clay and mica

Humic acid (HA) is ubiquitous in both terrestrial and aquatic environments, and understanding the molecular interaction mechanisms underlying its aggregation and adsorption is of vital significance. However, the intermolecular interactions of HA-HA and HA-clay mineral systems in complex aqueous environments remain elusive. Herein, the interactions of HA with various model surfaces (i.e., HA, mica, and talc) were quantitatively measured in aqueous media at the nanoscale using an atomic force microscope. The HA-HA interaction was found to be purely repulsive during surface approach, consistent with free energy calculation; during retraction, pH-dependent adhesion was observed due to the protonation/deprotonation of HA that influences the formation of hydrogen bonds. Different from the mica case, hydrophobic interaction was detected for the HA-talc system at pH 5.8, contributing to the stronger HA-talc adhesion, as also evidenced by adsorption results. Notably, HA-mica adhesion strongly depended on the loading force and contact time, most likely because of the short-range and time-dependent interfacial hydrogen bonding interaction under confinement, as compared to the dominant hydrophobic interaction for the HA-talc case. This study provides quantitative insights into the fundamental molecular interaction mechanisms underlying the aggregation of HA and its adsorption on clay minerals of varying hydrophobicity in environmental processes.

Topics: Adsorption; Clay; Humic Substances; Minerals; Talc

Reproducible imaging of DNA by atomic force microscopy was a useful predecessor to Ned Seeman's DNA nanotechnology. Many of the products of DNA nanotechnology were imaged in the atomic force microscope. The mica substrate used in this atomic force microscopy research formed the inspiration for the hypothesis that micaceous clay was a likely habitat for the origins of life. Montmorillonite clay has been a successful substrate for the polymerization of amino acids and nucleotides into peptides and DNA oligomers in research on life's origins. Mica and montmorillonite have the same anionic lattice, with a hexagonal spacing of 0.5 nm. Micas are nonswelling clays, with potassium ions (K

Topics: Bentonite; Clay; DNA; Ions; Sodium

Today the terrestrial surface drives biogeochemical cycles on Earth through chemical weathering reactions mediated by the biological influence of soils. Prior to the expansion of life on to land, abiotic weathering may have resulted in different boundary conditions affecting the composition of the biosphere. Here we show a striking difference in weathering produced minerals preserved in the Mesoproterozoic Velkerri Formation. While the bulk chemistry and mineralogy is dominated by illite similar to many modern mudstones, application of a novel microbeam technology reveals that the initial detrital minerals were composed of mica (28%) and feldspar (45%) with only a trace amount (<2%) of typical soil formed clay minerals. The majority of illite and the high Al

Topics: Aluminum Silicates; Australia; Chemical Phenomena; Chemistry, Physical; Clay; Environmental Monitoring; Geological Phenomena; Geology; Minerals; Oceans and Seas; Potassium Compounds; Soil; Trace Elements; Weather

A new class of nanohybrids composed of structurally exfoliated silicate platelets and magnetic iron oxide nanoparticles was synthesized and shown to be capable of capturing microbes in liquid microbiological media. Nanoscale silicate platelets with an approximate thickness of 1.0 nm were prepared from the naturally occurring mineral clays montmorillonite and mica; these clays yielded platelets with lateral dimensions on the order of 80-100 nm and 300-1000 nm, respectively. The magnetic Fe3O4 nanoparticles, approximately 8.3 nm in diameter, were coated in situ onto the silicates during the synthesis process, which involved the coprecipitation of aqueous Fe(2+)/Fe(3+) salts. Owing to the high surface area-to-volume ratios and the presence of ionically charged groups (i.e., ≡SiO(-)Na(+)), the silicate nanoplatelets exhibited intense noncovalent bonding forces between Fe3O4 nanoparticles and the surrounding microorganisms. The Fe3O4-on-nanoplatelet nanohybrids enabled the entrapment of bacterial cells in liquid microbiological media. These captured bacteria formed bacterial aggregates on the order of micrometers that became physically maneuverable under a magnetic field. This phenomenon was demonstrated with Staphylococcus aureus in liquid microbiological media by physically removing them using a magnetic bar; in two experimental examples, bacterial concentrations were reduced from 10(6) to 10(2) and from 10(4) to 10(0) CFU/mL (colony formation unit/mL con). Under a scanning electron microscope, these bacteria appeared to have rough and wrinkled surfaces due to the accumulated silicate platelets. Furthermore, the external application of a high-frequency magnetic field completely destroyed these aggregated microbes by the magnetically induced heat. Hence, the newly developed nanohybrids were shown to be viable for physically capturing microbes and also for potential hyperthermia treatment applications.

Topics: Aluminum Silicates; Bacteria; Chemical Precipitation; Clay; Colony Count, Microbial; Escherichia coli; Ferric Compounds; Hot Temperature; Magnetic Fields; Magnetics; Microbial Viability; Nanoparticles; Particle Size; Silicates; Staphylococcus aureus; X-Ray Diffraction

The processing and characterization of multifunctional nanobiocomposite of biodegradable poly[(butylene succinate)-co-adipate] (PBSA) and organically modified synthetic fluorine mica (OSFM) are reported. The nanobiocomposite of PBSA with OSFM was prepared using melt- blending, and the structure and morphology of the nanocomposite were characterized using X-ray diffraction and transmission electron microscopy. The mechanical and material properties measurements showed the concurrent improvement in temperature dependence storage modulus, tensile properties, gas barrier, and thermal stability of neat PBSA after nanocomposite formation. Such improved inherent properties along with the environmentally-friendly feature are expected to widen the use of PBSA for short-term food-packaging applications.

Topics: Adipates; Aluminum Silicates; Butylene Glycols; Clay; Fluorine; Nanocomposites; Polymers

Effect of intense rainfall on the distribution of Fukushima-accident-derived (137)Cs in soil was examined. Inventories and vertical distributions of (137)Cs in soils were determined at 15 locations (including croplands, grasslands, and forests) in Fukushima city in the post-rainy season, approximately 4.5months after the accident, and were compared with those in the pre-rainy season determined in our former study. The (137)Cs inventory levels scarcely changed between points in time spanning the first rainy season after the accident. Moreover, the majority of (137)Cs remained stored in the aboveground vegetation and in the upper 5cm of soil layer at undisturbed locations in the post-rainy season. A more quantitative analysis with the characterization of the vertical profile of (137)Cs using the relaxation length confirmed that the vertical profile was almost unchanged at most locations. Accordingly, it is concluded that rainfall during the rainy season had a limited effect on (137)Cs distribution in the soil, indicating the very low mobility. Chemical extraction of (137)Cs from selected soil samples indicated that (137)Cs in the soil was barely water soluble, and even the fraction extracted with 1M ammonium acetate was only approximately 10%. This further supports the low mobility of (137)Cs in our soils. Soil mineralogical analyses, which included the identification of clay minerals, suggested that smectite and mica could lower the exchangeable fraction of (137)Cs. However, no direct relationship was obtained between mineral composition and (137)Cs retention in the upper soil layer. In contrast, positive correlations were observed between (137)Cs extractability and soil properties such as pH, organic matter content, finer-sized particle content, and cation-exchange capacity. These results suggest that the mineralogical effect on the firm fixation of (137)Cs on soil constituents may be masked by the non-specific adsorption offered by the physicochemical properties of the soils.

Topics: Aluminum Silicates; Cesium Radioisotopes; Clay; Fukushima Nuclear Accident; Radiation Monitoring; Rain; Seasons; Silicates; Soil; Soil Pollutants, Radioactive; Trees

To ensure efficiency and sustainability of geologic CO2 sequestration (GCS), a better understanding of the geochemical reactions at CO2-water-rock interfaces is needed. In this work, both fluid/solid chemistry analysis and interfacial topographic studies were conducted to investigate the dissolution/precipitation on phlogopite (KMg3Si3AlO10(F,OH)2) surfaces under GCS conditions (368 K, 102 atm) in 1 M NaCl. Phlogopite served as a model for clay minerals in potential GCS sites. During the reaction, dissolution of phlogopite was the predominant process. Although the bulk solution was not supersaturated with respect to potential secondary mineral phases, interestingly, nanoscale precipitates formed. Atomic force microcopy (AFM) was utilized to record the evolution of the size, shape, and location of the nanoparticles. Nanoparticles first appeared on the edges of dissolution pits and then relocated to other areas as particles aggregated. Amorphous silica and kaolinite were identified as the secondary mineral phases, and qualitative and quantitative analysis of morphological changes due to phlogopite dissolution and secondary mineral precipitation are presented. The results provide new information on the evolution of morphological changes at CO2-water-clay mineral interfaces and offer implications for understanding alterations in porosity, permeability, and wettability of pre-existing rocks in GCS sites.

Topics: Aluminum Silicates; Carbon Dioxide; Chemical Phenomena; Chemical Precipitation; Clay; Geological Phenomena; Salts

This is the first test of a highly charged swelling mica's (Na-2-mica) ability to reduce the plant-absorbed Cu in Cu-contaminated soils from Chile. Perennial ryegrass (Lolium perenne L.) was grown in two acid soils (Sector 2: pH 4.2, total Cu = 172 mg Cu kg(-1) and Sector 3: pH 4.2, total Cu = 112 mg Cu kg(-1)) amended with 0.5% and 1% (w/w) mica, and 1% (w/w) montmorillonite. At 10 weeks of growth, both mica treatments decreased the shoot Cu of ryegrass grown in Sector 2 producing shoot Cu concentrations above 21-22 mg Cu kg(-1) (the phytotoxicity threshold for that species), yet the mica treatments did not reduce shoot Cu concentrations when grown in Sector 3, which were at a typical level. The mica treatments improved shoot growth in Sector 3 by reducing free and extractable Cu to low enough levels where other nutrients could compete for plant absorption and translocation. In addition, the mica treatments improved root growth in both soils, and the 1% mica treatment reduced root Cu in both soils. This swelling mica warrants further testing of its ability to assist re-vegetation and reduce Cu bioavailability in Cu-contaminated surface soils.

Topics: Aluminum Silicates; Biomass; Clay; Copper; Environmental Restoration and Remediation; Industrial Waste; Lolium; Plant Roots; Plant Shoots; Soil Pollutants; Time Factors

The dispersion and gelation of clay suspensions have major impact on a number of industries, such as ceramic and composite materials processing, paper making, cement production, and consumer product formulation. To fundamentally understand controlling mechanisms of clay dispersion and gelation, it is necessary to study anisotropic surface charge properties and colloidal interactions of clay particles. In this study, a colloidal probe technique was employed to study the interaction forces between a silica probe and clay basal plane/edge surfaces. A muscovite mica was used as a representative of 2:1 phyllosilicate clay minerals. The muscovite basal plane was prepared by cleavage, while the edge surface was obtained by a microtome cutting technique. Direct force measurements demonstrated the anisotropic surface charge properties of the basal plane and edge surface. For the basal plane, the long-range forces were monotonically repulsive within pH 6-10 and the measured forces were pH-independent, thereby confirming that clay basal planes have permanent surface charge from isomorphic substitution of lattice elements. The measured interaction forces were fitted well with the classical DLVO theory. The surface potentials of muscovite basal plane derived from the measured force profiles were in good agreement with those reported in the literature. In the case of edge surfaces, the measured forces were monotonically repulsive at pH 10, decreasing with pH, and changed to be attractive at pH 5.6, strongly suggesting that the charge on the clay edge surfaces is pH-dependent. The measured force profiles could not be reasonably fitted with the classical DLVO theory, even with very small surface potential values, unless the surface roughness was considered. The surface element integration (SEI) method was used to calculate the DLVO forces to account for the surface roughness. The surface potentials of the muscovite edges were derived by fitting the measured force profiles with the surface element integrated DLVO model. The point of zero charge of the muscovite edge surface was estimated to be pH 7-8.

Topics: Aluminum Silicates; Clay; Colloids; Hydrogen-Ion Concentration; Hydroxyl Radical; Microscopy, Atomic Force; Microscopy, Electron, Scanning; Models, Statistical; Molecular Conformation; Poisson Distribution; Silicon Dioxide; Stress, Mechanical; Surface Properties; X-Ray Diffraction

Smelting of copper (Cu) results in the atmospheric deposition of Cu onto surrounding soils. Excess concentrations of Cu in soils can be absorbed by soil biota to toxic levels or leached into the groundwater, threatening the entire ecosystem. A means to restrict Cu mobility and uptake by plants is to remove it from the aqueous phase by applying an adsorptive material. A synthetic clay (highly charged swelling mica) was tested for its ability to decrease the levels of free and 0.1 M KNO3-extractable Cu in 15 surface soils from three different Cu mining areas in central Chile. The soils contained excessive total Cu levels (112-2790 mg Cu (kg soil)(-1)), while extractable Cu ranged from 0.3 to 22.9 mg Cu L(-1). The mica was applied to each soil at rates of 0.1%, 1%, and 2% (w/w). A 2% sodium-montmorillonite treatment and the nonamended soil served as controls. The order of treatment efficacy in reducing extractable Cu and free Cu2+ for low pH soils ( 1% mica > 2% montmorillonite > 0.1% mica. At 120 days, the 2% mica treatment maintained reductions of up to 93% in the free Cu2+ activity and up to 75% in the extractable Cu concentration upon acidification to the original soil pH value. In addition, Cu retention in mica-treated soils was more resistant to acidification than in lime-treated soils. This mica has promise for the remediation of acidic soils with metal contamination at the surface.

Topics: Acids; Aluminum Silicates; Clay; Copper; Hydrogen-Ion Concentration; Soil; Soil Pollutants; Time Factors

There is a need to develop highly CU2+ selective materials which can potentially remediate copper contaminated soils and water. Here we show that several highly charged synthetic swelling mica-type clays are highly selective for copper exchange. The synthetic micas have cation exchange capacities (CECs), which are close to their theoretical values. Both Na-saturated and Mg-saturated micas were investigated for Cu ion exchange selectivity. Ion exchange isotherms and Kielland plots were constructed using the equilibrated solution analyses. From these studies it was found that Na-4-mica and Na-3-mica could selectively exchange copper at lower concentrations from solution, whereas Na-2-mica sample performed better by showing Cu ion exchange selectively to almost its capacity. The EPR spectra of Cu-exchanged micas coincide with the mica's charge characteristics that predict increased binding strength of exchangeable Cu in Na-4-mica and Na-3-mica than in Na-2-mica.

Topics: Aluminum Silicates; Clay; Copper; Fluorides; Ion Exchange; Kaolin; Magnesium Chloride; Magnesium Compounds; Silica Gel; Silicon Dioxide; Sodium Chloride; Soil Pollutants; Waste Management

In a recent study (Energy Fuels 2005, 19, 936), a partially hydrolyzed polyacrylamide (HPAM) was used as a process aid to recover bitumen from oil sand ores. It was found that HPAM addition at the bitumen extraction step not only improved bitumen recovery but also enhanced fine solids settling in the tailings stream. To understand the role of HPAM, single-molecule force spectroscopy was employed for the first time to measure the desorption/adhesion forces of single HPAM molecules on silica, mica, and bitumen surfaces using an atomic force microscope (AFM). Silicon wafers with an oxidized surface layer and newly cleaved mica were used, respectively, to represent sand grains and clays in oil sands. The force measurements were carried out in deionized water and in commercial plant process water under equilibrium conditions. The desorption/adhesion forces of HPAM obtained on mica, silica, and bitumen surfaces were approximately 200, 40, and 80 pN in deionized water and approximately 100, 50, and 40 pN in the plant process water, respectively. The measured adhesion forces together with the zeta potential values of these surfaces indicate that the polymer would preferentially adsorb onto clay surfaces rather than onto bitumen surfaces. It is the selective adsorption of HPAM that benefits both bitumen recovery and tailings settling when the polymer was added directly to the bitumen extraction process at an appropriate dosage.

Topics: Acrylic Resins; Adsorption; Aluminum Silicates; Clay; Hydrocarbons; Petroleum; Silicon Dioxide

Topics: Adsorption; Aluminum Silicates; Clay; Environmental Pollution; Manufactured Materials; Radium; Soil Pollutants, Radioactive; Water Pollutants, Radioactive

The effects of silicic acid, silica and clay minerals on the conversion of amorphous calcium phosphate to hydroxyapatite (HAP) were studied in vitro by a pH drop method. At a concentration range of 0.01-0.1 mM. silicic acid stimulated the rate of HAP transformation by about 30-40%. Silica stimulated the rate of HAP transformation by 33-43% at a concentration range of 0.05-1.5 mg/ml. The clay minerals, i.e. kaolin and talc, also stimulated the rate of HAP transformation by 40-90% at a concentration range of 0.4-10 mg/ml, but mica inhibited the reaction markedly at 10 mg/ml. The distribution of silicon in human supragingival dental calculus was studied by an electron-probe microanalyser. We found localized silicon distribution on the oral surface of the calculus. Such silicon-rich areas always contained silicon either alone or together with magnesium, aluminium, potassium, calcium and iron. This implies that the silicon-rich area may be opal and mica. Because silicic acid, silica, kaolin and talc stimulated and mica inhibited the in vitro calcium phosphate precipitation, it is possible that these silicon-rich areas may regulate the formation of the dental calculus.

Topics: Adult; Aged; Aluminum Silicates; Calcium; Calcium Phosphates; Chelating Agents; Chemical Precipitation; Child; Clay; Dental Calculus; Durapatite; Electron Probe Microanalysis; Female; Humans; Hydrogen-Ion Concentration; Hydroxyapatites; Male; Middle Aged; Minerals; Phosphates; Phosphorus; Silicic Acid; Silicon; Silicon Dioxide

Fourier transform i.r. measurements of L-pyroglutamic acid dispersed in a matrix of a clay, silica or alumina have been obtained at various temperatures between 25 and 220 degrees C. The i.r. spectrum of L-pyroglutamic acid varies in a manner dependent upon the matrix material and shows considerable change as the temperature of the mixtures is increased. The differences in the spectrum at elevated temperatures are explained in terms of a chemical reaction between hydroxyl groups in the matrix and the carboxylic acid. The i.r. spectra of trimethylsilyl derivatives of L-pyroglutamic acid and aluminum pyroglutamate were also measured to assist the understanding of spectra and interpretation of the spectral changes dependent upon increasing temperature.

Topics: Aluminum Oxide; Aluminum Silicates; Amino Acids; Bentonite; Clay; Hot Temperature; Kaolin; Magnesium Compounds; Minerals; Pyrrolidonecarboxylic Acid; Silicon Compounds; Silicon Dioxide; Spectroscopy, Fourier Transform Infrared; Spectrum Analysis, Raman