Smectite Group Clays Research Articles

EXAFS Determination of Clay Minerals in Martian Meteorite Allan Hills 84001 and Its Implication for the Noachian Aqueous Environment

The aqueous environment of ancient Mars is of significant interest because of evidence suggesting the presence of a large body of liquid water on the surface at ~4 Ga, which differs significantly from the modern dry and oxic Martian environment. In this study, we examined the Fe-bearing minerals in the 4 Ga Martian meteorite, Alan Hills (ALH) 84001, to reveal the ancient aqueous environment present during the formation of this meteorite. Extended X-ray absorption fine structure (EXAFS) analysis was conducted to determine the Fe species in ALH carbonate and silica glass with a high spatial resolution (~1–2 μm). The μ-EXAFS analysis of ALH carbonate showed that the Fe species in the carbonate were dominated by a magnesite-siderite solid solution. Our analysis suggests the presence of smectite group clay in the carbonate, which is consistent with the results of previous thermochemical modeling. We also found serpentine in the silica glass, indicating the decrease of water after the formation of carbonate, at least locally. The possible allochthonous origin of the hematite in the carbonate suggests a patchy redox environment on the ancient Martian surface.

Cell viability and bacterial reduction activity of Ag-modified bentonite

Abstract The interest on the potential biomedical applications of clay materials are recently growing. Among the clay minerals, it was found that the smectite group clays are the most suitable for adsorption processes. This group includes bentonite in which the structure is composed of octahedral and tetrahedral layers of silica. In this study, bentonite clays from SAILE Industries, Inc. in Mangatarem, Pangasinan, Philippines were characterized and fabricated as Ag-bentonite composites to determine the potential of the mineral for biomedical applications. Bentonite clay powder was mixed with silver nitrate solution via ion-exchange process. The synthesized powders were filtered using centrifugation and washed with deionized water to remove any excess silver ions. Drying followed at 60°C and stored in a dark container prior to characterization. XRD and XRF was used to evaluate the phase composition and chemical analysis of the Ag-bentonite composite, respectively. The biological tests were also done to investigate the antibacterial and cell viability of the sample.XRD result showed that the sample is composed of the montmorrilonite, hectorite and mordenite phases. Chemical analysis revealed the presence of Ag in the bentonite structure with a content of about 14.24±0.13%. Antibacterial activity of the sample was evaluated using plate reduction method where about 99% reduction of S. Aureus was observed after 24 h. Moreover, approximately 89±4.37% live cells was detected after the 24-h incubation of the sample using lymphocyte culture. With these results, the synthesized AgB samples may find suitable future biomedical use due to its stable structure, antibacterial and biocompatibility properties

Geo-Engineering Properties and Swelling Potential of Quaternary Lacustrine Clays in North of Burdur, Turkey

In areas surrounding the city of Burdur, Turkey, where water contents are high, no swelling–shrinkage-dependent deformations are visible because the active zone depth is adjacent to the surface. There are some deformations in areas with low water levels, especially those with low-rise construction. Thus, in some areas around Lake Burdur, increased swelling–shrinkage-dependent deformation is inevitable owing to a steadily decreasing water level of the lake. However, development around Lake Burdur, such as an organized industrial area, a civilian airport, and a military airport currently under construction, exacerbates the problem. Therefore, we examined swelling potentials of lacustrine clay in the active zone within a selected area around lake. Lacustrine soils in the selected area were studied using a hand auger, with a total of 379 samples at 50 points, through depths of 1–3 m. Clayey levels in the research area were separated into three different clay–clayey levels and were analyzed by X-ray diffraction and scanning electron microscope. Results showed that clay minerals at all levels averaged 39–52 % and that most were smectite group clays. Microstructures were plate-like and were aligned face to face. It was also determined that swelling potentials of all examined clayey levels were high to low, with change between 0.22 and 2.59 % and swelling pressures between 2.9 and 71 kPa. Because the water level was close to the surface, so was the active zone; therefore, deformation was noticeable. Swelling–shrinkage-dependent deformations are inevitable in the future with decreasing lake water level.

NATURALLY OCCURING CLAY, MONTMORILLONITE, AS A DRUG DELIVERY VEHICLE FOR IN VITRO EXTENDED RELEASE OF VENLAFAXINE HYDOCHLORIDE

Normal 0 In the present work, a naturally occurring smectite group clay mineral, Montmorillonite, (Mt) has been explored as a vehicle for delivery of an antidepressant drug Venlafaxine hydrochloride, VF. The effect of pH of the drug solution, time and initial drug concentration on drug loading capacity of Mt has been studied. The adsorption isotherm was fitted by the Langmuir model and follows the pseudo-second-order kinetics. The synthesized Mt-VF complexes were characterized by XRD, FTIR, TGA, DSC etc. VF was found to be intercalated in the Mt layers. The release profile of the VF and Mt-VF complex in simulated gastric and intestinal fluids has been discussed. The release behaviour of VF from Mt-VF complexes appears to be sustained/ extended for a period of 12 h and reaches upto 52% in simulated gastric fluid and is stable in intestinal fluid where as pure VF completely gets released in 5.5 h and 3.5 h in simulated gastric and intestinal fluid respectively Out of all kinetic models used to elucidate the drug release mechanism, the best fitting was observed for first order model. On the basis of present studies it can be stated that the synthesized Mt-VF complexes have the potential for developing in to a sustained release formulation for oral drug delivery of an anti-depressant drug VF. This shows a path which can reduce doses substantially from 4 times in 24h to twice in 24 h.

Effects of Salinization Pathways upon Morphogenic and Geochemical Features of Coastal-Margin Vertisols, Aransas National Wildlife Refuge, Aransas County, Texas

Coastal regions are predicted to experience changes in hydrology in response to climate-induced increases in sea-surface temperatures, sea-level rise, and shifts in weather patterns. These changes will likely alter pathways that marine salts enter coastal soils. This study aims to identify and quantify physical and geochemical changes in salt-affected vertisols and vertic intergrades forming on the Texas Gulf Coast. The characteristic morphogenic features of vertisols are formed as expandable clays experience seasonal fluctuations in moisture content within the profile, and smectite-group clays are more salt-sensitive than other clay types. This, coupled with their prevalence in low-lying coastal regions, makes the vertisol soil order useful for exploring how active pedogenic processes may respond to future climate scenarios. Soils were described and sampled along two transects in the Tatton Unit of Aransas National Wildlife Refuge from the coast of St. Charles Bay inland, including environments ranging from saline coastal prairie to saline-to-brackish tidal flats and tidal marshes. Macro- and micromorphological pedogenic features and geochemical patterns of major cations observed along each transect allowed for the interpretation of the relative influence of salinization pathways at the reserve based on distance from the coast and landscape position. Evidence of salinization due to underlying brackish groundwater was observed along both transects. In contrast, salinization due to surface inputs from marine sediment, tidal influence, and storm surge was more prevalent within the floodplain and at most coastal upland sites. Along both transects, slickensides and desiccation cracks appeared to be limited to the most well-drained upland sites, suggesting that a combination of increased saturation and salinization may be suppressing the formation of macroscopic vertic features.

Swelling problems and triaxial swelling behavior of claystone: A case study in Tire, Turkey

Increase in the volume of rocks containing swelling minerals like montmorillonite and anhydrite due to physico-chemical reaction with water is defined as swelling. If increase in the volume is prevented, a swelling problem which harms engineering structures occurs. In the design of these structures the data obtained from swelling tests should be used. Triaxial swelling test is important in terms of the success of the design. In this study swelling problem caused by claystone containing smectite group clay mineral in Tire Lignite Enterprise (Izmir, Turkey) was investigated and triaxial swelling behavior of the claystone was determined. Key words: Swelling, triaxial, stress, strain, claystone, smectite.

Synthesis and properties of new fluoroelastomer nanocomposites from tailored anionic layered magnesium silicates (hectorite)

AbstractIn the field of polymer clay nanocomposites, naturally occurring smectite group of clays are the most commonly used nanofillers. In the present work, smectite group clay, hectorite was synthesized in the laboratory with an intention to understand the structure–property relationship of polymer nanocomposites, with special reference to the characteristics of the nanoclays. The nanocomposites were prepared using these synthetic clays and fluoroelastomer by a solution mixing process. The clays and their nanocomposites were characterized by using X‐ray diffraction, X‐ray fluorescence, infra‐red spectroscopy, and transmission electron microscopy. It was observed that clay formation was a function of the concentration of the constituent materials. The gallery spacings and surface areas of synthetic clays are higher than those of the natural clay. Mechanical, dynamic mechanical, swelling, and thermal properties of these nanocomposites were also studied. The properties of these nanocomposites were compared with the nanocomposites obtained from natural clays, available commercially. Synthetic clay filled samples showed better properties than the natural clay filled samples, e.g., synthetic hectorite filled sample exhibited 75% increment in tensile strength and 24% improvement in 100% modulus compared with the natural hectorite based system. The results were explained with the help of thermodynamics and morphology. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Application of LAICPMS to trouble shooting mineral processing problems at the Getchell mine, Nevada

A study has been conducted on Au-bearing complex sulfide ore feed and autoclave tailings from the Getchell mine, Nevada. In this study products at different stages of an autoclave process were studied and identification of the source of low recovery in some Au-bearing sulfide ores located. All samples were studied to assess the occurrence of gold and to identify poor performance ores under the standard operating conditions of the autoclave mill. The results show that in the high recovery samples, gold occurs predominately as chemically included atoms within arsenian pyrite. This pyrite is exposed on crushing and oxidises almost completely within the autoclave. Typically recoveries are above 90% for such ore. Where poor recovery is observed, two modes of occurrence are observed in the feed that may prevent complete oxidation of the arsenian pyrite: • Arsenian pyrite occurs as fine inclusions (<40 μm in size) within quartz and illite, even with fine grinding it appears from residues. Such pyrite is not exposed and thus does not get oxidised. • Trace amounts of gold observed by LAICPMS with a mixed illite/smectite clay, montmorillionite and free carbon indicating potential for preg-robbing by clays (particularly the High exchange capacity smectite group clays) and carbon. To overcome these problems, the options include: • Fine grinding would release the gold-bearing pyrite. • Addition of an oxidant such as MnO may remove carbon; or • Surface suppressant to depress surface cation exchange capacity on clays and carbon may remove problems of “preg-robbing”. The test sample in which MnO was added showed an improvement of >13% in gold recovery from a carbon-rich sample.

Geologic setting and characterization of coals and the modes of occurrence of selected elements from the Franklin coal zone, Puget Group, John Henry No. 1 mine, King County, Washington, USA

Upper middle and upper Eocene coal-bearing strata in the Green River coal district of Washington state are in the Franklin coal zone of the undivided Puget Group. Coal-bearing strata accumulated in intertidal and deltaic environments along a tidally influenced delta plain. Numerous shale and tonstein partings within the coals indicate that the coal formed in low-lying peat mires. To evaluate variations in element distribution within these coals, vertical bench channel samples from the Franklin No. 7–8–9 ( n = 24) and the No. 10 ( n = 11) coal beds were collected. Coal beds in the John Henry No. 1 mine of the Green River coal district have an apparent rank of high volatile B bituminous. No. 7–8–9 and No. 10 have a mean sulfur content of 0.67 wt.% and 0.9 wt.% respectively. When compared statistically to other western U.S. Tertiary coals, the Franklin coal zone in the John Henry No. 1 mine Franklin coal zone is significantly higher in contents of ash, Si, Al, Mg, K, Ti, Ag, As, Cu, F, Ga, Hg, Li, Nb, Ni, P, Sc, Sr, V, Y, Yb, and Zr, and has significantly lower contents of Ca, Na, B, Nd, and Se. Mean contents of several elements in the Franklin No. 7–8–9 and No. 10 coal beds are uncommonly high compared to western U.S. Tertiary coals. The No. 7–8–9 bed is higher in As (6.6 X, 44 ppm), Cu (3.8 X, 42 ppm), F (3 X, 190 ppm), Hg (44 X, 4.4 ppm), Mn (3.4 X, 170 ppm), Nb (4.4 X, 10 ppm), Ni (3.5 X, 16 ppm), V (4 X, 68 ppm), and Zr (4.9 X, 88 ppm). The No. 10 bed is higher in As (11 X, 81 ppm), Cu (3.2 X, 35 ppm), Hg (75 X, 7.5 ppm), Ni (3.3 X, 15 ppm), P (5.4 X, 1300 ppm), Sc (4.1 X, 8 ppm), Sr (2.5 X, 680 ppm), V (3.7 X, 63 ppm), and Zr (2.7 X, 48 ppm). X-ray diffraction analysis of the low-temperature ash from these coals reveals the predominance of quartz and clays (kaolinite, minor illite, smectite group, and mixed layer) and minor plagiociase feldspar (albite, disordered, and ordered Ca-bearing), carbonate (ankerite, calcite, kutnohorite, and siderite), pyrite, and clinoptilolite. Minor crandallite group minerals, zircon, and β-form quartz phenocrysts were also found, indicating that volcanic ash was deposited within the peat-forming mires. The presence of augite, hornblende, and smectite group clays in the tonsteins suggests a volcanic source that was intermediate in composition. The higher contents of Ba, F, P, Sr, and Zr in the Franklin coals result from the alteration of volcanic ash in the mires. Apatite contains major amounts of F and P, whereas feldspar contains Ba and Sr. Zircon is the primary Zr-bearing mineral. Crandallite group minerals are major Ba- and P- bearing minerals in the coals and can contain Ca and Sr. Higher As and Hg contents in the coals result from post-Eocene hydrothermal mineralization. Mines in the nearby Green River Gorge contain cinnabar, metacinnabar, realgar, and orpiment. Realgar and orpiment were found in fractured sandstone above the No. 10 coal bed. Kleinite and cinnabar, both mercury-containing minerals, were identified in coal samples and native mercury was found in one parting sample. Thermal and XANES studies on coal samples indicate that there are at least two modes of occurrence for Hg in the Franklin coals: (1) organic complexes containing Hg, and (2) Hg-bearing minerals within the coal and associated partings. Pyrite may also contain trace amounts of As, Hg, and Ni.

X-Ray Diffraction Studies on Structural Changes in Montmorillonite during Dehydration

Montmorillonite, a smectite group clay mineral having 2:1 type of layer structure, possesses different types of structural disorders which have been determined in the present investigation using the Fourier initial slope method and the variance analysis of the X-ray line profiles. The effect of structural changes during dehydration has been studied by heating the samples at several temperatures.

Characterization of a brazilian smectite by solid state NMR and X-ray diffraction techniques

X-ray diffraction (XRD), differential thermal analysis (DTA) and 27Al and 29Si solid state MAS-NMR techniques were used to monitor the fractionation steps of a brazilian smectite, previously crushed, from Campina Grande, Paraíba. The sand, silt and clay fractions were obtained by physical and chemical treatments. The XRD analysis of sand and silt fractions showed that both fractions had predominant quartz and feldspar, respectively. The XRD results of the K+ saturated and heated clay fraction confirmed that the natural clay belongs to the 2:1 clay-mineral group, whereas the analysis of the Mg2+ saturated and glycolated clay fraction confirmed the presence of a smectite group clay. The MAS-NMR results of 27Al and 29Si showed that the sand fraction contains 79% of quartz and the silt fraction contains 55% of quartz, while the clay fraction is rich in smectite with low isomorphic replacement of Si by Al, and contains 38 % of quartz.

Adsorption of 2,2?-bipyridyl onto sepiolite, attapulgite and smectite group clay minerals from anatolia: The FT-IR and FT-Raman spectra of surface and intercalated species

The adsorption of 2,2′-bipyridyl by natural sepiolite, attapulgite, hectorite, saponite and natural and ion exchanged (Mn, Fe, Co, Ni, Cu, Zn or Sn) bentonites has been investigated by FT-IR and FT-Raman spectroscopy. Spectroscopic results indicate that most of the adsorbed molecules are coordinated to either exchangeable cations (in the case of smectite group clays) or Lewis acidic centres (in the case of sepiolite and attapulgite) as bidentate ligands. The formation of monoanionic surface species has also been detected, to a relatively small extent. No physisorbed surface species has been observed. XRD patterns and UV-visible spectra of the samples are also recorded for additional information.

A vibrational spectroscopic study of the adsorption of 4,4?-bipyridyl by sepiolite and smectite group clay minerals from Anatolia (Turkey)

The adsorption of 4,4′-bipyridyl by natural sepiolite and smectite group clay minerals (bentonite, hectorite and saponite) from Anatolia (Turkey) has been studied using vibrational spectroscopy. Investigation of Fourier-transform infrared and Fourier-transform Raman spectra of adsorbed 4,4′-bipyridyl indicate the presence of chemisorbed species. However, any evidence for the generation of anionic species on the surface of the phyllosilicates has not been detected. It is proposed that the adsorbed bipyridyl molecules on sepiolite are centrosymmetric and H-bonded to the surface hydroxyls through both the nitrogen lone pairs as bidentate ligands. The adsorbed bipyridyl molecules on the smectite group clays are coordinated to exchangeable cations both directly and also indirectly through water as monodentate ligands. XRD patterns of the clays studied are also recorded.