Theoretical Cation Exchange Capacity Research Articles

Mineralogical and Technological Characterization of Zeolites from Basin and Range as Pozzolanic Addition of Cement.

The present paper assesses petrographic, mineralogical, chemical, and technological features of different zeolitic tuff samples from various western USA districts of the Basin and Range Province containing mainly erionite, mordenite, clinoptilolite/heulandite and phillipsite. The aim of this characterization is to evaluate the pozzolanic activity of these samples according to European normative UNI-EN 196/5 (Fratini test) to program a possible use as addition for blended cements. Petrographic and mineralogical results show that the two phillipsite-bearing tuffs have a higher theoretical Cation Exchange Capacity (CEC) than the other samples; technological characterization shows a pozzolanic behavior for all the samples but higher for the tuff samples containing phillipsite, which shows a higher reactivity with CaO. All the samples could be thus advantageously employed for the preparation of blended cements, potentially reducing CO2 emissions by 70–90%.

Adsorption Mechanisms of Psychoactive Drugs onto Montmorillonite

The adsorption of psychoactive drugs (PADs) onto sodium-exchanged montmorillonite (Na—Mt) was investigated under two pH conditions. At pH = 2.5, the adsorption was performed through cation exchange and the three PADs were intercalated within the Na—Mt layers. However, the adsorption capacity was lower than the theoretical cation exchange capacity of Na—Mt due to the impact of the acidic conditions on the adsorbent. At pH = 7.5, only Codeine was protonated and its adsorption through cation exchange resulted in the highest amount adsorbed among the tested PADs. Diazepam was adsorbed through weak electrostatic interactions, whereas Oxazepam appeared to be intercalated within Na—Mt layers despite its neutral charge. Consequently, the variation in pH strongly impacts the affinity of PADs for Na—Mt. These initial results highlight the impact of raw clay on the fate of these contaminants within environmental compartments and could pave the way for a green solution to the removal of PADs from wastewater effluents.

Reactivation of cation exchange properties in black shales

Cation exchange capacity (CEC) is among most important properties of sedimentary rocks, broadly applied in various means of geosciences research and industry. The organic matter (OM) in ancient black shales is thought to be a negligible source of cation exchange capacity (CEC), due to the loss of polar functional groups from extensive diagenetic transformations that occur during burial. OM in modern soils and sediments contains weakly bound hydrogen on carboxyl and phenolic hydroxyl groups, providing negatively charged functional groups that facilitate CEC on the order of hundreds of cmol(+)/kg. Kerogen in ancient sediments may either retain a portion of polar oxygen groups or these functional groups can be (re)gained upon drying, revealing an overlooked source of charge in black shales.Analyzing an extensive series of shales from the Baltic Basin (Poland) and Marcellus Shale (USA) with varying OM content and diagenesis we found that CEC, measured using Hexamminecobalt(III), of heated samples (≥200°C) is up to ten times greater than CEC measured on air-dry samples. Moreover, CEC measured on the heated samples is greater than theoretical CEC estimated from clay minerals composition. The excess CEC correlates with the content of oxygen-rich groups determined with OM pyrolysis and infrared spectroscopy. Carboxyl groups formed in OM due to thermal oxidation at temperatures ranging from 200°C to 310°C, in the presence of oxygen and under vacuum, are responsible for excess CEC. Our results reveal that kerogen in black shales is not chemically inert in the case of cation exchange and the OM can provide a considerable portion of the apparent CEC measured in bulk rock samples.

Production of Ultrapure Bentonite Clays through Centrifugation Techniques

In this study, the production of ultrapure Na-bentonite by centrifuge based techniques for organo and nano composite bentonite industry was investigated. Various parameters including centrifuging time, solids content, and g force were studied to determine the set points (cut size) for theoretical CEC (cation exchange capacity) and recovery limits. The experimental results were modeled using Response Surface Method (RSM) with high responses (regression > 85% and correlation coefficients > 0.85). it is shown that the commercial centrifugation equipment operating with residence time of 10–15 seconds and g values lower than 300 g such as Multi Gravity separator (MGS), Hydrocyclones and Falcon/Knelson concentrators are not suitable for obtaining pure quality Na-bentonite, since the set point size (5-8 µm) is higher than 2 µm which is defined for bentonite of high smectite contents. The RSM models demonstrate that only the kind of separators such as decanter centrifuges with operational g forces higher than 600 may exhibit the closest set point to 2 µm and thus enable the achievement of an ultra pure quality bentonite product. These assumptions obtained from the developed model were confirmed by running tests on Falcon and Mozley hydrocyclone separators.

Hybrid Inorganic−Organic Adsorbents Part 1: Synthesis and Characterization of Mesoporous Zirconium Titanate Frameworks Containing Coordinating Organic Functionalities

A series of functional hybrid inorganic-organic adsorbent materials have been prepared through postsynthetic grafting of mesoporous zirconium titanate xerogel powders using a range of synthesized and commercial mono-, bis-, and tris-phosphonic acids, many of which have never before been investigated for the preparation of hybrid phases. The hybrid materials have been characterized using thermogravimetric analysis, diffuse reflectance infrared (DRIFT) and 31P MAS NMR spectroscopic techniques and their adsorption properties studied using a 153Gd radiotracer. The highest level of surface functionalization (molecules/nm2) was observed for methylphosphonic acid (∼3 molecules/nm2). The level of functionalization decreased with an increase in the number of potential surface coordinating groups of the phosphonic acids. Spectral decomposition of the DRIFT and 31P MAS NMR spectra showed that each of the phosphonic acid molecules coordinated strongly to the metal oxide surface but that for the 1,1-bis-phosphonic acids and tris-phosphonic acids the coordination was highly variable resulting in a proportion of free or loosely coordinated phosphonic acid groups. Functionalization of a porous mixed metal oxide framework with the tris-methylenephosphonic acid (ATMP-ZrTi-0.33) resulted in a hybrid with the highest affinity for 153Gd3+ in nitric acid solutions across a wide range of acid concentrations. The ATMP-ZrTi-0.33 hybrid material extracted 153Gd3+ with a Kd value of 1×10(4) in 0.01 M HNO3 far exceeding that of the other hybrid phases. The unfunctionalized mesoporous mixed metal oxide had negligible affinity for Gd3+ (Kd<100) under identical experimental conditions. It has been shown that the presence of free or loosely coordinated phosphonic acid groups does not necessarily translate to affinity for 153Gd3+. The theoretical cation exchange capacity of the ATMP-ZrTi-0.33 hybrid phase for Gd3+ has been determined to be about 0.005 mmol/g in 0.01 M HNO3. This behavior and that of the other hybrid phases suggests that the surface-bound ATMP ligand functions as a chelating ligand toward 153Gd3+ under these acidic conditions.

Uptake of cadmium, copper, and lead by microporous synthetic Na-birnessite

Removal of cadmium, copper and lead with microporous synthetic Na-birnessite (sodium-birnessite) was investigated by carrying out batch-type sorption experiments with 2 days of equilibration at room temperature. The sorption isotherms indicated that synthetic Na-birnessite showed high affinity for all three heavy metal cations. The Na-birnessite was able to take up Cd, Cu and Pb up to approximately 140, 106 and 60%, respectively of its theoretical cation exchange capacity. The above higher uptakes of Cd and Cu than the theoretical cation exchange capacity of birnessite were probably caused by exchange of not only Cd2+ but also CdCl+ species with Na+ and by exchange of not only Cu2+ but also CuCl+ species with Na+. Some exchange of CdCl+ and CuCl+ species as well as some pH-dependent specific adsorption of the Cd and Cu cations resulted in higher than theoretical uptakes. The XRD patterns after sorption of Cd with Na-birnessite showed an increase in the d(001)-spacing from 7.144 to 7.244 A with high Cd2+ concentration, which indicated that interlayer Na+ ions were replaced by Cd2+ ions. After the sorption reactions with high Cu concentrations, the XRD patterns showed that the main d(001)-spacing of the birnessite slightly increased from 7.144 to ~7.179 A. In the case of Pb sorption, the d(001)-spacing slightly decreased to 7.133 A from 7.144 A of the as synthesized Na-birnessite. These results suggest that removal of heavy metal cations by Na-birnessite is likely due to both ion exchange and chemisorption, the latter due to surface complexation at the edges and outer planar surfaces of Na-birnessite. Based on these results, Na-birnessite is proposed as a potential candidate material to remove heavy metal cations from groundwater as well as industrial wastewater.

Uptake of cesium and strontium cations by potassium-depleted phlogopite

Phlogopite mica was equilibrated with 1.0 N sodium chloride (NaCl)–0.2 N sodium tetraphenylborate (NaTPB)–0.01 M disodium ethylenediaminetetraacetic acid (EDTA) solution at room temperature resulting in an almost complete removal (92%) of the mica's interlayer K. X-ray powder diffraction analysis provides additional evidence that hydrated Na + ions had almost completely replaced the interlayer K +. Following equilibration, the c-axis spacing of the mica increased from 10.0 Å to approximately 12.2 Å. Cesium and Sr ion exchange isotherms indicate that K-depleted phlogopite is highly selective for both elements, the Cs + exchange capacity is 1.26 meq/g or 65% of the theoretical cation exchange capacity and the Sr 2+ exchange capacity is 1.94 meq/g or 100% of the theoretical exchange capacity of the mica. Kielland plots indicated that the mica was selective for Cs + when the equivalent exchange capacity of Cs + in the exchanger phase ( X¯ Cs) was < 0.66 and selective for Sr 2+ when X¯ Sr < 0.41. At equivalent fractions greater than these levels, layer collapse and/or steric effects limit the diffusion of these ions into the interlayers of the mica. Analysis of the Cs + equilibrated mica utilizing XRD indicated that a collapse of the c-axis spacing had occurred. Based on the high selectivity of < 45-μm K-depleted phlogopite for Sr 2+ and Cs +, this material may prove useful as an inorganic ion exchanger for these radioactive isotopes.

Ion exchange properties of natural clinoptilolite: lead–sodium and cadmium–sodium equilibria

Abstract In the present work, ion exchange of lead and cadmium on the sodium form of Western Anatolia clinoptilolite is examined at 25 °C and 0.1 total normality. Its total theoretical cation exchange capacity was 2.3 meq/g. But only the sodium was exchanged during the equilibrium experiments. On this basis, the theoretical exchange capacity is 1.74 meq/g. According to the equilibrium studies, the selectivity sequence can be given as Pb 2+ >Na + >Cd 2+ . The maximum exchange levels expressed as the percentage of the theoretical exchange capacity were 100% for lead and 54% for cadmium. Using the equilibrium data, the thermodynamic analysis of the system was carried out. The solution non-ideality correction factor has almost no effect on the Kielland plot and so on the numerical values of the thermodynamic equilibrium constant. The thermodynamic equilibrium constant ( K a ) and the standard free energy of exchange (Δ G °) were calculated as 16.6 and −3.48 kJ/eq. for lead–sodium system; and 0.16 and +2.27 kJ/eq. for cadmium–sodium system, respectively. Comparing the results of the present work with the data in literature, it can be concluded that the ion exchange capacities and cation selectivities of clinoptilolites with different cationic compositions are different. So, one should carry out cation exchange experiments on representative samples from the deposit before using it as cation exchanger for any practical application.

Methods of Determining Cation Exchange Capacities for Clinoptilolite-Rich Rocks of the Logudoro Region in Northern Sardinia, Italy

AbstractClinoptilolite-rich materials from widespread pyroclastic and epiclastic deposits of northern Sardinia were investigated to assess their cation exchange properties and to find the most reliable experimental method to determine their cation exchange capacity (CEC). The CECs were evaluated using a cross exchange method (CEM) and a batch exchange method (BEM). The CEM resulted in values 30–35% lower than the theoretical or expected CEC calculated from the chemical analyses of the clinoptilolite-rich materials. The BEM resulted in CECs 6–12% lower than the expected CECs. Various parameters, such as the grain-size of powders (&lt;64 µm and 125–250 µm) and replacement cation (Na+, K+, Li+, Cs+, NH4+, Ca2+, Mg2+, Sr2+) were evaluated in order to optimize the cation exchange process, i.e. enhance complete exchange. The particle size did not affect the exchange process appreciably. The type of replacement cation had a substantial effect on the experimental CEC determined by the BEM. The NH4+ and Cs+ replacement solutions resulted in the best experimental CECs ranging between 75% and 94% of the theoretical CEC with NH4+ as the replacement cation and 79% and 88% of the theoretical CEC with Cs+ as the replacement cation. The exchange efficiency was also measured as a function of ammonium concentration in the replacement solution (0.50, 1.00, 2.00 and 3.00 M). Experimental CECs ranged between 94% (0.5 M NH4Cl solution) and 99% (1 M NH4Cl solution) of the theoretical CEC for one epiclastic rock sample and between 79% (3 M NH4Cl solution) and 87% (2 M NH4Cl solution) of the theoretical CEC for one pyroclastic rock sample.

A comparative study on the sorption and desorption of Hg, Th and U on clay

The sorption and desorption of uranium, thorium and mercury on a western Anatolian montmorillonite, obtained from the deposit located in Kula, were studied by application of a batch technique. The clay used is a tertiary clay originally found in a rather large geological formation of west Anatolia. It is nearly pure montmorillonite. Its cation exchange capacity (CEC) determination was performed for ammonium acetate by the Mehlich procedure. The mean CEC was found to be 83 meq/100 g, which, taking into account that CEC determinations were carried out on unfractionated material, is in good agreement with previously reported data. The concentration ranges were between 70–1500 ppm for mercury and 100–2000 ppm for thorium and uranium. The relative importance of test parameters, e.g., pH, clay particle size, groundwater composition, contact time and solid/water ratio, which determine the distribution coefficients was studied. The sorption coefficients varied between 2.7–6.4 ml/g for U, 0.22–1.59 ml/g for Th and 152.4–427.2 ml/g for Hg. The differences of distribution coefficients are discussed. The data could be fitted to Freundlich and Langmuir isotherms. The quantities of the sorbed and desorbed Th were much lower than its theoretical CEC's. This attitude was attributed to the blocking of montmorillonite by cation islands sorbed in the interlayer. Hg is sorbed most strongly. The experimental results indicate that the montmorillonites studied should be effective components of the buffer and backfill material and lead to eventual immobilization of these elements, which are environmentally dangerous.

Powder x-ray diffraction study of a cryptomelane-type manganic acid and its alkali cation exchanged forms

Cryptomelane-type manganic acid (CMA), H2Mn8O16 · 2.4H2O, with a theoretical cation exchange capacity of 2.70 meq/g, was prepared and its cation exchange properties were studied as a function of XM which is defined by the ratio of uptake in meq/g to the theoretical capacity. Plots of the corrected selectivity coefficients log KHM vs the fractional exchange M for alkali metal ions on a 2 × 2 type tunnel-structured manganic acid showed a gradual decrease in small XMM regions and a steep decrease in large XMM) were 0.92 for Li+, 0.74 for Na+ and K+, 0.67 for Rb+, and 0.44 for Cs+. These maximums have been attributed to steric limitation as well as a limit on the expansion of the crystal lattice. Some x-ray diffraction (XRD) data of alkali cation exchanged forms were in good agreement with the XRD data of synthetic alkali CMA phases as given in the cards by the Joint Committee on Powder Diffraction Standards (JCPDS). The lattice parameter a0 has been found to depend on the exchanged amounts and the nature of the cations involved, while the c0 value remained almost the same irrespective of the amount of exchange or the nature of the cations.

Ion exchange behaviour of some amine intercalates of α-Tin(IV) hydrogen phosphate monohydrate

The ion exchange behaviour of some amine intercalation compounds of α-tin (IV) hydrogen phosphate (α-SnP) has been investigated in the presence of transition metal ions. It has been found that the behaviour of these intercalates depends upon whether the guest molecule is a mono- or a poly-aamine. For each of the intercalation samples studied the rate of uptake of the metal ion is rapid ( t 1 2 less than 5 min). When the guest molecule is a water-soluble primary mono-amine the uptake of the metal ion is accompanied by the loss of the amine in the form of a soluble alkylammonium ion. The resultant solid product of this reaction is essentially amorphous due to the delamination of the lamellar α-SnP. The surface areas, however are approximately the same (α-SnP 51.6 m 2 g −1, the delamination product 55.9 m 2 g −1). The retention capacities of the α-SnP/allylamine intercalate for Ni 2+, Co 2+ and Cu 2+ were 6.3, 5.9 and 3.5 meq g −1 respectively. This intercalate appeared to be selective for Cu 2+, especially at low copper concentrations in mixed solutions. Intercalation compounds with poly-amines (e.g. 1,2-diaminoethane) also react rapidly with aqueous transition metal ions but this reaction is not accompanied by a loss of the intercalated amine or by delamination and the characteristic d 002 spacing of the intercalate is retained, and the total amount of metal ions absorbed did not exceed 20% of the theoretical cation exchange capacity (C.E.C.).

Adsorption of uranium and thorium from aqueous solutions by the clay minerals montmorillonite and vermiculite

Abstract The adsorption of uranium and thorium from aqueous solutions by montomorillonite and vermiculite has been studied. The uranium and thorium concentration of the solutions varied between 100 and 2000 ppm. The behaviour of vermiculite as adsorbent of uranyl ions was found to be identical to montmorillonite, whereas the quantity of the adsorbed hydroxy‐Th ions was much lower than its theoretical cation exchange capacity. The later is attributable to a blocking of vermiculite's cation exchange capacity by hydroxy‐Th islands adsorbed in interlayer. The adsorption phenomena studied by these two minerals appear to be of the Langmuir type. Similar studies were also performed using a synthetic ettringite (calcium aluminum sulphate mineral) and a synthetic aluminosilicate zeolite of the faujasite type. The short‐time behaviour of the ettringite and faujasite seems to be very similar to montmorillonite and vermiculite and also obeys to the Langmuir equation. On the other hand ettringite and faujasite were found to be very sensitive and unstable in the acid environment, where uranium and thorium exist as distinguished cationic species, and therefore cannot be used for adsorption studies of this type.

Cation Exchange Capacity and Weathering of Muscovite Macroflakes

AbstractThe cation exchange capacity (CEC) of large (3‐ to 7‐cm2) muscovite macroflakes, determined with 45Ca, was 8.6 × 10‐7 meq/cm2 of geometrical surface, a value greater than the theoretical one of 3.5 × 10‐7 meq/cm2 calculated from the structural formula. The greater than theoretical CEC was attributed to exchange in areas of growth planes made accessible to the solution by (hkO) cleavage and by charged particle tracks. Similar values were obtained for BaEC (9.7 × 10‐7 meq/cm2) and CsEC (8.7 × 10‐7 meq/cm2). The excess of BaCl2, CsCl, or NaCl was not completely removed, whereas excess CaCl2 was removed, by five 100% methanol washings, as indicated by radiochemical measurements. The presence of excess BaCl2 and absence of CaCl2 were confirmed by electron micrographs of platinum‐carbon replicas of the muscovite cleavage surfaces, the former being removed by subsequent water washings. Hydrolysis of exchangeable Na was appreciable during water washings in the NaEC determinations, resulting in a considerably lower measured NaEC (1.1 × 10‐7 meq/cm2), but little hydrolysis of exchangeable Ba or Cs occurred in water washings. Electron micrographs showed that the muscovite (001) cleavage surfaces had been etched during extensive salt treatments and that a weathering product had formed on the surfaces. The latter material was insoluble in water, but was removed by treatment with Na citrate‐NaHCO3, indicating a sesquioxidic composition. The CEC of muscovite flakes was unaffected by the etching and the sesquioxidic weathering product.