Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Clay”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources
PubMed2003

Enhancing phosphate removal from wastewater by using polyelectrolytes and clay injection.

Aluminum sulfate, alum, is a common chemical coagulant used for coagulation. Recently, polymers have been utilized in coagulation/flocculation processes for water purification. In this study, the ability of two organic polymers, tannin (natural polyelectrolyte) and AN913 (synthetic anionic polyelectrolyte), and clay to act as coagulant aids was tested, in the removal of phosphate from synthetic wastewater. Contaminants in synthetic waters were coagulated using alum, alum+clay, alum+tannin, alum+AN913, alum+tannin+clay and alum+AN913+clay. Alum together with polymers as coagulant aids yielded a significant improvement in phosphate removal compared with alum alone, for initial phosphate concentrations of 5-15 mg/l PO(4)(3-). The use of clay and polyelectrolytes improved the efficiency of phosphate removal and lowered the required alum dose. Fourier transform infrared (FTIR) spectroscopy was used for the identification and characterization of the aluminum species formed during dephosphorization of the synthetic wastewater with and without tannin, AN913 and clay. Evidence from FTIR spectroscopy showed the formation of aluminum hydroxyphosphate, hydroxy-Al-tannate and aluminum complexes containing phosphorus, tannin and AN913.

Alum Compounds↗
PubMed2003

Velocity measurement of clay intrusion through a sudden contraction step using a tagging pulse sequence.

Magnetic resonance imaging (MRI) with a spatial tagging sequence was used to measure the velocity distribution of clay that was forced past a sudden contraction. A spatial tagging sequence provided magnetic resonance images of clay that allowed measurement of the velocity distribution in the clay, which can provide profound insights on the deformation process of clay during the intrusion process. The experiments were conducted using a specially-designed vessel that could operate at up to 30 MPa. The vessel offers a rectangle test section with a sudden contraction step that had a ratio of contraction of 2:1. The vessel was installed into a commercial magnetic resonance imaging equipment and then the fluid motion of clay flowing into the narrow contracted channel was quantitatively investigated to examine behaviors of flowing clay as non-Newtonian fluid. MRI results are compared with those obtained by computational fluid dynamics (CFD) calculation. Velocity distributions obtained from each tag displacement did not well agree with those predicted by CFD results near the contraction step where the fluid accelerated rapidly. However, a post-processing on calculation results, in which virtual tag displacement is calculated, gave better agreement with experiment and enabled us to compare MRI results with CFD results.

Aluminum Silicates↗
PubMed2002

A hydrogen biosensor made of clay, poly(butylviologen), and hydrogenase sandwiched on a glass carbon electrode.

A hydrogen gas (H(2)) biosensor was developed in which hydrogenase (H(2)ase) was immobilized and sandwiched between two layers of a montmorillonite clay and poly(butylviologen) (PBV) mixture on a glass carbon electrode. The immobilized PBV efficiently enhanced the electron transfer among the electrode, H(2)ase, and methyl viologen in solution. Both PBV and methyl viologen acted as the electron carrier in the clay-PBV-H(2)ase modified electrode. The clay-PBV-H(2)ase electrode catalyzed the oxidation of H(2) to protons (H(+)) with the electrons being transferred by viologen groups to the electrode. The activation energy of this process was 38+/-2 kJ/mol at pH 7. The catalytic current of the clay-PBV-H(2)ase electrode increased linearly when exposed to increasing concentrations of H(2) gas. In contrast, this electrode showed no activity when exposed to three combustible compounds, namely, carbon monoxide, methane and methanol. The optimum pH range for the oxidation of H(2) by the clay-PBV-H(2)ase electrode was from 7 to 10. Electron transfer process in the clay-PBV-H(2)ase electrode is discussed.

Aluminum Silicates↗
PubMed2004

Enhanced reduction of Cr(VI) by direct electric current in a contaminated clay.

The probable relation between diffuse double-layer processes and redox reactions that enhance degradation or conversion of contaminants under an applied electric field were examined in a clay medium. Kaolinite clay, precontaminated with hexavalent chromium, was the test soil medium. Analyte, containing ferrous iron, was transported through the kaolinite clay using direct electric current. The Cr(VI) reduction to Cr(III) was followed by measuring the soil redox potential and pH at discrete locations in the clay bed. The post-test distribution of Cr showed significantly more Cr(III) than Cr(VI) at low to slightly acidic pH distribution (2 < pH < 6) in clay. The stoichiometric analyses of measured chromium and iron species concentrations versus the measured redox potentials were compared to Nernst equation predictions of an equivalent aqueous system. An average of +0.37 V shift was measured from the linear Nernstian prediction of cell potential. The applied electric field appeared to provide additional "cathodic current" to drive forth the redox reactions. The redox potential shift was explained by possible overpotential development at the clay-water interfaces due to double-layer polarization under the applied field.

Aluminum Silicates↗
PubMed2005

High resolution electron microscopy structural studies of organo-clay nanocomposites.

Engineering of clay nanocomposite materials by modification of their surfaces can enable the control of retention, transport, and persistence of toxic chemicals in the geosystem. The properties and interactions of clay nanocomposites have been widely studied, but little information exists on their microstructure at a range of scale extending down to atomic dimensions. The pairing of Na-montmorillonite clay with organic cations as well as with the herbicide fluridone, chosen as a model for an organic pollutant, was studied. Three organic cations were selected: hexadecyltrimethylammonium, benzyltrimethylammonium, and benzyltriethylammonium at 0%, 60%, and 100% of cation exchange capacity (CEC) loadings. A detailed microstructural analysis of the organo-clay nanocomposites and of the fluridone nanocomposites was undertaken by high-resolution transmission electron microscopy (HRTEM) and X-ray energy-dispersive spectroscopy (EDS). Morphological observations and chemical analyses were performed simultaneously on the same sample. The combined HRTEM and EDS measurements strongly suggest (a) heterogeneous local intercalation of the organic cations manifested by a range in the measured d001 spacing, implying random expansion of the clay layered structure with increased loading of the organic cations; (b) intercalation within the external layers, which is thoroughly influenced by local defect microstructure and/or edge availability of the montmorillonite nanoparticles as well as by the molecular structure of the intercalating organic cation. Additional intercalation of fluridone molecules did not affect the structure (d001 spacing) of the organo-clay nanocomposites.

Aluminum Silicates↗
PubMed2006

Enhanced sorption of trichloroethene by smectite clay exchanged with Cs+.

Trichloroethene (TCE) is one of the most common pollutants in groundwater, and Cs+ can be a cocontaminant at nuclear facilities. Smectite clays have large surface areas, are common in soils, have high affinities for some organic contaminants, and hence can potentially influence the transport of organic pollutants entering soils and sediments. The exchangeable cations present near smectite clay surfaces can radically influence the sorption of organic pollutants by soil clays. This research was undertaken to determine the effect of Cs+, and other common interlayer cations, such as K+ and Ca2+, on the sorption of TCE by a reference smectite clay saponite. Cs-saturated clay sorbed the most TCE, up to 3500 mg/kg, while Ca-saturated smectite sorbed the least. We hypothesize that the stronger sorption of TCE by the Cs-smectite can be attributed to the lower hydration energy and hence smaller hydrated radius of Cs+, which expands the lateral clay surface domains available for sorption. Also, Cs-smectite interlayers are only one or two water layers thick, which may drive capillary condensation of TCE. Our results implicate enhanced retention of TCE in aquifer materials containing smectites accompanied by Cs+ cocontamination.

Adsorption↗
PubMed2004

Clay-vesicle interactions: fluorescence measurements and structural implications for slow release formulations of herbicides.

Clay-vesicle systems exhibit a potential for environmental applications, such as herbicide formulations for reduced leaching. Clay-vesicle interactions were addressed by combining adsorption and XRD measurements with fluorescence studies for didodecyldimethylammonium bromide (DDAB), dioctadecyldimethylammonium bromide (DDOB), and montmorillonite. XRD and adsorption data indicated that the adsorbing vesicles were transformed after 3 days into paraffinic and bilayer structures. Fluorescence studies revealed that adsorption was almost complete within 5 min for a loading below the cation exchange capacity (CEC). Aggregation and sedimentation of clay-surfactant particles occurred within several minutes. Fluorescent measurements of supernatants indicated decomposition of vesicles at a high clay/surfactant ratio due to rapidly adsorbing cationic monomers. The kinetics of energy transfer between vesicles labeled by NBD-PE (1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl)) and montmorillonite labeled by rhodamine-B follows that of aggregation of surfactant-clay particles and structural changes of the vesicles at times of minutes to hours. Experiments following the reduction of NBD fluorescence by addition of dithionite indicate faster permeabilization of DDOB than DDAB vesicles, which was confirmed by leakage experiments. The faster permeabilization of DDOB vesicles in the presence of clay was correlated with their inferior suitability for the preparation of clay-based formulations of anionic herbicides for slow release.

Adsorption↗
PubMed2006

A molecular model for epsilon-caprolactam-based intercalated polymer clay nanocomposite: Integrating modeling and experiments.

In studying the morphology, molecular interactions, and physical properties of organically modified montmorillonite (OMMT) and polymer clay nanocomposites (PCNs) through molecular dynamics (MD), the construction of the molecular model of OMMT and PCN is important. Better understanding of interaction between various constituents of PCN will improve the design of polymer clay nanocomposite systems. MD is an excellent tool to study interactions, which require accurate modeling of PCN under consideration. Previously, the PCN models were constructed by different researchers on the basis of specific criteria such as minimum energy configuration, density of the polymer clay nanocomposite, and so forth. However, in this article we describe the development of models combining experimental and conventional molecular modeling to develop models, which are more representative of true intercalated PCN systems. The models were used for studying the morphological interactions and physical properties. These studies gave useful information regarding orientation of organic modifiers, area of coverage of organic modifiers over the interlayer clay surface, interaction of organic modifiers with clay in OMMT, interaction among different constituents of PCN, conformational and density change, and actual proportion of mixing of polymer with clay in PCN. We have X-ray diffraction and photoacoustic Fourier transform infrared spectroscopy to verify the model.

Aluminum Silicates↗
PubMed2003

Effect of expandable clays and cometabolism on PAH biodegradability.

Pyrene and phenanthrene degradation was examined in both single and binary slurry systems for three different natural soils. It was found that the amount of total expandable clays (smectite and vermiculite) was in a good agreement with the achieved rate and extent of biodegradation. For instance, the intrinsic phenanthrene biodegradation rate was 626 microg/L/day for the soil with the largest expandable clay and 3203 microg/L/day for the soil with the least. Similarly, the smallest total pyrene biodegradation (65%) was found for the soil rich in expandable clays, compared to an 82% pyrene reduction in the soil that had the lowest amount. Mass transfer limitation after compound sorption to the clays was more pronounced for the more hydrophobic pyrene. In the presence of phenanthrene, total pyrene biodegradation increased by 2 to 7% due to cometabolism, while the total phenanthrene biodegradation was only enhanced by 0.5 to 5% in the binary system. This research demonstrated that expandable clays might govern the substrate availability to microorganisms and microbial accessibility to substrates. Therefore, the contribution of organic matter and expandable clays to sorption, desorption and biodegradation should be taken equally into account in order to better understand complex bioremediation issues.

Aluminum Silicates↗
PubMed1991

Protection of Nitrosomonas europaea colonizing clay minerals from inhibition by nitrapyrin.

Nitrate production by Nitrosomonas europaea in inorganic liquid medium containing ammonium was limited by reduction in pH. In the presence of montmorillonite and vermiculite, expanding clays with high cation-exchange-capacity (CEC), nitrite yield was increased, ammonia oxidation continued at pH values below those which inhibited growth in the absence of clays and growth was biphasic. The first phase was similar to that in the absence of clays, while the second was characterized by a lower rate of nitrite production. Illite, a non-expanding clay with low CEC, had no significant effect on ammonia oxidation, while oxidation of ammonia-treated vermiculite (ATV) occurred with no significant change in the pH of the medium. ATV, montmorillonite and vermiculite, but not illite, protected cells from inhibition by nitrapyrin at concentrations inhibitory to cells growing in suspended culture. This protection was maintained in ATV homo-ionic to Al3+, but montmorillonite made homo-ionic to Al3+ did not provide protection from inhibition. Attachment of cells to clays with high CEC is therefore advantageous in providing exchange at the clay surface of NH+4 and H+ produced by ammonia oxidation, in reducing pH toxicity, and in protecting cells from inhibition.

Aluminum Silicates↗
PubMed2000

Clay minerals protect bacteriophage PBS1 of Bacillus subtilis against inactivation and loss of transducing ability by UV radiation.

The effect of UV radiation on the survival of and transduction by phage PBS1 of Bacillus subtilis, free or adsorbed on the clay minerals montmorillonite (M) and kaolinite (K), was studied. After free or clay-associated phage (approximately 10(7) PFU.mL-1) was irradiated with UV light (254 nm) for 0, 1, 2, 5, 10, and 30 min and then allowed to infect B. subtilis FB300 (thiB4 metA29 argF4 Rfmr), the phage was titered, and Met+ transductants were enumerated on selective media. After 1 min of irradiation, the titer of free and clay-associated phage decreased significantly (approximately 1.6 times for free phage, and approximately 4.9 and 6.8 times for M and K, respectively), whereas the transduction frequency increased significantly (approximately 3 times for free phage and approximately 1.4 and 2.2 times for M and K, respectively). The titer and transduction frequency of clay-associated phage remain essentially constant between 1 and 10 min of irradiation, whereas the titer of free phage decreased by approximately 1 order of magnitude after 5 min of irradiation. When free phage was irradiated for 10 min, the titer and transduction frequency decreased by approximately 2 and 0.5 orders of magnitude, respectively, whereas 30 min of irradiation was necessary to obtain comparable decreases with clay-associated phage. These results indicated that phages are protected to some extent from UV radiation when adsorbed on clay minerals.

Aluminum Silicates↗
PubMed2003

[Extinguishment of harmful algae by organo-clay].

Periodic and widespread algal blooms have caused a variety of problems for aquatic life and human activity throughout the world. Currently, the only remedial practice employed for removing algal blooms is to spread clay on the surface of the water. But, the algal removal efficiency by the crude minerals are not really ideal, and how to improve the capability of clays to remove algae is now the technological focus, which also is fatal to the practical value of clays. In this study, hexadecyltrimethyleamine bromide (HDTMAB), one kind of cationic organo-surfactants, was chosen to improve kaolin by surface sorption and cationic exchange, and was tested to remove Prorocentrum donghaiense, a red tide organism in Donghai Sea. The results indicated that organo-clay had an excellent ability to extinguish red tide organisms, even under the application of 0.01 g.L-1, and could subside more than 95% red tide organisms in 24 h. The efficient algae removal by organo-clay might be from the reversal of the surface electric charge on clay particles, the "net capture" by the long lipoid chains of HDTMAB, and the local high density of HDTMAB on particles surface, which could effectively kill algal cells.

Aluminum Silicates↗
PubMed2005

[Effects of ionic strength on the flocculation and removal of cyanobacterial cells of Microcystis aeruginosa by clays].

The effect of ionic strength on the flocculation and removal of Microcystis aeruginosa by clays and chitosan-modified clays were studied. High ionic strength was beneficial to the removal of algae cells by clays due to the reduction of the thickness of electrical double layer that enhanced the collision probability of the granules. In contrast to normal clays, chitosan-modified clays showed a higher removal efficiency of Microcystis aeruginosa cells under low ionic strength. The removal efficiency was reduced from more than 90% to 70% by sepiolite, but promoted from 70% to 95% by modified sepiolite when the ionic strength decreased from 0.17mol/L to 0 mol/L. This is because the repulsion of positive charged groups in chitosan molecule chain were shielded by large number of ions at higher ionic strength that reduce the extensibility of the chitosan molecule, leading to the reduction of bridging and netting between particles. Chitosan-modified clays were therefore suitable for removal cyanobacterial cells in fresh waters such as lakes, reservoirs and rivers.

Adsorption↗
PubMed1995

Hydroxyapatite clay used to fill the gap between implant and bone.

A clay containing hydroxyapatite (HA) was developed for use as a filling material between an uncemented implant and bone. It consists of 55% HA granules greater than 0.1 mm in size with a homogeneous pore distribution and a porosity of 35% to 48% in a saline solution of sodium alginate (6%). Ti-6A1-4V alloy rods with smooth surfaces were implanted into the distal medullary canal of one osteotomised tibia of 32 Japanese white rabbits. Sixteen rods were inserted with HA clay and 16 without the clay to act as a control group. Six of each group were killed at one week and ten at 12 weeks postoperatively. The pull-out strength of the implants with HA clay was significantly greater at 12 weeks (p < 0.05), as was the percentage of the area of the new bone (p < 0.05). The study suggests that HA clay has an osteoconductive property, allowing adequate bone fixation across a gap at an early stage. The use of HA clay to enhance the early stability of uncemented components may help to improve the functional outcome of total joint arthroplasty.

Alloys↗
PubMed1976

Clays as possible catalysts for peptide formation in the prebiotic era.

From the point of view of prebiotic synthesis, clays might have performed functions of concentration, catalysis, and protection of molecules. The degree of polymerization obtained when amino acid adenylates are added to montmorillonite suspensions in water, are much iigher than those obtained by polymerization in the absence of such a clay. In addition, they are of a discrete spectrum, usually multiplies of 6 or 7, and reach values of up to 40 mers. In the absence of clay a continuous spectrum of degrees of polymerization is obtained, and usually up to 4-6 mers only. Copolymerization in the absence of clays yields mostly random copolymers in their presence mostly block copolymers are obtained. Optical density measurements show that after adsorption has taken place on the clay, stacking of its layers occurs. Polymerization starts only after these stacked layers have been formed. The distance between the layers - as measured by X-rays - increase during polymerization, probably because the resulting polymers settle in their interspace, while the adsorption site of the active monomers is at the edges of the clay.

Adenosine Monophosphate↗
PubMed1989

Mineral catalysis of the formation of the phosphodiester bond in aqueous solution: the possible role of montmorillonite clays.

The binding of adenosine to Na(+)-montmorillonite 22A is greater than 5'-AMP, at neutral pH. Adenine derivatives bind more strongly to the clay than the corresponding uracil derivatives. These data are consistent with the protonation of the adenine by the acidic clay surface and a cationic binding of the protonated ring to the anionic clay surface. Other forces must be operative in the binding of uracil derivatives to the clay since the uracil ring system is not basic. The reaction of the 5'-AMP with water soluble carbodiimide in the presence of Na(+)-montmorillonite results in the formation of 2',5'-pApA (18.9%), 3',5'-pApA (11%), and AppA (4.8%). When poly(U) is used in place of the clay the product yields are 2',5'-pApA (15.5%), 3',5'-pApA (3.7%) and AppA (14.9%). The cyclic nucleotide, c(pA)2 is also formed when poly(U) is used. AppA is the principal reaction product when neither clay nor poly(U) is present in the reaction mixture. When 2'-deoxy-5'-AMP reacts with carbodiimide in the presence of Na(+)-montmorillonite 22A the products are dpApA (4.8%), dAppApA (4.5%) and dAppA (17.4%). Cyclic 3',5'-dAMP is the main product (14%) of the reaction of 2'-deoxy-3'-AMP.

Adenine↗
PubMed2004

The titration of clay minerals I. Discontinuous backtitration technique combined with CEC measurements.

Previous experimental studies on clay potentiometric titration have been unable to distinguish inorganic cation exchange in the interlayer and on basal plane surfaces from specific pH-dependent sorption of cations and anions on the edges. In this study, we refined a titration technique, combining discontinuous backtitration and cation exchange capacity (CEC) measurements, and applied it to the potentiometric titration of Na- and Ca-conditioned montmorillonites. This technique can be used to accurately measure cation exchange, edge surface proton charge, dissolution of clay, and precipitation of new phases. Thus, a precise measurement of the variations of net proton surface charge is possible. This has important implications for clay surface modeling (see part II of this article) and for processes that depend on the clay surface charge, e.g., alteration, rheological processes, and contamination retention applications. In addition, this study confirms the adsorption of ionic pairs such as CaCl+ in exchange site positions and shows that CaOH+ could behave like CaCl+. This result, together with the evidence of precipitation of a Ca?Si phase over a short time-scale (1 week) at high pH and low temperature, can be used to model clay-concrete interactions more accurately. We confirmed and quantified the H+/Na+ exchange reaction at low pH. Finally, we demonstrate that both the edge surface charge and the permanent structural charge are compensated for by the nonspecific sorption of cations from solution across the entire pH range from 4 to 11. Under these conditions, the surface potential is fully screened and does not need to be invoked in modeling sorption processes on clay particles in dilute suspensions.

Journal Article↗
PubMed2004

Effect of dialysis treatment on the aggregation state of montmorillonite clay.

In this work dialysis was used as a technique to modify the aggregation state of montmorillonite clay. Na-montmorillonite clay suspension was treated by a dialysis process and the effect of dialysis time on the surface area of the treated clay was studied. In a clay suspension, a decrease in cation content increases the interparticle repulsion forces exponentially, leading to separation of clay into the elementary clusters of layers by osmotic swelling. During dialysis treatment, the classical delamination process and mechanism were not observed. According to N(2) adsorption isotherms, the increase of surface area concerns to the development of mesoporosity. Nevertheless, the surface area increase cannot be explained by the delamination or exfoliation of some layers, since an increase in the expected number of layers that would yield the surface area does not explain the mesoporosity observed after dialysis. Based on these results, a new mechanism of evolution of the clay aggregation state after dialysis and drying is proposed.

Journal Article↗