Cation Exchange Capacity Measurements Research Articles

Wplyw modyfikacji montmorylonitu na wlasciwosci reologiczne organicznych ukladów powlokotworczych z jego udzialem

Rheological properties of coating systems and possibility of their modifications especially by montmorillonite were characterized (Table 1) on the basis of literature data. In the own research either hydrophilic or hydrophobic modification of purified montmorillonite (MMT-S) was carried out. Hydrophylic modification with sodium salts of carboxymethyl cellulose (CMC) of various substitution degree was done while hydrophobic one carried out with amines of long hydrocarbon chain [1-hexadecylamine (A-1), ethoxylated amines containing radicals of coconut acid (A-2) or thallic one (A-3) (see Table 2)]. Spectroscopic methods, namely FT-IR (Fig. 4, 5, 8 and 9), X-ray diffraction (XRD, Fig. 1,2 and 12) and wide-angle X-ray scattering (WAXS, Fig. 13), were used for characterization of an effectiveness of MMT-S modification. In case of hydrophylic modification the largest changes were observed for the samples modified with CMC characterized with substitution degree equal 0.9 and with 50 wt. % of modifier. For hydrophobic modification with amines the part of modifier at least 1.0 CEC (CEC is a measure of cation exchange capacity) was necessary. Mixed modifier A(1+2) appeared to be the best one. Properly modified montmorillonites show improved swelling ability in aqueous and organic media (Fig. 10). It was found, on the basis of viscosity measurements and rheometric investigations, that montmorillonites could govern the rheological properties of waterborne paints and act as thickeners for solventborne paints.

Oxidation of 4‐nitrophenol in water over Fe(III), Co(II), and Ni(II) impregnated MCM41 catalysts

AbstractBACKGROUND: Nitrophenols are toxic constituents of the effluents of petroleum, textile, dye, iron and steel, foundries, pharmaceutical and electrical manufacturing industries. Aromatic nitro compounds are particularly resistant to normal chemical or biological oxidation making them environmentally persistent. Advanced oxidation using appropriate catalysts mineralize these organics to harmless final products. In this work, MCM41‐based catalysts incorporating Fe(III)‐, Co(II)‐ and Ni(II)‐ cations were used for oxidizing 4‐nitrophenol in water under variable conditions of reaction time, pH, mole ratio of the reactant and the oxidant, catalyst load, feed concentration, and temperature.RESULTS: The catalysts prepared were characterized with X‐ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), cation exchange capacity (CEC) and atomic absorption spectrometry (AAS) measurements. In typical reaction conditions of temperature 353 K, time 300 min, catalyst load 2 g L−1 and 10−3 mol L−1 4‐nitrophenol, the oxidation was 48.7, 52.2 and 55.2% with H2O2 and 42.5, 56.6 and 60.2% without H2O2 for Fe(III)‐, Co(II)‐ and Ni(II)‐MCM41, respectively. Pseudo‐first‐order kinetics with kinetic constant of 2.0 × 10−3 to 5.5 × 10−3 Lg−1 min−1 was proposed along with a possible mechanism. 4‐nitrocatechol, 4‐nitropyrogallol, 1,2,4‐trihydroxybenzene, hydroquinone, acrylic acid, malonic acid, and oxalic acid were identified in the oxidation products.CONCLUSION: Introduction of Fe(III)‐, Co(II)‐ and Ni(II)‐ into MCM‐41 by impregnation produced effective catalysts for wet oxidation of 4‐nitrophenol. The catalysts were able to oxidize 4‐NP even without the presence of an oxidizing agent. The results suggest that the transition metal loaded MCM41 brings about a more effective interaction between 4‐NP molecules and OH radicals. Copyright © 2008 Society of Chemical Industry

Surface area and layer charge of smectite from CEC and EGME/H2O-retention measurements

AbstractThe total specific surface area (TSSA) and smectitic layer charge (Qs) calculated from the structural formulae and unit-cell dimensions of 12 pure smectite samples were used as a reference in the design and evaluation of TSSA and Qs measurement techniques based on cation exchange capacity (CEC), H2O retention at 47% RH, and ethylene glycol monoethyl ether (EGME) retention. A thermogravimetric analysis-mass spectrometry (TGA-MS) technique was used to study the release of H2O from smectite on heating, and to introduce a correction for H2O remaining in the smectite after heating to 110°C, because the sample weight at this temperature has been used routinely as a reference in CEC and EGME sorption measurements. A temperature of 200°C was found to be the optimum reference for such measurements.A good agreement between Qs from the structural formula and from CEC was obtained when this correction was applied. The TSSA of smectite was measured with similar accuracy (mean error of ±5–7%) by three techniques: (1) using mean H2O coverage; (2) using mean EGME coverage; and (3) using a combination of H2O coverage and CEC. A reduction of the mean error from 5–7% to 4% can be obtained by averaging these measurements, and a further reduction to 3% by introducing corrections for the dependence of H2O and EGME coverage on layer charge. The study demonstrates that Ca2+-smectite samples at 47% RH have H2O contents corresponding to 88–107% of the theoretical mass of a monolayer and offers an explanation of this variation.

Measurement of Cation Exchange Capacity of Organic‐Matter Fractions from Soils using a Modified Compulsive Exchange Method

This article describes a modified compulsive exchange method suitable for the determination of cation exchange capacity (CEC) over a pH range on solid, separated organic‐matter fractions. The method is demonstrated to be a reproducible and relatively simple means of measuring CEC on fractions separated by physical means in conjunction with hydrofluoric acid (HF) treatment. By including a modification for measuring the residual magnesium (Mg2+) content by dilution and conductivity, the method is simplified to measure CEC versus pH using a single sample; the only laboratory instruments required are pH and conductivity meters and a balance. The lack of agreement between this method and the silver thiourea (AgTU) method for some fractions at low pH is attributed to the uncontrolled variation in solution ionic strength when acid is introduced to effect solution pH changes in the AgTU method.

Hydrothermal synthesis of beidellites: Characterization and study of the cis- and trans-vacant character

AbstractLow-charge beidellites were synthesized by a hydrothermal treatment applied to an amorphous gel phase in basic solution. The hydrothermal conditions for the syntheses were chosen from the stability field of beidellite previously investigated in the literature. The synthetic samples were characterized chemically and structurally using X-ray diffraction, infrared spectroscopy, cation exchange capacity measurement, and chemical and thermal analyses. We compared the synthetic sample with a natural beidellite sample (SbId) from Idaho, USA, looking at chemical composition and particle size. The main difference is the octahedral site occupancy (cis- or trans-vacant layer structure). The natural SbId sample has trans-vacant layers and the synthetic sample has a preferentially cis-vacant character. This character can be modulated, using specific synthesis conditions. The cis- or trans-vacant layer structure of various synthetic beidellites was investigated at low temperature (<350°C) and pressure (<25 MPa). Depending on the pressure and/or synthesis temperature, the proportion of cis-vacant layers ranges from 20 to 100% and increases with the layer-charge deficit.

Mineralogy, chemistry and physical properties of bentonites from Başören, Kütahya, W Anatolia, Turkey

AbstractThe bentonite deposits in Başören Kütahya, W Anatolia, Turkey were formed by alteration of Pliocene perlite and pyroclastic rocks. Two types of bentonites are distinguished in this area on the basis of their physical properties, chemistry and occurrence. Bentonites were examined to determine their mineralogical, chemical and physical properties. Analytical methods include X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analysis and measurement of cation exchange capacity (CEC), swelling volume, water adsorption, bleaching capacity, and firing shrinkage. Bentonites consist mainly of dioctahedral smectite. They also contain zeolite, opal-CT, cristobalite, quartz, feldspar, dolomite and calcite. The ‘Type 2’ bentonites had greater CEC, swelling volume, water adsorption and bleaching capacity than ‘Type 1’. The variation in the physical properties of the two bentonites is attributed to the differences in the non-clay mineralogy and to the chemical composition and nature of interlayer cation.

Measurement of Cation Exchange Capacity (CEC) of Plant Cell Walls by X-Ray Microanalysis (EDX) in the Transmission Electron Microscope

Cation exchange capacity (CEC) characterizes the number of fixed negative charges of plant cell walls and is an important parameter in studies dealing with the uptake of ions into plant tissues, especially in roots. Conventional methods of CEC determination use bulk tissue, the results are the mean of many cells, and differences in the CEC of different tissue types are masked. Energy-dispersive microanalysis (EDX) in the transmission electron microscope allows CEC determinations on much finer scales. Shoot and fine root tissue of Picea abies was acid washed to remove exchangeable cations. Tissue blocks or semithin tissue sections were loaded with 0.2 mM CaCl2, AlCl3, or Pb(NO3)2 at pH 4.0. The amount of Ca, Al, or Pb adsorbed to the exchange sites of cell walls was determined by EDX. The CEC of cell walls of different tissue types was highly different, ranging in shoot tissues from 0 to 856 mM Ca and 5.8 to 1463 mM Al (block loading) or 4.3 to 1116 mM Ca and 0 to 2830 mM Al (section loading). In root tissue, Pb adsorption to semithin sections yielded CEC values between 29.1 and 954 mM Pb. In most P. abies shoot tissues, the binding capacity was clearly higher for Al than for Ca.

I-B Shaly Sand Model: Application to Hydrocarbon Detection

Abstract Hydrocarbon bearing shaly formations can be detected using cation exchange capacity (CEC) shaly sand models. Most CEC shaly sand models still depend on a laboratory measurement of the CEC value. In addition, these models use one value of formation resistivity factor which is a function of the rocks's cementation exponent. Using one formation resistivity factor in shaly sand reservoirs can result in overestimation of the water saturation, which in turn results in overlooking formations with hydrocarbon potential. This paper introduces a new CEC shaly sand model, Ipek-Bassiouni (I-B), that improves the definition of the formation resistivity factor used in shaly sand formations. This model can also calculate the CEC value directly from the well log data. The Ipek-Bassiouni (I-B) Shaly Sand Model considers that an electric current follows two types of paths in shaly sand. One path represents current flow in free water, and another path represents current flow in bound water. The differentiation between these two paths is accomplished by using two different formation resistivity factors in free water and bound water. The two formation resistivity factors are expressed using two cementation exponents for free water and for bound water. The validity of the model was checked using the cation exchange capacity measured from core samples and drill cuttings. Calculated CEC values display a good agreement with the measured CEC values. The estimated water saturations from the model indicate better hydrocarbon detection in the zone of interest. Introduction Water saturation of hydrocarbon bearing shaly formations can be determined using available CEC shaly sand models. Current CEC models are based on cation exchange capacity and the ionic double layer concept. However, the use of these models is impractical because most of the time CEC data is not usually available to the log analyst, hence; a laboratory measurement of CEC is required. Different laboratory techniques to measure this parameter are found to yield different CEC values for the same core sample. Previous researchers at Louisiana State University (LSU)(1–7) have developed a shaly sand interpretation technique, referred herein as the LSU model, based on log data such as resistivity, spontaneous potential, neutron and density logs. This model is based on the Waxman and Smits(8) concept of supplementing water conductivity with clay counter ions conductivity. It also utilizes the dual water theory(9), which relates each conductivity term to a particular type of water, free and bound, each occupying a specific volume of the total pore space. The main assumption of the LSU model is that the counter ion conductivity is represented by a hypothetical sodium chlorite solution. The LSU model is a practical approach that represents the conductivity behaviour of shaly sand. However, same as all previous models, the LSU model also assumes that the electric current follows the same path in both free and bound water areas. This leads to the use of the same formation resistivity factor to evaluate the shaly formations. This assumption can cause hydrocarbon bearing shaly formations to be overlooked due to overestimation of water saturation in the zone of interest.

Undergraduate Introductory Quantitative Chemistry Laboratory Course: Interdisciplinary Group Projects in Phytoremediation

In this interdisciplinary laboratory course, groups of beginning students complete semester-long projects studying soil chemistry, plant uptake of metals, and environmental analysis while applying their knowledge to the research area of phytoremediation. Phytoremediation is the use of plants capable of accumulating pollutants to reduce levels in contaminated soils or water. In a series of short experiments, students learn methods for sample collection and preparation including collection of an aqueous runoff sample and digestion of soil and plants. Chemical analysis methods presented include the determination of soil pH, potentiometric titration of carbonates, determination of anions by ion chromatography, measurement of cation-exchange capacity of soil using an ammonium ion selective electrode, and trace-metal analysis using ion chromatography or atomic absorption spectrometry. Students begin reviews of scientific literature early in the course that are relevant to their projects, use computer software t...

Ammonium fixation in selected California decomposed granites

Revegetation on disturbed, low organic matter content, decomposed granite (DG) substrates are limited by low plant-available moisture and nitrogen. Data from a single DG site in northern California, USA, showed that a significant fraction of the ammonium from fertilizers or organic matter mineralization was fixed into silicate interlayer positions. To evaluate the broader relevance of NH 4 + fixation, the NH 4 + fixation capacities of 11 other drastically disturbed DG substrates throughout California were evaluated. The fixation capacities of the substrates were quite varied and increased as added NH 4 + application levels increased (124–1,670 kg NH 4 + ha−1). When amended with 124 kg NH 4 + ha−1, 7 of the 11 substrates fixed between 14 and 78% of the added NH 4 + . Analysis of particle size fractions of a typical material indicated that the very fine sand fraction had the highest fixation capacity and the clays and very coarse sands had the lowest, on a gravimetric basis. The overall fixation capacities showed no significant relation to potential predictive characteristics, including extractable K+, NH 4 + , or total N levels. Three methods of cation exchange capacity (CEC) measurement were tested for their ability to predict NH 4 + fixation. The Ba method which utilizes an indicator cation that is not subject to interlayer fixation was not a reliable indicator of NH 4 + fixation. The NH 4 + method had the strongest relation to NH 4 + fixation in the DG materials. The difference between the measured CEC of the NH 4 + method and the Ba method was found to be most predictive of NH 4 + fixation.

Experimental studies of the interactions between anaerobically corroding iron and bentonite

In the horizontal emplacement concept (KBS-3H) for the disposal of radioactive waste, which is being developed in Sweden and Finland, copper canisters will be surrounded by bentonite buffer and placed in perforated steel containers in long horizontal boreholes in the crystalline bedrock, at a depth of ≈500 m. Under the chemical conditions in a deep repository, it is possible that the release of iron from the steel containers could influence the physico-chemical properties of the bentonite, for example, by exchange of the interlayer ions. In order to gain further insights into this process, an experimental study was undertaken, to investigate the mode of iron uptake into bentonite and the extent of changes induced in the basic physico-chemical properties of bentonite. The samples were taken from long-term anaerobic corrosion tests of carbon steel or cast iron in compacted bentonite (Na/Ca-bentonite: Volclay MX-80, ∼4% Fe 2O 3) in contact with a simple artificial groundwater at 30 °C or 50 °C. A range of analytical techniques was applied to samples of corrosion product on carbon steel and cast iron and to the bentonite surrounding the corroding specimens. Corrosion products and bentonite samples were analysed using scanning electron microscopy (SEM), electron microprobe analysis (EPMA), Raman spectroscopy, X-ray diffraction (XRD) and Mössbauer transmission spectroscopy. In addition, the bentonite samples were analysed using Fourier transform infra-red spectroscopy (FTIR), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) and selected area electron diffraction (SAED), exchangeable cation analysis and cation exchange capacity (CEC) measurements. Hydraulic conductivity and swelling pressure were also measured. From visual observation, the corrosion product formed on the carbon steel in bentonite was less voluminous than that formed on steel in artificial porewaters with no bentonite, although previous work showed that the corrosion rates were slightly higher in the presence of bentonite. The Raman spectroscopy analysis showed that corrosion products on the surface of carbon steel and cast iron consisted of an inhomogeneous mixture of magnetite, hematite and goethite. The predominant species was magnetite. In the bentonite, the concentration of iron decreased with increasing distance away from the iron–bentonite interface, with local iron concentrations as high as 20 wt% in some experiments. The total iron content of the bentonite in contact with corroding carbon steel wires increased by several percentage points during the experiments and the cation exchange capacity of the bentonite was reduced. After contact with corroding steel wires the hydraulic conductivity of MX-80 increased substantially. The results of the analyses were consistent with ion exchange of Fe 2+ ions with Na + ions in the montmorillonite interlayer positions but the exact chemical location of all the additional Fe 2+ ions is currently uncertain. There was no evidence for the transformation of montmorillonite to an iron-rich clay mineral phase.

Examination into the Accuracy of Exchangeable Cation Measurement in Saline Soils

Despite the increasing prevalence of salinity worldwide, the measurement of exchangeable cation concentrations in saline soils remains problematic. Two soil types (Mollisol and Vertisol) were equilibrated with a range of sodium adsorption ratio (SAR) solutions at various ionic strengths. The concentrations of exchangeable cations were then determined using several different types of methods, and the measured exchangeable cation concentrations were compared to reference values. At low ionic strength (low salinity), the concentration of exchangeable cations can be accurately estimated from the total soil extractable cations. In saline soils, however, the presence of soluble salts in the soil solution precludes the use of this method. Leaching of the soil with a prewash solution (such as alcohol) was found to effectively remove the soluble salts from the soil, thus allowing the accurate measurement of the effective cation exchange capacity (ECEC). However, the dilution associated with this prewashing increased the exchangeable calcium (Ca) concentrations while simultaneously decreasing exchangeable sodium (Na). In contrast, when calculated as the difference between the total extractable cations and the soil solution cations, good correlations were found between the calculated exchangeable cation concentrations and the reference values for both Na (Mollisol: y=0.873x and Vertisol: y=0.960x) and Ca (Mollisol: y=0.901x and Vertisol: y=1.05x). Therefore, for soils with a soil solution ionic strength greater than 50 mM (electrical conductivity of 4 dS/m) (in which exchangeable cation concentrations are overestimated by the assumption they can be estimated as the total extractable cations), concentrations can be calculated as the difference between total extractable cations and soluble cations.

Treatment of uranium‐contaminated waters using organic‐based permeable reactive barriers

AbstractA literature review and screening study suggest the feasibility of using low‐cost organic materials within a permeable reactive barrier (PRB) to treat ura‐nium‐contaminated water. Natural peat deposits remove and sequester ura‐nium from ground water under certain geochemical conditions while several species of bacteria, including Desulfovibrio desulfuricans precipitate soluble uranium from solution. Cation exchange capacities were measured for saw‐dust and peat, materials to be used in construction of a small‐scale PRB. Re‐sults of a literature review and the cation exchange capacity measurements suggest that organic materials, such as peat, can be used to remove soluble uranium from contaminated water. © 2006 Wiley Periodicals, Inc.

Applicability of the SER method for quality control of clays from the German ‘Westerwald’

The SER method was developed in 1998 for the in situ quality control of Bavarian bentonites. By considering water content and temperature, the cation exchange capacity (CEC) could be calculated from specific electrical resistivity (SER) data, gathered directly in the open pit. The CEC in turn is used for the estimation of the smectite content of bentonites which to a great extent determines the raw material quality. In this study the SER method was applied to clays from the Westerwald (Germany) that are mainly used for the industrial production of ceramics. The aim of this study was to a) assess the applicability of the SER method for fast quality estimation of industrial clays other than bentonites and b) increase the knowledge about electrical conductivity mechanisms of clays. A set of 25 samples from four different pits was gathered and the specific resistivity measured simultaneously. The obtained data were set in connection with laboratory results for cation exchange capacity (CEC) measurements, quantitative chemical and mineralogical composition (XRD, Rietveld analysis) and particle size. The specific electrical resistivity of the ‘Westerwald’ clays is mainly determined by the CEC and the water content at a given temperature. For these clays a similar correlation function as for Bavarian bentonites was obtained. Therefore, the specific electrical resistivity of ‘Westerwald’ clays is strongly influenced by the presence of smectitic layers (smectite and smectitic layers in illite/smectite mixed layer minerals) since smectitic layers significantly determine the CEC even in the presence of other clay minerals like kaolinite or illite. In conclusion, smectitic layer and the water content determine the electrical properties of the investigated clays containing only 10–20% w/w smectitic layers. The SER method is applicable for the in situ estimation of the CEC of Westerwald clays being relevant for their industrial application.

Lead recovery from PbZrO 3 using wet ball-mill technique and hydrothermal synthesis of α-zirconium phosphate from wastewater for resource recovery

Lead recovery from lead zirconate (PbZrO 3) ceramics was investigated using a wet ball-mill treatment in H 2SO 4 aqueous solution. Subsequently crystalline α-zirconium phosphate (α-Zr(HPO 4) 2·H 2O) was synthesized using a hydrothermal technique in order for the resource recovery of zirconium in the wastewater after the wet ball-mill treatment. A wet ball-mill treatment in 4.5 M H 2SO 4 aqueous solution for 24 h was capable of converting more than 99.9% of the Pb initially included in the PbZrO 3 to solid state PbSO 4 with a purity of 98%. On the other hand, the Zr in the PbZrO 3 was dissolved into the acidic solution during the treatment. The Pb and Zr metal elements coexisting in PbZrO 3 were successfully separated by the wet ball-mill technique. Then, resource recovery of zirconium in the wastewater was examined. Crystalline α-Zr(HPO 4) 2·H 2O was synthesized by hydrothermal treatments in 3.1–12.5 M H 3PO 4 aqueous solutions at temperatures of 120–240 °C for a duration of 70 h. The hydrothermally prepared powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and then they were also evaluated in terms of cation exchange capacity (CEC) measurement and thermogravimetric (TG) analysis.

Correlation between surface properties and catalytic activity of clay catalysts

Surface properties always have a strong bearing on catalytic activity. Modification using mineral acids results in the variation of properties like acidity, cation exchange capacity, surface area and porosity of a clay mineral. The present investigation involves the preparation, chemical characterization and surface property evaluation of a set of catalysts, prepared by the acid activation of bentonitic clay collected from Kutch district of Gujarat, India. Chemical characterization was carried out by conventional chemical analysis, physical characterization by XRD, FTIR and DTA and surface property evaluation by surface area, acidity and cation exchange capacity measurements. Activity of the catalysts was monitored by the test reaction, benzylation of benzene. It was found that there is very good correlation among catalytic activity, acidity and cation exchange capacity. The catalyst having the maximum cation exchange capacity showed the maximum conversion in the test reaction. Correlation between iron content and catalyst performance has also been examined. The results obtained in the benzylation of substituted benzenes and polycyclic hydrocarbons are presented. The performance of the catalysts has been compared with the commercial catalysts, K 10 and KSF/0.

Influence of dispersion conditions of two pharmaceutical grade clays on their interaction with some tetracyclines

This paper examines the influence of dispersion conditions of two pharmaceutical-grade clay minerals on their interaction with some Tetracyclines. Both the mineralogical and chemical compositions of the clay samples were determined and their structural formulae calculated. Cation exchange capacity (CEC) measurements were also performed on mineral samples, and subsequently, absorption studies were done according to a screening factorial design, by dispersing a known amount of clay in a solution containing a known drug concentration under different conditions (i.e. mixing rate and equilibrium time). The clay samples differed in their mineralogical and chemical compositions, and so must be considered different pharmaceutical materials (“Purified Bentonite” and “Magnesium Aluminum Silicate”). Cation exchange capacities were similar, but different individual amounts of each exchangeable ion as well as amounts of drug retained were detected. Moreover, dispersion conditions greatly affected drug absorption for both minerals. Higher retained amounts were achieved at low equilibrium time when a high mixing rate was applied to broken down clay aggregates. Similar responses were also obtained with low mixing rate as long as a high equilibrium time was used. Therefore, if what is sought is maximum sorption capacity, optimization of dispersion conditions must be achieved before considering any batch test. In particular, high mixing or prolonged equilibrium times increased the amount of drug retained onto the studied clay samples.

Use of Diffusion to Determine Soil Cation-Exchange Capacity by Ammonium Saturation

Soil cation-exchange capacity (CEC) is often determined by NH4 saturation, using a 1 M solution of NH4C2H3O2 at pH 7. A study was conducted to ascertain whether this determination can be performed by employing a simple diffusion technique previously developed for direct inorganic-N analysis of soils. Values obtained for 10 diverse Illinois surface soils following overnight NH4 saturation were correlated very highly with CEC data collected for the same samples on the basis of NH4 analyses by steam distillation (r = 0.999, P < 0.001) or colorimetry (r = 0.999, P < 0.001), and also with data obtained by summing atomic absorption measurements of calcium (Ca), magnesium (Mg), and potassium (K) displaced during NH4 saturation (r = 0.811, P < 0.01). As a much more rapid and convenient alternative to existing methods for preparation of NH4-saturated soil, a simple saturation technique was developed whereby 0.500 g of soil was leached under vacuum with 15 mL of 1 M NH4C2H3O2 (pH 7) in a 10-mL disposable syringe containing a stainless-steel frit, and then with 30 mL of 2-propanol. After drying for a few minutes, the soil sample was transferred to a 473-mL (1-pint) wide-mouth Mason jar, treated with 10 mL of 2 M KCl, and analyzed for exchangeable NH4 by diffusion with MgO for 1.75 h at 45–50°C on a hot plate. Except for a calcareous soil, CEC measurements by the rapid saturation-diffusion approach did not differ significantly (P < 0.05) from diffusion data involving overnight NH4 saturation. This approach allows CEC determinations to be accomplished in a few hours instead of days, and will be especially useful for routine soil characterization and testing.

Alteration of the Callovo–Oxfordian clay from Meuse-Haute Marne underground laboratory (France) by alkaline solution. I. A XRD and CEC study

The reaction of the clay fraction of the Callovo–Oxfordian hard shale formation hosting the French underground laboratory site, with high pH NaOH, KOH and Ca(OH) 2 solutions has been investigated through closed system experiments at 60, 90 and 120 °C over 6, 24 and 168 h. The mineralogical composition of the run samples has been determined using X-ray diffraction (XRD) of randomly oriented powders showing the formation of different species of zeolites (analcime, chabazite, phillipsite) and Ca silicates (tobermorite, katoite). The phyllosilicates were studied using XRD of oriented preparations and cation exchange capacity measurements. Detrital or diagenetic mica and chlorite in the <2 μm fraction remain unchanged. On the contrary, the smectite and random illite–smectite mixed layer minerals are strongly reactive. The expandable layers of montmorillonite type are selectively dissolved while beidellitic ones survive or are transitionally formed.

A New Method for the Simultaneous Measurement of pH‐Dependent Cation Exchange Capacity and pH Buffering Capacity

The pH dependent cation exchange capacity (CEC) and pH buffering capacity (pH BC) are two crucial properties in soil fertility management of variable charge soils. However, they are rarely measured, since most of the existing methods are cumbersome and time‐consuming. We propose a new method, based on the silver‐thiourea (AgTU) method, for the simultaneous measurement of pH dependent CEC and the pH BC. In general, this method consists of first increasing the pH of the soil to about pH 7 and then gradually acidifying the soil by titrating with HNO3, while measuring pH and CEC after each equilibration. This way, both CEC at different pH values and the pH BC are measured on the same sample, without the multiple washing steps needed in other procedures. Various aspects of the proposed method were tested and the results obtained were compared with the ion adsorption method. The modified AgTU method obtains field relevant results and is suitable for the routine analysis of large numbers of samples.