Cation Exchange Capacity Measurements Research Articles

First assessment of the pore water composition of Rupel Clay in the Netherlands and the characterisation of its reactive solids

AbstractThe Rupel Clay member in the Netherlands largely corresponds to the Boom Formation in Belgium, and this marine, clay-rich deposit is a potential candidate to host radioactive waste disposal facilities. Prediction of the speciation of radionuclides in Rupel Clay pore water and their retardation by interactions with Rupel Clay components requires knowledge about the composition of Rupel Clay pore water, the inventory of reactive solids and understanding of interactions between Rupel Clay and pore water. Here, we studied Rupel Clay material which was obtained from cores collected in the province of Zeeland, the Netherlands, and from drilling cuttings retrieved from a drilling in the province of Limburg, the Netherlands. Pore water was obtained by mechanical squeezing of Rupel Clay material from Zeeland. Additionally, anaerobic dilution experiments were performed in which the clay material was suspended with demineralised water or a 0.1M NaHCO3solution. Solid-phase characterisation included determination of carbon, nitrogen and sulphur contents, measurement of cation exchange capacity (CEC) and sequential extraction of iron phases.In contrast to the pore water in Belgian Boom Clay, pore water collected from the location in Zeeland has a higher salinity, with chloride concentrations corresponding to 70–96% of those in seawater. The high chloride concentrations most likely result from the intrusion of ions from saline waters above the Rupel Clay in Zeeland. Cation exchange during salinisation might account for the observed deficit of marine cations (Na, K, Mg) and excess of Ca concentrations, in comparison with seawater. The measured CEC values at both locations in the Netherlands vary between 7 and 35 meq(100g)−1and are, for most samples, in the range reported for Boom Clay in Belgium (7–30meq(100g)−1).Pore water and solid-phase composition indicate that Rupel Clay from Zeeland has been affected by oxidation of pyrite or other Fe(II)-containing solids. When coupled to the dissolution of calcium carbonates, oxidation of pyrite can account for the elevated sulphate and calcium concentrations measured in some of the pore waters. The relatively low concentrations of pyrite, organic carbon and calcite in the Rupel Clay in Zeeland, in comparison to Limburg, might be an indicator for an oxidation event. Higher contents of dithionite-extractable Fe in Rupel Clay in Zeeland (0.7–2.6mg Fe / g clay) than in Limburg (0.4–0.5mg Fe / g clay) might also be a consequence of the oxidation of Fe(II) minerals. Oxidation in the past could have accompanied partial erosion of Rupel Clay in Zeeland before deposition of the Breda Formation. However, indications are given that oxidation occurred in some of the pore waters after sampling and that partial oxidation of the cores during storage cannot be excluded. Results from dilution experiments substantiate the influence of equilibration with calcium carbonates on pore water composition. Furthermore, removal of dissolved sulphate upon interaction with Rupel Clay has been observed in some dilution experiments, possibly involving microbial sulphate reduction.

Universal scaling of the formation factor in clays: Example from the Nankai Trough

AbstractElectrical conductivity is a fundamental characteristic describing how strongly a network opposes flow of electrical current. In fully water‐saturated porous media the conductivity, represented by the formation factor, is mainly controlled by porosity, connectivity of the conducting phases, and the tortuosity of electrical current paths. Previous work has shown that universal scaling derived from percolation and effective medium theories accurately describes the relationship between formation factor and porosity when the percolation threshold is taken account, as well as the porosity value at which the scaling switches from percolation theory to effective medium theory. We determined the formation factor in clay‐rich sediments based on cation exchange capacity measurements on samples from five scientific ocean drilling sites in the Nankai Trough. We then compared the results to predictions from universal scaling after determining the volume of clay‐bound water and the percolation threshold. We found that the previously reported universal scaling relations hold in these clay‐rich sediments once the corrections are made for the clay‐bound water and that percolation scaling appears to be valid over the entire range of observed porosities, probably due to relatively broad pore size distributions or low pore system connectivity. Our results show that universal scaling can be applied to describe the porosity dependence of the formation factor in clay‐rich sediments when appropriate corrections are made for the presence of clay‐bound water.

CEC and 7Li MAS NMR Study of Interlayer Li+ in the Montmorillonite—Beidellite Series at Room Temperature and After Heating

AbstractThe objective of the study was to contribute to the understanding of the influence of the structure and the 2:1 layer dimension of smectites on cation exchange capacity (CEC) reduction and the hydration behavior of Li-saturated smectites after heating. Five montmorillonites extracted from bentonites of different provenance were saturated with Li+ and heated to 300°C. Initial montmorillonites and montmorillonites with reduced layer charge (RCM) were characterized by comprehensive mineralogical analysis supplemented by CEC measurements, surface-area measurements by Ar adsorption, and 7Li, 27Al, and 29Si magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The CEC of the initial montmorillonites varied between 89 and 130 cmol(+)/kg while the CEC of the RCM prepared at 300°C varied between 8 and 25 cmol(+)/kg. The lateral dimension of the 2:1 layers varied between 70 and 200 nm. The greatest decrease in CEC was observed for the montmorillonite with the largest diameter of the 2:1 layers and the smallest decrease was observed for the montmorillonite with the smallest diameter of the 2:1 layers. 7Li MAS NMR revealed an axially symmetric chemical environment of the hydrated interlayer Li+ with ηΔ = 0 for the chemical shift anisotropy tensor for unheated montmorillonites with >33% tetrahedral layer charge (ξ). The chemical environment is typical of innersphere hydration complexes of interlayer Li+. An axially non-symmetric chemical environment of the interlayer Li+ with ηCS of close to one was observed for all RCM. While the remaining CEC of RCM prepared at 300°C reflected the variable CEC at the edges, and thus the lateral size or aspect ratio of the 2:1 layers, the hydration complex of interlayer Li+ was strongly determined by the isomorphic substitutions in the dioctahedral 2:1 layers.

Characterization of different types of bentonites and their applications as adsorbents of Co(II) and Ni(II)

In this research, the natural bentonite clays collected from different areas in Iran were utilized as adsorbent to study the removal behavior of different Iranian bentonitic clays vs. Ni(II) and Co(II) from their aqueous solutions. The original bentonite clays were characterized with the help of pH, Swell Index, Sediment Index, granulometric (screen) analysis, cation exchange capacity measurement, powder X-ray diffraction, X-ray fluorescence, scanning electron microscopy with energy dispersive atomic X-ray; Brunauer, Emmett, and Teller surface area measurements; and Barrett, Joyner, and Halenda pore size distribution analysis, Fourier transform infrared spectroscopy. While the thermal stability of the samples was studied using thermo gravimetry (TGA-DSC), adsorption experiments were conducted under some constant solution conditions and the removal of Co2+ and Ni2+ ions from their aqueous solutions was tested on various bentonite types and certain bentonite characteristics including pore size, surface properties, etc. The maximum adsorption of 92% took place on sample A1 in the removal process of Co2+ and Ni2+. The adsorption capacities followed the order of Co2+> Ni2+ in single-component systems for sample A2 and A3. The results showed the prevailing metal removal process was adsorption and cation exchange with the initiation in precipitation.

Estimation of soil cation exchange capacity using Genetic Expression Programming (GEP) and Multivariate Adaptive Regression Splines (MARS)

The soil cation exchange capacity (CEC) is one of the main soil chemical properties, which is required in various fields such as environmental and agricultural engineering as well as soil science. In situ measurement of CEC is time consuming and costly. Hence, numerous studies have used traditional regression-based techniques to estimate CEC from more easily measurable soil parameters (e.g., soil texture, organic matter (OM), and pH). However, these models may not be able to adequately capture the complex and highly nonlinear relationship between CEC and its influential soil variables. In this study, Genetic Expression Programming (GEP) and Multivariate Adaptive Regression Splines (MARS) were employed to estimate CEC from more readily measurable soil physical and chemical variables (e.g., OM, clay, and pH) by developing functional relations. The GEP- and MARS-based functional relations were tested at two field sites in Iran. Results showed that GEP and MARS can provide reliable estimates of CEC. Also, it was found that the MARS model (with root-mean-square-error (RMSE) of 0.318 Cmol+ kg−1 and correlation coefficient (R2) of 0.864) generated slightly better results than the GEP model (with RMSE of 0.270 Cmol+ kg−1 and R2 of 0.807). The performance of GEP and MARS models was compared with two existing approaches, namely artificial neural network (ANN) and multiple linear regression (MLR). The comparison indicated that MARS and GEP outperformed the MLP model, but they did not perform as good as ANN. Finally, a sensitivity analysis was conducted to determine the most and the least influential variables affecting CEC. It was found that OM and pH have the most and least significant effect on CEC, respectively.

Influence of mineralogical and morphological properties on the cation exchange behavior of dioctahedral smectites

Structure and morphology determine the smectites properties. Thereby, edge sites play a key role for the reactivity and colloidal behavior of the smectite. Even so, the edge surface area represents only 1–3% of the total surface area its contribution is up to 10% of the cation exchange capacity (CEC). Na-saturated dioctahedral smectites <0.2 μm were characterized in detail with respect to their structure (layer charge, octahedral cation distribution, iron content, and layer charge distribution within tetrahedral and octahedral sheets). Furthermore, reduced charge montmorillonite (RCM) of these materials were studied. Particle dimension was estimated from argon adsorption, calculation of specific surface area and direct observation of single layers by atomic force microscopy (AFM), which also revealed morphology and particle size distribution of single layer. CEC was measured both for Na-saturated samples and RCM using the Cu-trien method over a pH range of 4–9. The Wyoming smectite with a mean layer diameter of 277 nm and a low layer charge of 0.26 eq/f.u. differs strongly from the others smectites with a mean layer diameter of about 100 nm and layer charges between 0.30 and 0.37 eq/f.u. Furthermore, the layer stacking is much higher for the Wyoming smectite in powder and RCM. Accordingly the edge properties differ between the four smectites. Based on calculation of edge site density and CEC measurements, we showed that the RCM can be used to study the edge site reactivity of the montmorillonites. The increase of CEC above their pHPZC,edge is equal for Na-saturated montmorillonite and RCM. The present study highlights the diversity in structure and morphology and resulting edge properties of four smectites.

Qualitative and quantitative mineralogical composition of the Rupelian Boom Clay in Belgium

AbstractThe Boom Clay Formation of early Oligocene age, which occurs underground in northern Belgium, has been studied intensively for decades as a potential host rock for the disposal of nuclear waste. The goal of the present study is to determine a reference composition for the Boom Clay using both literature methods and methods developed during this work. The study was carried out on 20 samples, representative of the lithological variability of the formation. The bulk-rock composition was obtained by X-ray diffraction using a combined full-pattern summation and singlepeak quantification method. Siliciclastics vary from 27 to 72 wt.%, clay minerals with 25–71 wt.% micas, 0–4 wt.% carbonates, 2–4 wt.% accessory minerals (mainly pyrite and anatase) and 0.5–3.5 wt.% organic matter. This bulk-rock composition was validated independently by majorelement chemical analysis. The detailed composition of the clay-sized fraction was determined by modelling of the oriented X-ray diffraction patterns, using a larger sigma star (σ*) value for discrete smectite than for the other clay minerals. The &lt;2 μm clay mineralogy of the Boom Clay is qualitatively homogeneous; it contains 14–25 wt.% illite, 19–39 wt.% smectite, 19–42 wt.% randomly interstratified illite-smectite with about 65% illite layers, 5–12 wt.% kaolinite, 4–17 wt.% randomly interstratified kaolinite-smectite and 2–7 wt.% chloritic minerals (chlorite, “defective” chlorite and interstratified chlorite-smectite). All modelled clay mineral proportions were verified independently using major-element chemistry and cation exchange capacity measurements. Bulkrock and clay mineral analysis results were combined to obtain the overall detailed quantitative composition of the Boom Clay Formation.

Pitfalls in using the hexaamminecobalt method for cation exchange capacity measurements on clay minerals and clay-rocks: Redox interferences between the cationic dye and the sample.

Using cationic dyes, such as hexaamminecobalt trichloride (CoHex), is a popular method for measuring clay minerals' cation exchange capacity (CEC), because a short single extraction followed by colorimetric measurements is sufficient to accurately measure the CEC. In addition, the analysis of the cations extracted provides additional confirmation of the CEC measurement. These cationic dyes are redox sensitive species and, surprisingly, the existing literature does not contain any information on possible biases to the method in relation to this redox reactivity. This study applies the CoHex method to three kinds of clay and clay mineral samples: (i) oxidized smectites (in their pristine state), (ii) chemically reduced smectites and (iii) clay-rock samples originating from various geological formations and preserved from atmospheric oxidation. Redox reactions occur between the Fe2+ in the clay mineral structures and the Co(III) from the cationic dye, leading to greatly overestimating the CEC values calculated from the colorimetric assays. Reduction of the cationic dyes also leads to a large release of ammonia in solution, originating from the coordination sphere of Co(III) in the CoHex. These redox reactions impede correct determination of the CEC value from the colorimetric method for samples containing clay minerals bearing reactive structural Fe2+. However, the CEC can be correctly determined from the analysis of extracted cations: i) if the soluble salts present in the solid sample can be quantified independently and ii) if the samples are not rich in ammonium.

Assessment of the surface chemistry of wood-derived biochars using wet chemistry, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy

In order to understand the reactivity of biochar in soil, we thoroughly examined the carbonaceous surface of different biochars, paying particular attention to the distribution of oxygen-containing functional groups. Biochar was produced from pine, poplar and willow at two different temperatures (400 and 550°C) and characterised using elemental analysis and wet chemistry (Boehm and potentiometric titrations, cation-exchange capacity (CEC) measurement). In addition, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses were performed on both untreated and acid-washed biochar samples. Qualitative relationships were observed between data generated from the titration methods under investigation and XPS analyses, both describing the general distribution of oxygen-containing surface functional groups. Total acidity of biochar ranged widely, between 32 and 1067 mmol kg–1, and was mostly attributed to the presence of hydroxyl or phenol groups. The number of functional groups containing oxygen decreased with increasing pyrolysis temperature, mainly because of a decrease in the content of phenol groups. A quantitative comparison of titrations and CEC (i.e. biochar’s ion-exchange capacity) measurements was compromised by a masking effect caused by the biochar’s inorganic fraction (&lt;8%). An acid-washing step with nitric acid was shown not to alter the biochar surface systematically. The use of potentiometric titrations with an acid-washing pretreatment proved to be suitable to quantify biochar acidic functional groups, and hence biochar acidity.

Use of Raw and Acid-Treated MnO2 as Catalysts for Oxidation of Dyes in Water: A Case Study with Aqueous Methylene Blue

Catalytic wet oxidation has become one of the best options for mineralization of dyes in water. In this work, mineralization of methylene blue in water was tried by using raw and acid-treated (0.50, 0.75, and 1.00 N H2SO4) MnO2 as oxidation catalysts. Fourier transform infrared, scanning electron microscopy, surface area and cation exchange capacity measurements were used to characterize the catalysts. The acid-treated materials showed large increases in surface area while changes in other surface characteristics were moderate in nature. The oxidative destruction of the dye was possible at near room temperature and the process was optimized with respect to interaction time, dye concentration, catalyst loading, pH of the medium, and temperature. The dye (1.0 mg/L) was oxidized to the extents of 88.5%, 96.5%, 96.8%, and 97.7% with corresponding chemical oxygen demand (COD) reduction of 64.7%, 86.4%, 87.2%, and 88.2% by raw MnO2, 0.50, 0.75, and 1.00 N acid-treated MnO2(catalyst loading 2.5 g/L), respectively. The reduction in COD indicated oxidation of the dye to simpler organic compounds achieving mineralization to a large extent. The oxidation followed first-order kinetics and the catalysts could be used up to six repeated runs without much change in activity. Analysis of the intermediate products of oxidation helped in proposing the potential pathways for oxidative conversion of methylene blue.

Synthesis of Zeolite A from Coal Fly Ash by Alkali Fusion and Hydrothermal

Zeolite A has been synthesized by a modified alkali fusion followed hydrothermal process. Hydrothermal was performed at a temperature of 90 °C for 4 h in a stainless steel reactor. Characterization of the synthesized zeolite was conducted using various techniques, i.e. X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and measurement of cation exchange capacity (CEC). The characterization results showed that zeolite A was selectively obtained by this method. The diffract gram, SEM image, and IR spectra of the synthesized zeolite A showed a similarity with the commercially available zeolit A.

Biochar from woody biomass for removing metal contaminants and carbon sequestration

Biochar generated from pinewood via slow pyrolysis was studied for its viability as a soil amendment as well as for its absorptive capacity for Mg, Ca, Cr, and Pb in solution. Cation exchange capacity (CEC) measurements showed that the biochar sample has a CEC of roughly double that of the reference soil sample. A high CEC value indicates that not only can the biochar sample be used as a carbon sequestration agent, but also as a valuable soil amendment for increasing a soil's natural CEC. Biochar was characterized using elemental analysis, SEM, BET surface area, FTIR, and XRF. These results showed that biochar produced via slow pyrolysis possesses several highly beneficial attributes. The metal adsorption characteristics of biochar were studied in presence of various controlling parameters such as pH, contact time, adsorbent dosage, and interfering species. The results confirmed excellent adsorption capacity values of the biochar for Mg(II), Ca(II), Cr(VI), and Pb(II) by producing 440 (pH 7.0), 120 (pH 7.0), 680 (pH 1.0), and 520 (pH 6.0) μmolg−1, respectively. The potential applications of the biochar for removal of these four metal ions from real water samples were also studied and evaluated.

Effects of ageing on elution behaviour of nitrogenous compounds in disposed wastes from landfill sites

Comparative studies of elution and cation exchange capacity (CEC) tests were applied to aged and fresh municipal and industrial solid wastes to examine the effects of ageing on the long-term elution behaviour of nitrogen on leachate in municipal and industrial solid waste landfill sites. Nitrogen in the leachate gradually eluted as organic nitrogen, but not upon transformation of organic nitrogen to elutable inorganic nitrogen compounds in the solid waste. Ammonium in the solid waste, retained similar to its interaction with clay minerals in soil, elutes when exposed to leachate by being replaced with highly concentrated cations or loses its positive charge in high pH in the leachate, which percolates down from the upper layer of the disposed waste. The quantity of ammonium adsorbed into the aged wastes through CEC measurement process by replacement with ammonium acetate was higher than that onto the fresh wastes. That difference in quantities can serve as an index of the ability of the solid waste to withhold ammonium in the leachate that percolates down the landfill layer. Those results demonstrate that ammonification of organic nitrogen in the waste is not the crucial step of the elution of nitrogenous compounds into leachate.

Pozzolanic consolidation of stabilized soft clays

The presence of soft clays underlying foundations has been responsible for failures in several geotechnical and geo-environmental projects. The three aspects of this study dealing with the stabilization of a soft clay through the addition of cement and lime include: (a) determination of the optimum proportions of both cement and lime needed to obtain a stabilized soil, (b) the phenomenon of pozzolanic consolidation which occurs in the cement–lime stabilized soft clay, and (c) using knowledge of the pre-consolidation stress and compression index of the stabilized soft clay as a practical criterion for determination of the optimum additive percentage in soft clays stabilization. The experimental research program designed to investigate the behavior of the soft clay before and after stabilization involved a series of tests that included sedimentation testing, cation exchange capacity measurement, X-ray diffractometry, unconfined compression and consolidation tests. The results indicate that pozzolanic reaction creates a form of pre-consolidation in the cement–lime stabilized soft clay. The reduction in soil settlement is attributed to the pozzolanic reaction in soil-additive interaction resulting in an increase in pre-consolidation stress of stabilized soil. The test results show that pozzolanic consolidation causes an increase in initial pre-consolidation stress of 70kN/m2 for a soft clay soil to 375kN/m2 for the stabilized soil with 6% lime, and to 385kN/m2 for stabilized soil with 6% cement. The series of XRD experiments conducted are used to study the micro-structural aspects of the stabilized soil. The results show that pozzolanic consolidation not only improves strength behavior of clay soils in general, but also reduces the potential for large settlements of the stabilized soft clays — indicating that there is considerable merit in using the consolidation behavior of the stabilized soft clays as a means for determining the required percentages of additives for cement–lime stabilization of soft clays and soft soils in general.

Effects of Nanoporous Montmorillonite Types on the Separation Process of Chromium(III)

Bentonites contain a large amount of nanoporous and nanostructured montmorillonite, which is the dominant mineral determining the adsorptive properties of bentonites. In this study, the analyses of the characterization of bentonites for adsorption application include cation exchange capacity (CEC) measurements, swell index, dry screen (granulometric) analysis, x-ray diffraction (XRD), BET-BJH surface area and pore size distribution measurements, and scanning electron microscopy (SEM). The adsorption of chromium(III) from a 0.01 N Cr(III) solution using bentonites has been studied. The results showed that BNT3 and BNT2 have high CEC values of 100 and 95 mEq/100 g and swell index values of 30 and 24 mm, respectively. The high amounts of CEC and the swell index with high amount of granulometric (particles finer than 36 µm) values indicate that the amount of clay minerals (motmorillonite) is very high. Successful chromium removal efficiencies changed from 94.5% for BNT4 to 99.4% for BNT3. The maximum Cr(III) removal of adsorbents decreased in the following order: BNT3 > BNT2 > BNT5 > BNT1 > BNT4. The removal of chromium was correlated with the variation of bentonite types. This study aims at investigating the effects of different bentonite types on the removal of Cr(III) from synthetic wastewater using low-cost bentonites.

Effects of Algerian Clays Properties on the Adsorption of Cd (II)

In this work, Cd (II) adsorption from aqueous solutions was studied on three Algerian clays: bentonite, kaolin and clay of Djebal Debbagh. Using batch process, these materials were characterized by different methods infrared spectroscopy, X -ray fluorescence, measure of Cation Exchange Capacity (CEC) and specific area, the Adsorption tests were carried out at room temperature. The uptake of cadmium ions from aqueous solutions to the clays has been studied depending on contact time, temperature, agitation speed and pH, which was regarded as a principal factor in the analysis of the adsorption process. The contact time for the maximum adsorption required is 240m. The kinetics was correlated well with the pseudo second-order model. The results show that the uptake of Cd(II) increases with the pH increasing in the pH range of 2.0–12.0. The increase of the temperature negatively influences the process of the adsorption and shows physisorption phenomenon of cadmium ion on the tested materials. The studies on retention of cadmium ion showed that it is mainly influenced by the physico-chemical properties of used clays. Results show that sorption of cadmium ion was higher by bentonite clay than for other clays. In consequence, the tests allowed us to choose bentonite as the material that presents a capacity raised for the adsorption.

Characterization and Surface Properties of Bentonites in the Separation Process of Iron(III)

Bentonite is an aluminum phyllosilicate, a clay consisting mainly of nanocrystalin particles of montmorillonite adsorbent. In this study, the physiochemical analyses of cation exchange capacity (CEC) measurements, methylene blue index (MBI), and characterization of bentonites for separation applications are examined. Some characterizations of bentonite particles such as surface properties were examined by scanning electron microscopy (SEM), x-ray diffraction (XRD), x-ray fluorescence (XRF), and Barret-Johner-Halenda (BJH) pore size distribution measurements. The adsorption of Fe(III) from a 0.01 N solution using bentonites has also been studied. The result showed that the amount of clay minerals (motmorillonite) is very high in sample A2 (from deposits of Toroud, Semnan Province of Iran). Results also show the MBI and CEC along with montmorillonite content were effective parameters on Fe(III) separation. Iron separation with removal efficiency of 52% for sample A1 (from deposits of Toroud, Semnan Province of Iran) is due to the difference in surface active doners (like O), silica entities with more homogeneous surface negative charge, interaction forces, and CEC.

Strategies for the successful preparation of homoionic smectites

Many chemical, mechanical and thermal properties of smectites depend on the interlayer cations. Therefore, homoionic exchanged smectites are prepared in order to investigate the reaction exchange mechanisms and to improve their behavior as function of the interlayer cation. Presently no general protocol exists and many of the suggested procedures lack proof of achieved exchange. Thus, the aim of the present study was to depict strategies and to determine factors for successful preparation of homoionic smectites. Three natural bentonites and one purified bentonite were saturated by different compensator cations using different (Na+, Li+, K+, Ca2+, Mg2+, Cu2+, or Zn2+) chloride solutions. Concentration of the cations in solution varied between 1 and 20 times of CEC. The exchange was repeated one to three times. Extent of smectite interlayer saturation was studied by measurements of cation exchange capacity (CEC) and subsequent determination of the exchanged interlayer cations.Chemical properties of used solution salts influence pH and the surface properties of the smectites. As a result CEC of the smectites was altered by changing contribution from edge charges. It is established that divalent cation exchange was more successful than monovalent cation exchange (Bergaya et al., 2006). Moreover, fractions of high charged 2:1 layers could also hinder homoionic exchange. Finally, successful cation exchange reaction was strongly influenced by soluble accessory minerals and experimental setup.It was found that there is no simple recipe which is equally applicable for all smectites and bentonites, but there is a general protocol considering the following parameters: mineral composition of the sample, smectite CEC and/or layer charge, chemical and mechanical pretreatment, initial interlayer cations, type and concentration of saturating salt, solid–liquid ratio, reaction time, number of repetitions and washing procedure. Finally, proof of interlayer occupation is mandatory.

Sorption site capacities for Cs on the sedimentary rock in Horonobe area

The sorption behavior of radionuclides depends on the content of minerals in geological media. The sorption of radionuclides on minerals has been interpreted as the uptake on the sorption sites on mineral surfaces. However, conventional investigations such as X-ray diffraction analysis cannot avoid large errors in quantification of minerals. Furthermore, the discrepancies of sorption behavior have been often found even on the same kind of minerals. Therefore, the sorption site capacity cannot be effectively estimated by the quantification of minerals. In this study, the sorption site on sedimentary rock sampled in Horonobe area, where the Horonobe Underground Research Center, JAEA, is located, was estimated from the Cs sorption isotherms obtained by sorption experiments. To deduce the fitting parameters, illite content estimated from the amount of extracted K by alkylammonium treatment and smectite content estimated from the cation exchange capacity measurement were introduced to the fitting procedure. The result shows that the sorption site capacities of smectite and illite in the sedimentary rock in Horonobe area are 1.3–1.7×10−4 and 1.4–4.0×10−5eq/g, respectively.

Mineralogical and physico-chemical characterizations of clay from Keur Saër (Senegal)

AbstractThere is interest in exploiting and developing natural resources, particularly deposits of natural clays. Senegal has several clay mineral deposits for which chemical and mineralogical compositions have been little studied. Some of these natural materials are nowadays used in pottery and ceramics. To extend applications, a better basic knowledge is required and, for this objective, the raw clay and separated &lt;2 μm clay fraction from Keur Saër (Senegal) were subjected to chemical and mineralogical studies. Several techniques including X-ray diffraction (XRD), thermal analysis (TG-DTA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N2 adsorption-desorption isotherms, cation exchange capacity (CEC) measurements and solid state nuclear magnetic resonance (NMR) have been used to characterize the material. It was found that the raw clay and the separated clay fraction consist of a mineral mixture in which kaolinite is the main component. 29Si and 27Al MAS-NMR spectra show the presence of silicon atoms linked to three other silicon atoms via an oxygen atom and six coordinated Al atoms. Significant increases in the specific surface area and cation exchange capacity were observed on purification, reaching a maximum of about 73.2 m2g–1 and 9.5 meq/100 g for the separated fine clay fraction while the values for the raw material were around 28.9 m2g–1 and 7.3 meq/100 g.