X-ray diffraction (XRD) profile analysis of eight synthetic hematite samples was performed to identify the best parameters for determining the apparent mean crystallite dimension (D) and, consequently, surface area, The samples are comparable to soil hematite with respect to crystallinity. The procedure included: a) deconvolution of the XRD peaks to Gauss and Cauchy components and subtraction of the instrumental profile, b) determination of D from full-width at half-maximum, integral breadth, and integral breadth measurements of the Cauchy component, and c) comparison of deduced surface areas with those obtained by the N2-BET adsorption method. As expected, D values are strongly influenced by the broadening parameters. An appropriate selection of peaks is required to obtain size values along the crystallographic axes a (hkl: 110,300) and c (hkl: 104, 116) and to calculate reliable surface areas. Using the Cauchy component of the above peaks, the calculated surface areas compared well with those measured by the N2-BET adsorption method.

A synergistic mechanism for the retention of organic and inorganic pollutants in clays is discussed in this paper. The mechanism of adsorption of cis- or trans- 1,2-dichloroethylene vapor (CDE or TDE, respectively) by hydrated smectite clay (hectorite) exchanged with Pb2+, Hg2+, Cd2+, Ca2+, Ag+, or Na+ has been investigated by simultaneously measuring chlorohydrocarbon uptake and water desorption isotherm and by recording the infrared (IR) spectrum of the adsorbed phase. Hydrated hectorite saturated with divalent cations adsorbs about 55% more CDE or 35% more TDE than those saturated with monovalent cations. The quantity of chlorohydrocarbon adsorbed is also a function of the hydration of the clay interlayer space. When dehydrated, hectorite does not adsorb CDE or TDE. Upon long outgassing at room temperature or even at 100°C, the characteristic IR bands of clays with adsorbed chlorohydrocarbon, although much weakened, are still observable. The ratio of the amount of water desorbed to the amount of chlorohydrocarbon adsorbed varied from about 0.22 to 0.34. A shift of the center of gravity of the hydration water OH stretching frequency towards a higher wavenumber and of the asymmetric CC1 stretching vibration toward a lower frequency suggest that the formation of hydrogen bonds between CDE or TDE and water is the driving force for adsorption and that the cation-dipole interaction does not play a major role.

The distribution and chemical state of Si in a synthetic 2-line ferrihydrite with a Si/(Si + Fe) molar ratio of 0.11 was studied. Heat treatment under oxidizing conditions shows that Si-rich ferrihydrite is stable to 400°C. The transformation to hematite and the formation of a polymerized amorphous-silica phase occur at 850°C. At this temperature, the specific surface area decreases greatly and the average pore diameter increases, which is indicative of sintering. Heating under severe reducing conditions causes a segregation of Si from Fe and results in a mixture of elemental Fe and SiO2. Surface and structural data suggest that Si is located near the particle surface where it limits the rearrangement of Fe octahedra to form hematite.

In this study, the effects of two different ammonium-exchange methods to improve the ammonia (NH3) gas adsorption of raw clinoptilolite (CLN) from Gördes (Türkiye) was investigated. The first method involved direct modification of CLN by 0.5 or 1.0 M NH4NO3 solutions at 80°C for 4 and 8 h followed by calcination. In the second method, CLN was converted to the Na+ form prior to modification with ammonium nitrate and calcination under the same conditions. Both methods yielded H+ forms of CLN through the removal of exchangeable cations without damaging the crystal structure. Ammonia adsorption isotherms were determined at 298 K for a total of eight different H+ forms synthetized using both methods. The Na-1.0-8h CLN sample with the highest NH3 adsorption capacity obtained using the second method was selected as the parent CLN. In addition, to determine the effects of doping different cations into the structure on the NH3 adsorption properties of the selected parent CLN sample, cation-exchange processes were carried out using 0.5 and 1.0 M NaNO3, KNO3, Ca(NO3)2 and Mg(NO3)2 solutions at 80°C for 4 h. The raw and modified CLNs were characterized using X-ray diffraction, X-ray fluorescence, scanning electron microscopy and N2 adsorption analyses. Cation-exchanged samples with a wide range of NH3 adsorption capacities (3.61–4.93 mmol g–1) were compared with other zeolites from the literature.

The Clay Minerals Society published a complete characterization scheme for its ‘Source Clays’ but not for its ‘Special Clays’. To address this issue, the specific surface areas (SSAs) of the 16 special clays from The Clay Minerals Society were determined using the Brunauer, Emmett and Teller (BET) method of adsorption of an inert gas. Two BET measurements were performed for each of the 16 special clays, and the average BET SSA of each of the special clays was determined. The BET SSA of cookeite is reported for the first time. In the present study, special clays from The Clay Minerals Society are classified under three groups based on their BET special surface area values as Group-I special clays, with BET values of 0.1–10 m2/g, Group-II special clays, with BET values of 10–100 m2/g, and Group-III special clays, with BET values >100 m2/g. Comparisons which proved interesting were the those involving the mixed-layer clays and the synthetic clays. The systematic approach employed in this paper will allow for better comparisons to be made between different clays and will provide a comprehensive database for future applications of such material (e.g. as catalyst carriers, as adsorbents in waste treatments, etc.).

Specific surface area measurements of The Clay Minerals Society source clays were made by the Brunauer, Emmett and Teller (BET) method of adsorption of nitrogen gas. Two replicate measurements of specific surface area were performed for each source clay. All pair values were within 3%, which is very good agreement for this type of measurement.

Contaminant-transport modeling requires information about the charge of subsurface particle surfaces. Because values are commonly reused many times in a single simulation, small errors can be magnified greatly. Goethite (α-FeOOH) and pyrolusite (β-MnO2) are ubiquitous mineral phases that are especially contaminant reactive. The objective of the present study was to measure and compare the point of zero charge (PZC) using different methods. The pyrolusite PZC was measured with three methods: mass titration (MT) (PZC = 5.9±0.1), powder addition (PA) (PZC = 5.98±0.08), and isoelectric point, IEP (PZC = 4.4±0.1). The IEP measurement was in agreement with literature values. However, MT and PA resulted in a statistically larger PZC than the IEP measurement. The surface area of pyrolusite, 2.2 m2g−1, was too small to permit PZC determination by the potentiometric titration (PT) method. Goethite PZC values were measured using MT (7.5±0.1), PT (7.46±0.09), and PA (7.20±0.08). The present work presents the first reported instance where MT and PA have been applied to measure the point of zero charge of either pyrolusite or goethite. The results illustrate the importance of using multiple, complementary techniques to measure PZC values accurately.

The ability of Na+-, Li+-, K+-, Ca2+- and Mg2+-exchanged sepiolites and acid-activated sepiolites to remove ethylene from storage environments was examined. The sepiolite from Sivrihisar deposit, Turkey, was treated with 1.0 M NaNO3, LiNO3, KNO3, Ca(NO3)2, Mg(NO3)2, HNO3 and H2SO4 solutions at 90°C for 4 h. The mineralogical, chemical and textural properties of the materials were examined using X-ray diffraction, X-ray fluorescence, cation-exchange capacity and nitrogen gas adsorption analyses. The main mineral phase present in the materials was sepiolite, with minor dolomite, and traces of quartz and feldspar minerals and amorphous matter. Adsorption isotherms of ethylene at 273 K were measured on sepiolite samples over a pressure range of 0–100 kPa. As a result of partial blockage of the sepiolite channels, the ethylene adsorption capacity on cation-exchanged sepiolite forms (0.376–0.907 mmol g–1) was less than that of acid-activated sepiolite forms (1.279 and 1.308 mmol g–1). The ethylene adsorption capacities of the sepiolite samples were compared with those of other clay-based materials (0.167–1.817 mmol g–1) reported in previous studies of ethylene removal.

The effects of acid activation on the chemical composition, surface area and pore structure of palygorskite from Xuyi (Jiangsu, P.R. China) were investigated systematically using X-ray fluorescence (XRF) and BET techniques. The palygorskite samples were activated with HCl, H2SO4 and H3PO4 of various concentrations at 80ºC for 4 h. The influences of acid concentration and acid type on the chemical composition, adsorption-desorption isotherms at 77 K, pore-size distribution, surface area and pore volume were studied in detail. The contents of most components of palygorskite decrease with increasing acid concentration except for Si and Ti. HCl shows a greater activation activity and its effect on the dissolution of components of palygorskite is greater than that of H2SO4 and H3PO4. It was found that 3 mol l–1 H3PO4 is a more efficient activator for increasing the number of micropores in palygorskite, whereas 12 mol l–1 HCl is more suitable for use in enhancing the number of meso- and macropores. The acid concentration and acid type have a great influence on the surface area and pore volume. HCl is the most effective at enhancing the external surface area and mesopore volume of palygorskite, whereas, H3PO4 is more suitable for use in improving the micropore surface and volume.

Changes in particle organization and pore-spaces with applied mechanical and hydraulic stresses were followed using TEM, SAXS mercury porosimetry and gas adsorption for two Na-smectites, Laponite and hectorite, with similar structural formulae but different particle sizes. The TEM images show that hectorite has particles larger and more anisotropic than those of Laponite. The particles order perpendicularly to the direction of axial mechanical stress and become disoriented under hydraulic stress. According to the SAXS results, Laponite is composed of 1 – 3 small layers and hectorite of more compact (10 – 80 layers) particles. In Laponite, mechanical stress strongly reduces the amount of macropores but does not affect micropores and mesopores; hydraulic stress increases the macropores. In hectorite, the pore-volume is lower than in Laponite. The different techniques used yield complementary results and show the considerable effect of layer dimension on the behaviour and microtexture parameters of smectite submitted to hydromechanical stresses.

The adsorption of C2H4 and H2 gases by bentonite from the Ünye region, Turkey both as raw (B) and as K+-, Li+-, Ag+- and Mg2+ -exchanged forms, was investigated using automated volumetric equipment and pressures up to 100 kPa at 273 K and 77 K, respectively. X-ray powder diffraction (XRD) and specific surface area measurement (BET) methods were employed to characterize the bentonite samples. The C2H4 and H2 gas adsorption capacities of the original and modified forms were in the ranges 1.817–0.201 mmol g−1 and 0.522–0.388 mmol g−1, respectively. The influence of salt modifications on the gas adsorption properties of bentonite is discussed.