simultaneous cation-anion, and H 2 O-halide anion) occur • The specific structural position of halide anion (or H 2 O) predetermines the possibilities of exchange reactions • The cationic (Na+, K+, NH 4 +, Ca2+, and Sr2+) and anionic (Br−) gordaite forms were obtained by the exchange reactions [ABSTRACT FROM AUTHOR]

Abstract Montmorillonite (Mt) is well known as reinforcing agent in films. Moreover, it stabilizes anthocyanin pigments. In this study, Mt has been added as both reinforcement and color stabilizer to gelatin films containing acerola juice. Films were produced with different Mt concentrations (0–6.5% on gelatin). Increasing Mt contents resulted in enhanced tensile strength and modulus, although the elongation has been decreased. Mt also reduced the water vapor permeability in up to 45%. Mt presented two effects on film color: first, it changed its color from yellowish to red; and second, it stabilized film color throughout storage, mainly when added at 3.9%. It has been suggested that metals from Mt (such as Fe3+ or Al3+) may have formed complexes to anthocyanins, changing and stabilizing their color. Graphical abstract Unlabelled Image Highlights • Acerola juice-gelatin films were produced with 0–6.5% montmorillonite (Mt). • Mt enhanced tensile and water vapor barrier properties of films. • Mt addition resulted in film color shift from yellowish to red. • Mt also stabilized film color throughout storage, mainly at 3.9%. [ABSTRACT FROM AUTHOR]

This research presented six natural clay minerals (NCM) evaluated for the effectiveness of NH 4 + adsorption from aqueous solution. For the first time, the NH 4 + adsorption capacities of kaolinite, halloysite, montmorillonite, vermiculite, palygorskite, and sepiolite were examined and compared in the same study. All the NCM were fully characterized by XRD, SEM/EDS, XRF,FTIR, CEC, zeta potential and nitrogen adsorption-desorption isotherms to better understand the adsorption mechanism-property relationship. Adsorption kinetics showed that the adsorption behavior followed the pseudo-second-order kinetic model. The adsorption isotherms fitted by the Langmuir model illustrated that among all the NCM studied, vermiculite (50.06 mg/g) and montmorillonite (40.84 mg/g) showed the highest ammonium adsorption capacities. Our results revealed that the cation exchange is the main mechanism for the NH 4 + adsorption. Additionally, negatively charged surface, water absorption process and surface morphology of NCM might also contribute to the high adsorption capacity for the NH 4 + . The maximum adsorption capacities for all NCM were rapidly obtained within 30 min with a dosage of 0.3 g/25 mL at pH of 7. The results illustrated that the NCM have significant potential as economic, safe and effective adsorbent materials for the NH 4 + adsorption from the aqueous solution. [ABSTRACT FROM AUTHOR]

Bentonites are considered as an engineered barrier for a high-level radioactive waste (HLRW) repository. The Czech product Bentonite 75 is a potential candidate material to be used as a buffer and a backfill. The bentonite barrier is supposed to undergo alteration and transformation processes due to reaction with groundwater and heating originated from radionuclide decay. Detailed knowledge of the bentonite-water interaction is a crucial issue for the evaluation of the long-term stability of the bentonite barrier. This study presents the results of a laboratory experiment in which the repository conditions, hydration, and heating of the bentonite were simulated. Bentonite 75 reacted in a closed system with demineralised water and groundwater at 90 °C for 2 years. Bentonite material (solid phase) and aqueous extracts were analysed over time with respect to the mineralogical and chemical changes. The results indicate that montmorillonite alteration, particularly illitization, could be excluded in this system due to the low concentration of K + in the solution. In addition, cation exchange capacity measurements did not indicate any transformation process of montmorillonite. Slight modifications of montmorillonite basal reflection profiles in PXRD patterns were attributed to cation exchange reactions. The most reactive minerals included siderite, Fe-dolomite/ankerite, and calcite/Mg-calcite. Dissolution/precipitation of these minerals controlled the composition of the aqueous phase that affected the distribution of the exchangeable cations in the montmorillonite interlayer. The most significant change was the dissolution of siderite that induced partial dissolution of calcite, which resulted in the replacement of Na + and Mg 2 + by Ca 2 + . The overall evolution of the water chemical composition could be predominantly explained by mineral phase equilibria. The initial water composition did not affect the geochemical processes, which took place in the bentonite-water system due to the strong buffering bentonite capacity. [ABSTRACT FROM AUTHOR]

In China, GMZ bentonite has been recognized as the first choice of buffer material while Beishan area in Gansu province has been considered as the potential disposal site for high-level radioactive waste (HLW) repository. As the groundwater at the repository field is rich in Na + and Ca 2 + , the swelling properties of compacted GMZ bentonite will be affected by the chemistry of groundwater. In this work, the swelling deformation behaviors of compacted GMZ bentonite were tested at a vertical stress of 0.1 MPa to assess the influence of cation exchange between Na + and Ca 2 + , as well as the salinization-desalinization effect by cyclical infiltrations of distilled water and saline solutions. Results show that Na-bentonite is partly transformed into Ca-bentonite once NaCl solution is replaced with CaCl 2 solution. Comparing to NaCl solution, the inhibiting effect of CaCl 2 solution is weak, and thus the additional swelling is observed. Along with chemical cycles, the total strain of compacted GMZ bentonite gradually increases, while the chemical sensitivity of strain behavior reduces. This tendency is also detected for GMZ bentonite experiencing the desalinization path of distilled water prior to each infiltration of salt solution. Regarding the relative strain of GMZ bentonite, the difference in osmotic suction between distilled water and salt solution is more relevant than the sodium-calcium replacement. [ABSTRACT FROM AUTHOR]

This paper implements hydrophobic modified clay layers with ammonia salts (Organoclay) using ultra-sonication and water as a solvent to develop functional clay/Poly vinyl alcohol (PVA) aerogel composites through an environmentally friendly freeze drying process. Various compositions have been designed aiming at the high effectiveness of reducing moisture absorption while increasing the structural integrity and overall compressive modulus but reducing the thermal conductivity of the aerogel composites. The results showed significant enhancement to both physical and mechanical properties of the aerogel composites. The microstructure systems of the aerogel composites could be tailored to result in multifunctional performance for the targeted applications. The moisture absorption could be reduced five folds compared to that of normal clay aerogels depending on the exposure relative humidity. While the modulus of the aerogel composites was doubled from an initial modulus of 0.39 to 0.82 MPa, the thermal conductivity was reduced by up 20% reaching values as low as 0.0315 w/mk. These aerogel composites could be an effective and efficient thermal insulation material to be implemented in the construction industry. [ABSTRACT FROM AUTHOR]

Polyether amine (PA) has recently been widely applied in water-based drilling fluid to improve shale stability. To study whether PA intercalation and the resulting increase of montmorillonite (Mt) d001-value have a negative effect on shale stability, a PA adsorption test on shale, a shale composites X-ray diffraction (XRD) test and a one dimensional swelling test of shale immersed in solution were conducted. PA can absorb on shale by exchanging Na + in shale, resulting in a d001-value increase of sodium montmorillonite (Na-Mt) in shale and large vertical displacements, causing lots of micro cracks to develop in the shale with the shale matrix dispersed. For shale immersed in solution with KCl and PA mixed, PA intercalation was reduced and even prevented because K + can exchange Na + in the shale first. With the cation hydration reduced by K + adsorption and the clay layer hydration decreased by PA adsorption on clay layer, vertical displacement was greatly reduced and stability was greatly enhanced for the shale immersed in solution with KCl and PA mixed. As a result, during drilling in shale containing Na-Mt, PA can cause shale instability. Using PA and KCl together can achieve better shale stability compared to using KCl only. [ABSTRACT FROM AUTHOR]

This work reports a detailed study of the K-, Mg-, and Ca-magadiites simulated from the structure of Na-magadiite. Several molecular geometries were tested in each model, and the results showed a hydration sphere similar to the initial sodium material. In the interlayer region, Na- and K-magadiites showed longer coordinated bond lengths, leading to higher basal spacing values (15.43 Å and 15.71 Å, respectively). Solids containing divalent cations presented the strongest H-bonds between the water molecules and the layers, also reinforced by the charge density distribution. Different stretching (3000 − 3800 cm−1) and bending (1500 − 1750 cm−1) of water molecules were identified in the vibrational analysis, and the simulated-experimental comparison of spectra suggested that dehydrated samples adsorb water molecules initially in axial positions and, later, in equatorial positions. Thermodynamics analysis at 298.15 K confirmed the difficulty of obtaining complete sodium to potassium exchanged forms (Δ G = 126.03 kJ.mol−1), while Ca-magadiite can be formed spontaneously (Δ G = −190.86 kJ.mol−1). • The cation-exchanged magadiites have been simulated by DFT calculations. • K-, Ca- and Mg-magadiite showed geometry coordination similar to Na-magadiite. • Hydrogen bonds and the hydration sphere of each model described their respective interlayer space. • Two positions of water molecules have been identified during the adsorption process. [ABSTRACT FROM AUTHOR]

Infrared Spectroscopy is a very useful tool studying clay minerals in a structural level as well as interactions on their surfaces. In this study, middle- and far- infrared spectroscopy was utilised to better understand how iron-bearing smectites and more specifically the nontronite-1 (NAu1) alters upon iron reduction. Changes in the middle-infrared spectral range have been studied extensively, such as the 3570 cm−1, 1020 cm−1 and 823 cm−1, while far-infrared spectral range changes have not drawn much attention. In this study, NAu1 spectra of oxidised, partially, and fully reduced state are presented noting the differences that occur on different vibration bands at this low frequency infrared range. Key changes took place at the region of 430–494 cm−1, as well as the 145 cm−1 band. From the 175 cm−1 to the 380 cm−1 region, vibrating bands disappeared or convoluted in a wider spectral envelope, upon full iron reduction. At the same time, NAu1 is saturated with different cations, such as Na+, Ca2+, K+, isolating effects on vibrating bands, depending on these cations, across the oxidation states and infrared range examined. These effects are more prominent at the region of 1620–1650 cm−1, where adsorbed H 2 O bending vibration takes place, for the middle-infrared range. Far-infrared range changes, due to the cation present, are less prominent, but recorded and discussed in detail. Eventually, the redox state of iron-bearing clay minerals controls the structural configuration of the lattice and consequently the interaction strength of clay mineral/saturating cations. The increasing interaction strength observed was Ca2+ < Na+ < K+, which will govern clay mineral hydration and cation exchange processes taking place on the clay mineral surface, as demonstrated, and discussed in this study. These outcomes can be useful in agriculture, waste disposal, and the oil & gas industry. [Display omitted] • Mid- & Far- infrared spectra for nontronite at different oxidation/reduction states. • Oxidised and fully reduced Nontronite infrared spectra exhibited high dissimilarity. • Stronger clay mineral/cation interaction under partially and fully reduced state. • More cation hydration effects on mid- than far- infrared spectral range. [ABSTRACT FROM AUTHOR]

Raw montmorillonite (Mt) was cation-exchanged with Ca 2 + , Mg 2 + , and Fe 3 + , and Pb 2 + was tested for its adsorption on the exchanged Mt. The d-value and the cation exchange capacity (CEC) of Ca-exchanged montmorillonite (Ca 2 + + Mt) were larger than those of Mg-exchanged montmorillonite (Mg 2 + + Mt) and Fe-exchanged montmorillonite (Fe 3 + + Mt). The Pb 2 + adsorption on the homoionic Mt was fast and the amount of Pb 2 + adsorption followed the order of Ca 2 + + Mt > Mg 2 + + Mt > Fe 3 + + Mt. Simulation of Pb 2 + adsorption on the Mt revealed a much larger energy drop when Pb 2 + is substituting for Ca 2 + in comparison to Pb 2 + exchanging for Fe 3 + . [ABSTRACT FROM AUTHOR]

A research programme has been set up to investigate the sequence of physical and chemical reactions in compacted soil–lime mixtures and their influence on the mechanical and hydraulic performance with time. The paper illustrates a method set up to monitor sequence and development of soil–lime reactions with curing time based on pH measurement. The method was also used, together with SEM observations and chemical analyses, to properly analyse results of hydraulic conductivity and oedometer tests performed on compacted soil–lime samples cured in saturated and unsaturated conditions. It was found that the hydraulic conductivity significantly decreases by increasing the time spent in unsaturated condition and it tends to appreciably reduce with time. In terms of compressibility, higher compression index resulted in saturated curing conditions. These differences were found to be due to a different microstructure. A crystalline, more brittle structure was detected in the case of immediate saturation with an ununiformed distribution in pore size. Unsaturated curing conditions give rise to amorphous, uniformly distributed pozzolanic products, with a more homogeneous pore size distribution. [ABSTRACT FROM AUTHOR]

Abstract: The removal of tetracycline (TC) from aqueous environment by illite (IMt-2) was studied in a batch system at different pH and ionic strength conditions. Adsorbent characterizations were determined by XRD and FTIR. The TC adsorption capacity on IMt-2 was 32mg/g at pH 5–6 and the adsorption equilibrium data obeyed the Freundlich isotherm. The kinetics of TC adsorption was moderately fast and almost reached equilibrium in 8h and the results followed pseudo-second-order kinetic model and Elovich model. The X-ray diffraction patterns before and after TC adsorption revealed no changes in basal spacing and intensity under two kinetic adsorption and a few initial TC concentration conditions, indicating that the adsorbed TC molecules were on the external surface of the mineral in contrast to intercalation of TC into swelling clay minerals, such as montmorillonite and rectorite. In spite of its low TC adsorption capacity, the results suggested that IMt-2 could be a good candidate to remove TC from wastewater containing higher amounts of TC and illite would be an important environmental sink for the fate and transport of TC in soils. [Copyright &y& Elsevier]

Abstract: The intercalation of nickel and cobalt thiabendazole complexes into montmorillonite was investigated by two strategies. The first strategy consisted of exchanging sodium montmorillonite (Na+–Mt) by nickel or cobalt ions followed by complexation of these cations by thiabendazole. The second method was the direct exchange of the sodium ions by the Ni– or Co–thiabendazole complexes. The thiabendazole–montmorillonite complexes were investigated by X-ray diffraction, FTIR and TGA analysis. [Copyright &y& Elsevier]

Abstract: Frequent detection of antibiotics in natural environment and wastewater effluent requires systematic investigations of various clay minerals. Dioctahedral 2:1 clay minerals are major constituents of soil and sediments. Interaction of these clay minerals and ciprofloxacin (CIP) was studied. The CIP adsorption capacities on montmorillonite, rectorite, and illite were 1.19, 0.41, and 0.10mmol/g, corresponding to 1.0, 1.0, and 0.9 CEC. Desorption of the equivalent amounts of exchangeable cations suggested that the cation exchange was mainly responsible for the CIP adsorption on montmorillonite and rectorite. The expansion of the basal spacing and shifts of characteristic FTIR bands indicated the intercalation of CIP ions with tilted orientation in montmorillonite and rectorite. The displacement of exchangeable cations and associated FTIR band shifts also indicated the cation exchange as important for CIP adsorption on illite but hydrogen bonding between CIP carboxylic groups and basal oxygen atoms on external surface apparently made a significant contribution to the adsorption. [Copyright &y& Elsevier]

Abstract: An organo-montmorillonite (Cloisite® 30B) was modified with fluorescent dyes to obtain photo-functional inorganic–organic complexes for real-time monitoring of polymer-clay nanocomposite processing. The photo-functionalization with 9-anthracenemethanol (anth) was tested using adsorption from solution, as well as dry and melt compounding. Rhodamine 6G Perchlorate (RhP) and Nile Blue A Perchlorate (NBAP) were adsorbed by cation exchange. XRD, TGA and spectrofluorimetry showed that cation exchange in water/ethanol at 80°C, with an added amount of RhP corresponding to 25% of the initial surfactant content, followed by washing, recovering and drying, yielded the best results. The intercalation of the fluorescent dyes rearranged the paraffinic structure of the surfactant molecules by increasing the tilting angle from 37° to 49°. [ABSTRACT FROM AUTHOR]

Abstract: Fluoroquinolones are a group of antibiotics commonly used in human and veterinary medicine. Highly enriched in sewage sludge as well as animal manure they can enter the environment by surface application of the sludge and manure. In this study, the interaction and adsorptive removal of ciprofloxacin (CIP) with a sodium montmorillonite (MMT) were studied in batch tests and supplemented by XRD and FTIR analyses. The adsorption of CIP on MMT was instantaneous with a large rate constant and a high initial rate. Quantitative desorption of exchangeable cations confirmed cation exchange as the most important mechanism of CIP adsorption on MMT. Higher CIP adsorption was achieved when solution pH was less than the pKa2 value of CIP, above which adsorption coefficient decreased significantly. Fitting of experimental data to adsorption of different CIP species indicated that both cationic and zwitterion forms of CIP could adsorb on MMT. An increase in basal spacing after CIP uptake indicated interlayer adsorption, i.e. intercalation of CIP. The substantial adsorption of CIP when pH was greater than the pKa2 together with the disappearance of C=O stretching vibration of the –COOH group in FTIR analyses suggested that complexation may be the dominant mechanism at high pH. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports the structure of polyhedral oligomeric silsesquioxane (POSS)–octaammonium in the interlayer space of montmorillonite. The ion exchange reaction was conducted with a large excess of POSS and yielded which was investigated by EDX, XRD, FTIR and TGA coupled with GC/MS. All eight aminopropyl groups of cubic POSS were flexible enough to interact with the negative sites on montmorillonite yielding an alignment of the POSS in the interlayer space. POSS–MMT complex was calcinated and characterized by XRD. Since the basal spacing did not change, the calcinated MMT was supposed to be stabilized by polyhedral oligomeric silsesquioxane pillars. This kind of open and stable pillared structure can be useful for many applications such as new supports for catalysis. [Copyright &y& Elsevier]

Abstract: Zeolite N was produced from a variety of kaolinites and montmorillonites at low temperature (<100°C) in a constantly stirred reactor using potassic and potassic+sodic mother liquors with chloride or hydroxyl anions. Reactions were complete (>95% product) in less than 20h depending on initial batch composition and type of clay minerals. Zeolite N with 1.0

Abstract: Partial substitution of the interlayer cations of a local bentonite (Bogovina) by hexadecyl trimethylammonium ions (HDTMA) was performed to prepare adsorbents able to simultaneously adsorb toxic metal cations and organic pollutants. Acid Orange10 adsorption increased with increasing HDTMA addition, while the adsorption of Pb2+ decreased with increasing organophilicity. The adsorption of the dye and Pb2+ and their mixture onto Na-rich bentonite and HDTMA-bentonites, regardless of adsorbents'' organophilicity, obeyed the pseudo-second-order kinetics model. [Copyright &y& Elsevier]

Abstract: Highly saline solutions are expected to play an important role in long term safety assessment of bentonite buffer for storage of radioactive waste. Montmorillonites being the main components of bentonites are suspected to undergo mineral alteration (particularly illitization or related mineral alteration processes) upon reaction with highly saline solutions. Literature data, however, do not provide a homogenous picture, yet. Possible alteration mechanisms, therefore, are still under discussion. In the present study 36 bentonites from different deposit were reacted in a closed system with a 6 M NaCl solution at 60 °C for 5 months, respectively. Run products were washed and dialysed and finally analyzed with respect to chemical and mineralogical changes by XRF, XRD, CEC, water uptake capacity, and amount of soluble silica. All significant chemical changes could be explained by the expected cation exchange (Na+ for Ca2+/Mg2+). After the experiment, however, the exchange sites were not completely occupied by Na+ despite a 100 fold excess of Na+ compared to the CEC. The presence of carbonates, obviously, interferes with the exchange of Na+ for Ca2+/Mg2+. The presence of gypsum proved to be even more effective and caused the opposite trend (Ca2+ was exchanged for Na+). The cation exchange buffer capacity of carbonates is believed to be particularly effective during dialysis, where the Na+ excess is significantly reduced while carbonate/gypsum dissolution proceeds. The changes of the XRD patterns, particularly the position, shape, and intensity (area) of the basal reflections, could not be attributed to mineral alteration but can be explained by cation exchange, differences of the hydration state, and/or different degrees of preferred orientation, the latter can be explained by particle arrangement. The results of the present study indicate that montmorillonites are stable in NaCl solutions of moderate pH up to 60 °C which is in agreement with most of the available studies. As expected there are no indications for illitization. In addition the study clearly shows the importance of using different chemical, mineralogical, and physical methods in order to unambiguously prove a process as illitization. Literature data indicate that temperatures of >100 °C can lead to irreversible montmorillonite alteration. The same, of course, holds true for extreme pH values, drying, or the presence of K+. These alteration processes have to be considered specifically. [Copyright &y& Elsevier]

Abstract: Cation exchange selectivity for Cs+ and Sr2+ with K-depleted biotite (Na-biotite) and K-depleted muscovite (Na-muscovite) was determined with equilibration for 4 weeks at room temperature. The cation exchange isotherms and Kielland plots indicated that both K-depleted micas show high selectivity for Cs+ at low equivalent fraction of Cs+ on solid. The K-depleted micas took up Cs up to approximately 50% of their theoretical cation exchange capacities. The XRD patterns after Na+ →Cs+ exchange reactions with K-depleted biotite showed that the d(001)-spacings collapsed from ~12.2 to ~11.2 Å with high Cs+ concentrations. This collapse suggests that K-depleted biotite is able to immobilize or fix Cs ions in the interlayers. In case of 2Na+ →Sr2+ exchange, K-depleted biotite showed high selectivity for Sr ions at low equivalent fraction of Sr2+ on solid. The XRD patterns showed that the main d(001)-spacing of the K-depleted biotite slightly increased from 12.16 Å to ~12.3 Å after the exchange reactions with the high Sr2+ concentrations. These results suggest that K-depleted biotite could be used as an ion exchanger to remove radioactive 137Cs as well as 90Sr from groundwater. [Copyright &y& Elsevier]

Abstract: The thermal stability of synthesized and commercial organically modified montmorillonites has been investigated using thermogravimetric analysis (TGA). Four organo-montmorillonites have been prepared by replacing the inorganic cations of a commercial montmorillonite with aliphatic and aromatic ammonium bromide or chloride salts. The modification has been carried out by cation exchange to obtain a high level of intercalation in the montmorillonite. Conformations of the intercalated surfactants have been characterized using Fourier transform infrared spectroscopy (FTIR). Besides fixed organic surfactant, some surfactant in excess still remained in the montmorillonite after repeated washing with water or ethanol/water. The use of a suitable eluent for the surfactants in the washing step was the key issue as shown by the changes of the first degradation peak of Cloisite-Na+-hexadecyl benzyl dimethylammonium (CLO-BDHA), Cloisite-Na+-benzyl triethylammonium (CLO-BTA) and Cloisite-Na+-hexadecyl trimethylammonium (CLO-HTA). Hexadecyl trimethylammonium (HTA) was more sensitive to water and ethanol/water as eluents. Sonication and the use of a polar activator during the modification of montmorillonite increased the amount of surfactant adsorbed by cation exchange. Ammonium acetate method has been revealed as an adequate chemical method to measure the cation exchange capacity (CEC) of inorganic and organic montmorillonites. This method has the advantage with respect to TGA that it does not measure the unfixed surfactant. [Copyright &y& Elsevier]

Abstract: The anionic dye Congo red (CR) was protonated by dissolving it in an aqueous solution of HCl at pH 1.2. Potentiometric titration of CR with HCl, supplemented by previous spectrophotometric studies of CR aqueous solutions at different pH values, revealed that at this pH CR is protonated to a stage that it becomes positively charged (cationic, HCR). The visible spectrum of HCR solution was recorded immediately after its preparation and after different aging periods. Two tautomeric varieties of HCR were identified, ammonium-rich variety, where most amine groups and only part of the azonium groups were protonated and azonium-rich variety, where most azo groups and only part of the amine groups were protonated. The former absorbed at 520 nm and the latter between 600 and 800 nm. The fresh HCR solution showed the predomination of the ammonium-rich variety whereas after one hour aging the azonium-rich variety predominated. The protonated dye (between 7.5 and 75.0 mmol HCR per 100 g clay) was adsorbed by Na-montmorillonite by cation exchange. The visible absorption spectra of aqueous suspensions of HCR–montmorillonite complexes were recorded within two hours after adding the dye to the clay suspensions and after eight weeks of aging. Here also the two tautomeric varieties of HCR were identified. In the fresh suspensions the ammonium-rich variety predominated whereas in the aged suspensions the azonium-rich variety predominated. The transformation of the ammonium-rich variety to the azonium-rich variety is fast in aqueous solutions but is slow in aqueous clay suspensions. After air-drying samples of the HCR–montmorillonite complexes, their visible absorption spectra were recorded. The spectra showed that as a result of drying the azonium-rich variety predominated. The thermal behavior of the solid HCR–montmorillonite complexes was investigated by thermo-visible spectroscopy. By the thermal treatment the dye was deprotonated and converted in part to CR. The deprotonation of the adsorbed dye seems to be a zero order reaction, which does not depend on concentration but on the reaction time. The ratio between protonated azonium and non-protonated CR depended on the loading of the clay. With increasing loadings the azonium variety showed the most intense absorption bands. [Copyright &y& Elsevier]

Abstract: Sorption of metal ions by clay minerals is a complex process involving different mechanisms, and controlled by different variables that can interact. The aim of this work was to study the retention mechanisms of Pb2+ ions on illite. We obtained Pb2+ sorption isotherms at constant pH, sorption edges as a function of pH, sorption isotherms at 5, 25 and 45 °C (pH=5.5), and response surfaces of the simultaneous effect of pH, initial concentration, ionic strength, and temperature on the retention of Pb2+ ions on illite. Surface topography and atomic composition of illite samples doped with Pb2+ were studied by scanning electron microscopy and X-ray fluorescence microanalysis. Below pH 4.5, sorption of Pb2+ ions on illite is via ion exchange with H3O+ and Na+ ions that saturated the exchange sites, where the exchange with Na+ is the main mechanism between pH 3.5 and 4.5. Al3+ ions whose concentration in solution increases with decreasing pH can also compete with Pb2+ ions. For pH above 5.0, proton stoichiometry was higher than 1.0, and the effect of ionic strength on the amount of Pb2+ retained decreased with pH; in fact, at pH 6.8, the amount adsorbed was practically 100% and independent of ionic strength. The pronounced decrease in the intensity of the OH-stretching band for Pb–illite sample at pH 7.0 suggests that Pb2+ ions had lost the inner hydration sphere. The analysis of images obtained by SEM from 3 mM Pb2+ solutions with and without illite showed particles with the same morphology, which indicate a homogenous lead precipitation from the solution. For pH values higher than 4.5, increase in the temperature favored the retention of Pb2+ ions. [Copyright &y& Elsevier]

Abstract: This work deals with cesium diffusion and sorption in rock samples from Bure (Meuse/Haute-Marne, France). Four different samples extracted from the Callovo–Oxfordian layer (between −423 m and −478 m) were investigated to quantify the Cs diffusion parameter range. HTO diffusion properties were also evaluated. The through-diffusion method was used in both cases. The steady-state was reached, allowing a direct access to the values of effective diffusion coefficients (D e). Major attention was paid to experimental chemical conditions. Cs and HTO diffusion parameters were quite homogeneous for the different investigated rock samples. D e(Cs) was found about one order of magnitude higher than D e(HTO). Such observation was already reported in the literature mainly for compacted bentonite. Results presented here show this trend also exists in mudrocks. Batch tests were performed in order to characterize cesium sorption on ground Bure mudrock samples. The isotherms were fitted with a 2-site ion exchange model. This model was extrapolated to intact rock samples and coupled with diffusion equations, using the measured D e(Cs) values. This coupled model was tested against experimental data measured in the transient part of Cs diffusion experiments. A fairly good agreement between model and experimental data was found. [Copyright &y& Elsevier]

Abstract: Ba2+ removal from wastewater by cation exchange using phillipsite-rich tuffs and the subsequent stabilization of the resulting sludge in a cement matrix is reported. Moderate amounts of phillipsite-rich tuff were able to bring, in a short time, the Ba2+ concentration of an experimental wastewater below the legal limits allowed for discharge. Pastes of Portland cement/Ba-loaded tuff were cured for 28 days and characterized from a mechanical and chemical point of view. The compressive strength of the hardened compacts, containing 25–75% of zeolitic material, was much higher than the value of 0.44 MPa, suggested by international protocols for handling and landfilling the solidified wastes. Moreover, experimental leaching of the hardened pastes resulted in a Ba2+ concentration in the leachates much lower than the legal limits allowed for discharge of barium in bodies of water (20 mg/l). [Copyright &y& Elsevier]

Ag+–Na+, Zn2+–Na+, and Cu2+–Na+ equilibria for clinoptilolite-rich mineral from Gördes (Western Anatolia) were investigated at 25 °C and 0.1 N total solution normality. While silver exchange was favorable over the whole concentration range, zinc and copper were partially exchanged and preferred only at low concentrations. The standard free energies of exchanges for Ag+–Na+, Zn2+–Na+, and Cu2+–Na+ pairs were found as -6.0, 2.03, and 3.09 kJ/equiv., respectively. From these values, selectivity sequence was determined as Ag+>Na+>Zn2+>Cu2+. Antibacterial activities of the exchanged samples were measured as a function of exchange level against Pseudomonas aeruginosa and Escherichia coli. Considering the selectivity sequence of the clinoptilolite and antibacterial activity results, Ag-clinoptilolite seemed to be promising antibacterial material. [Copyright &y& Elsevier]

The aim of this study is to examine the effect of various high pH solutions on smectites. The starting materials were a Na,Ca-smectite and two homoionic Na- and Ca-smectites. The experimental solutions were 0.01 m NaOH (pH 12), 1 m K2CO3 and mixtures of 1 or 3 m KCl with 10-4 or 10-2 m KOH (pH 10 or 12). To enhance the reaction rate, all experimental investigations were carried out at 150 °C (±5°C max.), during 2 months. The internal pressure was 5 bars (liquid–vapour equilibrium pressure) when experiments were conducted in warm seal autoclaves and fixed to 150 bars, using standard cold seal vessels. The liquid/clay mass ratio was fixed to 10/1. Integrated data obtained by a multitechnique analytical approach [XRD, electron microprobe, transmission electron microscopy (TEM), scanning electron microscope (SEM) on run products, and inductively coupled plasma atomic emission (ICP-AES) and mass spectrometry (ICP-MS) on experimental solutions] show a distinct behaviour of smectite as a function of experimental fluid composition. In NaOH solution, run products remain low-charge smectites. In KCl+KOH solutions, crystal chemical changes concern mostly the interlayer. A significant replacement of Na by K, and a partial substitution of Ca by K are observed. The tetrahedral Si content does not change, but the total interlayer charge in smectite increases, balancing the changes occurring in the octahedral occupancy (release of Al and Fe). Low-charge smectite transforms into high-charge smectite and byproducts are quartz and feldspars. In the presence of 1 m K2CO3, homoionic Na- and Ca-smectites are unstable and in part replaced by zeolites (merlinoite), feldspars and calcium silicate hydrates (CSH), the latter being dominated by a tobermorite-like phase. The main consequences of the cement or concrete like pore fluid–bentonite contact at elevated temperature induce dissolution of smectite (at various rates), cation exchange and the formation of byproducts (quartz, feldspars, zeolites and CHS). These mineralogical changes affect the expandability and surface area of minerals, and therefore may significantly change the porosity and fluid flow diffusion in clay barriers exposed to high pH fluids. [Copyright &y& Elsevier]

The possibility of solid-state solvent-free modification of Na+-montmorillonite by transition metal salts (NiCl 2 •6H 2 O, CoCl 2, FeCl 3 •6H 2 O) and quaternary ammonium salts (cetyltrimethylammonium bromide, dioctadecyldimethylammonium chloride, alkylbenzyldimethylammonium chloride) was investigated in the presence of water or ethanol. The introduction of water or ethanol was necessary for the effective modification, small amounts (4–8 mmol per 2 g clay) were sufficient, as was the crystallohydrate water in the case of FeCl 3 •6H 2 O. Solid-state intercalation produces metal cation- and organo-modified montmorillonites (M-Mt and O-Mt), which were studied by wide-angle X-ray diffraction (WAXD), wavelength dispersive X-ray fluorescence analysis (WDXRF) and thermal analysis (TGA). On mechanochemical interaction during grinding Na+ and Ca2+ were exchanged for intercalant cations, the residual amount of initial cations in the rinsed modified montmorillonite did not exceed 0.1–0.2%, measured by WDXRF, and NaCl was produced as a distinct WAXD phase in quantities consistent with WDXRF, from 3.0% to a theoretical maximum of 5.6%. M-Mt were identical in structure and composition to ones obtained by solution modification. For O-Mt, the intercalation and modification proceeded to a larger extent compared to solution-modified and commercial equivalents, and with a substantially higher basal spacing (by 2–3 nm) and modifier content. The products were obtained as fine powders that did not require subsequent dispersion and fractional separation. • Metal- and organo-montmorillonites were obtained by solid-state solvent-free method. • Modification was dependent on water or ethanol presence in small amounts. • The formation of NaCl (NaBr) is a direct WAXD proof of clay modification. • Solid-state organomodification proceeds deeper and more effective than from solution. • The products do not require subsequent dispersion, grading or washing. [ABSTRACT FROM AUTHOR]