Cation Exchange Capacity Methods Research Articles

Potential Errors in Cation Exchange Capacity Measurement in Soils Amended with Rock Dust: Two Case Studies

ABSTRACT The use of rock dust in agriculture has increased worldwide and particularly in Brazil since its regulation by Law 12.890 (2013). However, some inconsistent results in standard chemical analysis of soils amended with rock dust have drawn attention, and among them, cation exchange capacity (CEC). This paper evaluates the increase in sum of bases (SB) and CEC of two soils amended with commercial rock dust (magnesium silicate), measured by four methods: ion exchange resin, potassium chloride (KCl), compulsive exchange and cesium adsorption. The maximum possible increase of SB in the soil was estimated based on the total chemical analysis of the rock dust and compared to the measured CEC results. We concluded the resin method inflated the results, due to the dissolution of rock dust particles by the acid extraction used to recover the adsorbed cations in resin beads. These extra cations caused overestimation of the sum of bases and consequently, of the estimated CEC. Among the methods used, direct CEC methods were more appropriate, as well as the KCl, since it does not employ acid extractions at any step. In addition, calculations based on the total chemical analysis of the rock dust can help to identify some of the cases in which the routine analysis is inflated by the dissolution of rock dust.

The Comparation of Water Saturation Approaches to Reveal a Low Resistivity Reservoir Potential Case in Gumai Formation, South Sumatra Basin

The LRLC reservoir zone has been identified in SN-3 well, at the DAP-1 interval on Gumai Formation. This interval has a low resistivity value from 3-5 ohm.m and the drill stem test (DST) results show oil with gas without water. This study is objected to identify the causes of LRLC reservoir in gumai formation and finding a suitable sw calculation method. Some data such as well logs, reports, cores, and XRD are used to calculate petrophysical parameters such as Vsh, Phie, and Sw, and would be validated by DST data. Water saturation (Sw) calculations from Archie and the CEC method (Waxman Smits, Dual Water, Juhasz) were performed and the results were compared. The results showed that the main cause of the DAP-1 interval LRLC zone was the presence of clay minerals consisting of mixed layers (Illite/smectite). These clay minerals will be associated with high cation exchange capacity (CEC) values, with the value 70 (meq/100g), which can increase conductivity and reduce resistivity values. Based on lumping the more optimistic results of sw calculation from Waxman Smits Sw method (Sw based on CEC method). The DST data on the SN-3 well does not have water test data, so the calculation of the Sw value that is close to the Swirr value is considered the most suitable Sw for the low resistivity reservoir conditions of the Gumai Formation in the study area. The best practice for low resistivity reservoir for suitable petrophysical calculation is necessary to pay attention to the rock lithology conditions, the presence of mineral clay, and determining suitable Sw appropriate to the reservoir conditions

Quantification of the Bentonite Content in Diaphragm Wall Filter Cakes Based on Cation Exchange Capacity

Abstract The formation of filter cakes is caused by filtration on the interface between soil and supporting fluid during the construction of diaphragm walls. The supporting fluid, basically a slurry of water and 4–8 % bentonite, is loaded with minerals from the soil while the trench is excavated. The filter cakes, mixtures of in situ soil and bentonite originating from the supporting fluid, are generally believed to be the weakest and therefore most significant transition zone concerning the shear force transfer from the soil to the concrete wall. Previous research has been devoted to the understanding of the composition and mechanical behavior of filter cakes. In this context, the content of bentonite in the filter cake was identified as the governing parameter. The current paper presents a novel concept to determine the amount of bentonite in the filter cake. Based on an iterative approach, the cation exchange capacity (CEC) of the filter cake, the pure bentonite, and the in situ soil is determined. A linear correlation between CEC and bentonite content in the range between 0 and 100 % could be established based on an extensive laboratory program for numerous soils and types of bentonite. This correlation can be applied to determine the bentonite content for a given filter cake. A comparison of the actual bentonite percentage of artificial sand-bentonite mixtures and the bentonite percentage determined by the CEC method revealed a good agreement (R2 ≥ 0.9825). In addition, filter cakes obtained on construction sites were examined, and a maximum deviation of ±0.84 % bentonite content was measured in duplicate tests.

Comparative study of three methods of determining cation exchange capacity of three major soils in the rainforest region of Southwestern Nigeria

ABSTRACT The cation exchange capacity (CEC) of three benchmark soils in the rain forest region of Southwestern Nigeria, were measured by three standard CEC methods. Results obtained were compared with a view to selecting the best suited CEC method for the soils. The study sites were the Teaching and Research Farm of Obafemi Awolowo University, Ile-Ife, and Itagunmodi settlement. Two representative soil profile pits each were established in soils developed in coarse-grained granite and gneiss, fine-grained biotite gneiss and schist, and the amphibolite. The three methods gave different CEC values in the order of CEC-pH 8.2 > CEC-pH 7 > ECEC. There was a significant correlation between soil organic matter (SOM) and the CEC obtained by each of the three methods (P ≤ 0.05), meanwhile, total clay showed no significant correlation. ECEC provided the best estimate of the CEC for the soils and adequate SOM management is crucial to enhance sustainable productivity of the soils.

Combined influence of organo-modified Indian bentonite nanoclay and fire retardants on thermal and fire behavior of vinylester

This article reports synergetic effect of naturally available Indian bentonite nanoclay and fire retardants on the thermal and fire retardation behavior of vinylester. Indian bentonite nanoclay organically modified with hexadecyltrimethylammonium bromide by cation exchange capacity method, along with aluminum trihydroxide and magnesium hydroxide were dispersed in vinylester and tested. Addition of 30% aluminum trihydroxide and 4 wt% Indian bentonite increased the glass transition temperature of vinylester by 24.4%; decreased thermal degradation by 47%, vertical burning rate by 54% and horizontal burning rate by 72%; and increased limiting oxygen index by 56.6% and microhardness by 49.6%.

Clay mineralogy and rock strength of a mid-German diabase: implications for improved quality control

AbstractBasalts and related magmatic rocks such as diabase are frequently used as raw materials in the building and construction industry as dimension stones or as aggregates, where they may form the sub-bases of roads or railway embankments. A major characteristic controlling the quality of the raw materials is the rock strength, which can be affected by the presence of swellable clay minerals (smectites). Increasing smectite content is generally considered to increasingly affect rock integrity. Industrial practice, in which the smectite content is monitored via cation exchange capacity (CEC) methods, on the other hand, showed that both mechanically stable smectite-rich and unstable smectite-poor materials exist. We therefore studied the CEC–strength relation based on twelve samples from a German diabase quarry.As could be expected, the sample with the highest CEC was the least stable. However, the comparison of the rock strength with the CEC of the other samples was less clear. Comparing the CEC of powders and of the 1–2 mm fraction of the same sample provided additional information. In the case of samples which are relatively stable (in spite of high CEC values), the CEC values of the powders were significantly higher than those of the 1–2 mm fraction. Samples with less rock strength, on the other hand, showed equal CEC values of the powder and the 1–2 mm fraction. This difference may be explained by different accessibilities of the smectites for CEC exchange solutions during typical experiments.In conclusion, the application of the CEC method for quality control considering both powdered and 1–2 mm samples allows a more precise estimation of the rock strength to be made, particularly for the comparison of different materials. Although measurement of two CEC values (after both sieving and grinding) would complicate quality control, the present study indicates that valuable additional information, i.e. semi-quantitative information on the accessibility of smectites, is gained.

Evaluating methods for quantifying cation exchange in mildly calcareous sediments in Northern Alberta

Abstract Cation exchange capacity (CEC) and exchangeable cation composition are important properties in defining water–sediment interactions in contaminant transport scenarios, such as the seepage of process-affected water from oil sands tailings impoundments. At present, detailed characterization of these properties has been overlooked in the surficial Pleistocene sediments of the Athabasca Oil Sands region in Canada. Although a great variety of methods for determining CEC exist and continue to be developed, there is a deficiency in detailed comparisons amongst these methods in the literature, and consequently uncertainty still remains as to which extractants/methods are most suitable for use with sediments containing partially soluble carbonate salts. The present study (1) conducts an up-to-date evaluation of several distinct methods for their suitability in characterizing cation exchange properties in mildly calcareous sediments; using them to (2) evaluate the sorptive capacity and easily displaceable cations of mildly calcareous, surficial sediments near Fort McMurray, Alberta. Four conceptually different CEC methods were chosen: (a) a summation method (Lithium Chloride extractant); (b) a method that displaces an index cation after intermediary washes (Sodium Acetate–Ammonium Acetate); (c) a method using a high affinity cation complex (Silver Thiourea); and (d) a titration method using an organic cationic dye (Methylene Blue). Exchangeable cations were characterized using the Lithium Chloride and Silver Thiourea methods. Analysis suggests that the Methylene Blue test is least impacted by the presence of carbonate mineral phases. Results from field sediments suggest that the exchangeable cations, in decreasing abundance, consist of Ca > Mg > K > NH 4 > Na; while the CEC was found to be 4.7 ± 2.7 meq 100 g −1 in the clay-rich glacial till, 0.7 ± 0.0 meq 100 g −1 in the underlying sand and 4.1 ± 2.3 meq 100 g −1 in the till-sand transition zone.

Interlaboratory CEC and Exchangeable Cation Study of Bentonite Buffer Materials: II. Alternative Methods

AbstractBentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proven to be one of the most sensitive parameters for detecting changes in mineral properties in bentonite-alteration experiments. An interlaboratory study of CECs and exchangeable cations for three reference bentonite buffer materials that were used in the Alternative Buffer Material test (ABM) project in Äspö, Sweden, was conducted to create a suitable database. The present study focused on CEC accuracy and compared CEC methods where care was taken to prevent dissolution of soluble minerals such as calcite and gypsum. The overall quality of the CEC and exchangeable cation values measured using non-Cu-trien CEC methods were good, with CECs of 74–91±0.5–3.3 meq/100 g and exchangeable cation values of 22–61±1.2–3.9 meq/100 g Na+, 7–23±0.8–1.5 meq/100 g Mg2+, and 19–39±0.8–1.6 meq/ 100 g Ca2+. The precision was comparable to the standard Cu-trien method even for exchangeable Ca2+, although the laboratories used different solution/solid ratios and reaction-time parameters for Cu-trien which affect carbonate dissolution. The MX80 and Dep.CAN bentonite exchangeable Ca2+ values were more accurate than standard-Cu-trien values. Using the optimized methods of this study, MX80 and Dep.CAN exchangeable Ca2+ values averaged 20.2±1.6 and 38.8±1.4 meq/100 g which amounts to ~70% of the inflated Cu-trien values. A more complex analysis of the CEC data using different methods, anion analyses, and mineralogical analysis is necessary to obtain plausible and accurate CEC values. Even with a more complicated analytical procedure, the CEC and exchangeable cation values were still not accurate enough because of excess anions. Chloride, sulfate, and dolomite might have increased the exchangeable Na+, Mg2+, and Ca2+ values.

Interlaboratory CEC and Exchangeable Cation Study of Bentonite Buffer Materials: I. Cu(II)-Triethylenetetramine Method

AbstractBentonites are candidate materials for encapsulation of radioactive waste. The cation exchange capacity (CEC) has proved to be one of the most sensitive parameters for detecting changes of mineral properties such as swelling capacity and illitization in alteration experiments. Whether measured differences in CEC values of bentonite buffer samples before and after an experiment are (1) actual differences caused by clay structural changes such as illitization or (2) simply data scatter due to the different methods used by international research teams is an open question. The aim of this study was to measure the CEC of clay samples in five different laboratories using the same method and to evaluate the precision of the values measured. The Cu-trien method and four reference materials of the Alternative Buffer Material (ABM) test project in Äspö, Sweden, were chosen for this interlaboratory study. The precision of the Cu-trien method, which uses visible spectroscopy, was very good with a standard deviation of ±0.7–2.1 meq/100 g for CECs that ranged from 11 to 87 meq/100 g. For the same CEC range, analysis of Cu-trien index cations using inductively coupled plasma (mass spectrometry) and atomic absorption spectroscopy were less precise with a standard deviation of ±2.8–3.9 meq/100 g. Based on the measured precision, greater measured differences in Cu-trien CEC and exchangeable cation values of bentonite buffer samples, before and after an experiment, might be actual differences. Great care must be taken when interpreting measured CEC differences, and analytical characterization of any structural changes may be needed. Compared with results from the ‘International Soil-Analytical Exchange’ (iSE) program for soils, most absolute concentrations were much larger for the clays studied; however, for the two parameters exchangeable Ca2+ and CEC the range was similar to the iSE ring test and, most importantly, the precision was comparable. Future studies should discuss the accuracy of CEC and exchangeable cation values and compare them to alternative CEC methods in which care is taken to prevent dissolution of soluble minerals, such as calcite and gypsum.

Mineralogical and chemical characteristics of the bentonite in the A2 test parcel of the LOT field experiments at Äspö HRL, Sweden

The Long Term Test of Buffer Material (LOT) project at the Äspö Hard Rock Laboratory, Sweden, is a series of medium-scale field experiments focused on validating models and hypotheses concerning long term processes in the bentonite buffer of a repository for high-level radioactive waste. The test parcels emplaced in crystalline bedrock consist of blocks of compacted MX80 bentonite embedding a Cu-tube equipped with a heater to simulate the heat generation from radionuclide decay. The A2 test parcel had been subjected to elevated temperature (up to 130 °C) and hydration by a Na–Ca–Cl type groundwater for almost 6 years when it was retrieved to be analysed. The analyses included determinations of chemical composition, cation exchange capacity (CEC), exchangeable cations and mineralogy. Both the bulk bentonite and dialysed, homo-ionic Na-clay (<2 μm and <0.2 μm fractions) were analysed when relevant. Sulphate was redistributed in the heated part of the buffer under the thermal and hydration gradients that prevailed during the test period. Anhydrite accumulated in the warmer parts, whereas gypsum was dissolved in the peripheral parts of the buffer where water was supplied. Carbonate dissolution increased with temperature in the warmest parts, whereas chloride behaved conservatively in all blocks. Cu was incorporated in the bentonite matrix at the surface of the Cu-tube indicating some corrosion, which may be explained by reactions in an early stage of the test when trapped oxygen existed in the system. Along with the dissolution/precipitation reactions the porewater composition changed, which resulted in replacement of exchangeable sodium by calcium and magnesium in the warmest zone. Also Mg in the clay (<2 μm and <0.2 μm fractions) displays a clear gradient with peak values at the heater. Because several of the alternative sinks for Mg were eliminated in the sample preparation prior to the chemical analysis (purified clay fractions, removal of carbonates, Na-saturation) the smectite is suggested a candidate sink for Mg. Parallel with the increase in Mg, a loss in Si is indicated and CEC tends to increase in the clay that had been heated at 130 °C. A loss in tetrahedral Si that is balanced by Al, and replacement of Al by Mg in the octahedral sheet would imply that the layer charge of the smectite increased, which would be consistent with the higher CEC values of these samples. The changes in CEC are, however, close to the analytical resolution of the CEC method and no effect of the changes in chemical composition can be detected in the XRD-characteristics of the clay. Therefore, supplementary high-resolution analyses are required to verify whether the structure of montmorillonite has altered in the test period.

Layer-Charge Characteristics of Smectite in Thai Vertisols

AbstractThe fertility of soils with respect to K+ and NH4+ is often difficult to measure, but is essential for achieving effective agronomic practices. This problem is especially important in the Vertisols of Thailand. The purpose of the study reported here was to characterize the composition and layer-charge behavior of Thai Vertisols in order to understand better their K+ and NH4+ fertility. Topsoil and subsoil clay of 12 representative highly smectitic Vertisols from Thailand were studied. Interlayer swelling of smectite with alkylammonium cations, cation exchange capacity (CEC), and chemical composition were determined. These data and the re-expansion on glycerol treatment of Li-saturated, heated smectite demonstrated that high-charge, Fe-rich beidellite is the major clay mineral in these soils. The beidellite has a heterogeneous layer-charge distribution as measured by the alkylammonium method, with mean values ranging from 0.43 to 0.62 charges per half unit cell. The layer charge determined by CEC and structural formula methods for some almost pure smectites is smaller (0.32–0.54) and greater (0.46–0.69), respectively, than determined by the alkylammonium method. The structural formulae of beidellite confirm that the layer charge originates mostly in the tetrahedral sheet.

Cation Exchange Reactions of Vermiculite With Cu-Triethylenetetramine as Affected by Mechanical and Chemical Pretreatment

AbstractThe cation exchange capacity (CEC) is a characteristic property of expandable clay minerals, such as smectites and vermiculites. The aim of this work was to examine the cation exchange behavior of vermiculite using the Cu-triethylenetetramine (Cu-trien) CEC method and the influence of mechanical and chemical pretreatment, with the ammonium acetate method serving as a reference. The Cu-trien method makes rapid and direct CEC measurements possible. Three different kinds of mill were used to grind a vermiculite sample from Russia, in order to reduce the particle size to &lt;10 µm. The Netzsch CGS 10 dry mill reduced the particle size more effectively than the other grinding methods. Chemical pretreatments were used to remove carbonates, organic matter, Fe oxides, and divalent exchangeable cations from vermiculite samples prior to CEC measurements. Subsamples of ground and chemically pretreated vermiculite samples were saturated with Na, Li, Mg, Ca, and Cu cations to determine the effect of exchangeable cations on measured CEC values. Chemical pretreatment, monovalent cation pretreatment, and 48 h of shaking time were needed to measure vermiculite CEC values effectively using the Cu-trien method.

Three new, quick CEC methods for determining the amounts of exchangeable calcium cations in calcareous clays

AbstractThe cation exchange capacity (CEC) is one of the most important properties of clays in terms of their performance in both natural and technical processes. For decades, common methods for determining exchangeable cations have failed when calcareous clays or soils were examined, because calcite is at least partly dissolved throughout the exchange experiment which in turn increases measureable Ca2+ concentrations. As a result, exchangeable Ca2+ and the sum of exchangeable cations by far exceed the amount of negative charges. In the past, the silver-thiourea method (AgTU) has been modified to overcome this problem (AgTUcalcite), but is unsatisfactory as the method is laborious. In the present study three new methods based on two alternative metal complexes, cobalt(III) hexamine (CoHex) and copper(II) triethylenetetramine (Cu-trien), are proposed. The optimum solid/liquid ratios of these methods and the optimum complex concentration of Cu-trien are reported, depending on the mineralogical composition of the samples. The key development is that the exchange solutions are saturated with respect to calcite prior to the experiment. Approximately 70–90% of the dissolution of calcite present as an admixture in a clay sample is suppressed in the subsequent cation exchange experiment, but not all. The Ca2+ exchange is not suppressed and there is no evidence for any precipitation of this Ca2+. Three possibilities for how to handle this problem are discussed, one of which is to perform no further correction. The resulting error arises from the remaining calcite solubility of the different solutions after pre-treatment with calcite. This corresponds to errors of 0.2–1.3 (CoHexcalcite)and 0.7–8.4 (Cu-triencalcite) meq/100 gCa2+ for samples with small and large CEC values, respectively. As a consequence of the poor performance of Cu-triencalcite for samples with large CEC, a more concentrated Cu-trien5 × calcite solution was developed which performed much better: 0.1–0.8 meq/100 g(Cu-trien5 × calcite). For Cu-trien5 × calcite and CoHexcalcite at least, the errors are in the range of the non-systematic scattering for exchangeable Ca2+ determination. Therefore, the methods suggested provide ‘operationally correct’ Ca2+ values without additional effort. Moreover, owing to the high selectivity of the index cations applied in the present study, only one exchange step is required, providing a significant advantage over the AgTUcalcite method.

Quantitative Determination of Clinoptilolite in Soils by a Cation-Exchange Capacity Method

AbstractA cation-exchange capacity (CEC) method based on ion-sieving properties was developed for the quantitative determination of clinoptilolite in soils. In this method, both zeolitic and non-zeolitic exchange sites in the soil sample are saturated with Na+. The CEC of the non-zeolitic exchange sites is determined by replacing the Na− in these sites with tert-butylammonium ions. The tert-butylammonium ion cannot be exchanged into the zeolitic exchange sites because it is too large to pass through the channels in the clinoptilolite structure. The sample is next washed with NH4OAc to replace the Na+ in the zeolitic exchange sites. The amount of soil zeolite is then estimated by comparing the CEC of zeolitic exchange sites to the total zeolite CEC (175 meq/100 g for pure clinoptilolite). Prior to the CEC analyses, carbonates and organic matter must be removed to minimize interference with the exchange process. A high correlation (r2 = .96) was observed between the abundance of clinoptilolite estimated using the CEC method and the abundance estimated by semiquantitative X-ray powder diffraction analysis.The CEC procedure was used to quantify clinoptilolite in an Aridic Calciustoll soil from south Texas. About 2–5% clinoptilolite occurs in the A and B horizons, and concentrations progressively increase with soil depth to as much as 20% in the CBk2 horizon.

A New Equilibration Method for Cation‐Exchange Capacity Measurement

AbstractA method is proposed for the measurement of cation‐exchange capacity (CEC) of leached soils carrying both variable and constant negative charges at conditions pertinent to the field. The method consists of equilibrating a soil with 0.01 M SrCl2 (five centrifuge washings), replacing the retained Sr with 0.5 M HCl (one centrifuge washing) and determining the replaced Sr by atomic absorption spectrophotometry. The equilibrium pH is measured with the final 0.01 M SrCl2 washing. If desired, exchangeable bases and Al can be determined by collecting the 0.01 M SrCl2 washings. This method was developed because we found that the Gillman's BaCl2‐MgSO4 CEC method has problems due to specific adsorption of SO2−4. For evaluation, the CEC obtained by the proposed method was compared with the sum of exchangeable bases and Al and with the CEC obtained by other methods including saturation‐equilibration with 1 M SrCl2‐0.01 M SrCl2 and 1 M NH4OAc‐0.05 M NH4OAc (pH 7.0), respectively.

A SINGLE-EXTRACTION METHOD USING SILVER-THIOUREA FOR MEASURING EXCHANGEABLE CATIONS AND EFFECTIVE CEC IN SOILS WITH VARIABLE CHARGES

The use of a single extraction with dilute unbuffered silver-thiourea (AgTU) solution (0.01 M Ag+) for measuring exchangeable cations and the cation exchange capacity (CEC) of soils was compared with the conventional effective CEC method, which used N NH4OAc displacement for exchangeable “bases” (Ca, Mg, K, Na) and N KCI extraction for exchange acidity (Al + H). Fifty-seven selected surface and lower B horizon samples of Alfisols, Ultisols, and Oxisols with low-activity clays derived from a wide range of parent materials were used. The two extraction methods gave essentially the same CEC values for all soils studied (R2 = 0.92). Good agreements were also obtained between the dilute AgTU-extractable bases (Ca, Mg, K, Na) and N NH4OAc-extractable bases. The dilute AgTU extraction gave slightly larger values of exchange acidity (Al + H) than the N KCl extraction for most soils. The single-extraction method using unbuffered Ag-thiourea is suitable for rapid, routine measurements of effective CEC and exchangeable cations for soils dominating in variable-charge colloids.

‘Vermiculite’ Determination on Whole Soils by Cation Exchange Capacity Methods

AbstractThe proposed method is a modification of one by Alexiades and Jackson (1965). Calcium exchange capacity (CaEC) and potassium exchange capacity (KEC) are determined, after removal of organic matter and free iron oxides, by saturating the exchange complex with centrifuge washings of pH 7 acetate solutions of Ca or K, respectively. Excess salt in solutions remaining in contact with the soil after saturation is determined by measuring the weight and concentration of the excess solution. The exchangeable cations and excess salt are then replaced by centrifuge washings with 1 N acetate solutions of Mg (for CaEC) or NH4 (for KEC), after overnight 110°C oven-drying to enhance K fixation for KEC. The replaced cations are determined and CaEC and KEC values are calculated. Per cent ‘vermiculite’ is based on the difference between CaEC and KEC (expressed in m-equiv/100 g) and an assumed ‘vermiculite’ in-terlayer exchange capacity of 154 m-equiv/100 g; percentage Vr = (CaEC-KEC/154) × 100. The ‘vermiculite’ interlayer fraction (VIF) of the CaEC may also be calculated; VIF= CaEC-KEC/CaEC. The measured ‘vermiculite’ is shown in quotation marks since the method is open to criticism regarding exactly what is being measured, the assumptions made, etc. and to emphasize that the determination procedure is an operational one for the characterization of cation exchange complexes.Removal of free iron oxides increased both CaEC and KEC values of several soils but percentage Vr was little affected. The amount of K fixation was affected by the drying treatment employed after K saturation (none vs air-drying vs oven-drying). Thoroughly crushing Montana and African vermiculites dramatically increased their CEC and measured ‘vermiculite’ values, but had little effect with two samples of saprolite from chloritic metabasalt.

The compositional join muscovite˗pyrophyllite at moderate pressures and temperatures

An investigation of compositions between muscovite, KAl₃Si₃O₁₀ (OH)₂ and pyrophyllite Al₂Si₄O₁₀ (OH)₂ was undertaken under hydrothermal conditions of 1, 2 and 3,5 kilobars water pressure and temperatures between 250° C and 440° C. The resulting five silicate phases were identified by X-ray diffraction, electron microscope and cation exchange capacity methods. The study permits the determination of the stability of expandable and mixed-layered phases under various physical and chemical conditions. A brief discussion of possible applications to natural mineral assemblages is made.

Cation‐Exchange Capacity of Plant Lignins and Soil Humic Colloids as Affected by pH and Hydrolysis Error

AbstractThe effect of the pH of the buffered saturating solution on the cation‐exchange capacity (CEC) of several plant lignins and soil humic colloids isolated by NaOH and 1,4‐dioxane was determined for the pH range 2.5 to 8.0. The CEC of lignins ranged from 0 to 38 meq/100 g at pH 2.5 and 33 to 130 meq/100 g at pH 8.0, whereas the CEC of soil humic colloids ranged from 40 to 117 meq/100 g at pH 2.5 and 163 to 367 meq/100 g at pH 8.0. For the same plant or soil material, NaOH‐extracted samples were invariably higher in CEC than were dioxane‐extracted samples. The CEC values of the root lignins were lower than those of the shoot lignins irrespective of extraction method. The extent of hydrolysis error throughout the pH range was measured using two comparable CEC methods in which a water‐wash step was included in one case and omitted in the other. Maximum percentage hydrolysis error occurred at pH 2.5. Dioxane lignins of prairie grass and dioxane extracts of the 0‐ to 12‐inch layer of the virgin and cultivated Prairie soils were found to be more susceptible to hydrolysis errors than their NaOH‐extracted analogs.