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1.
Donald Mkhonto Phuti E. Ngoepe Timothy G. Cooper Nora H. de Leeuw 《Physics and Chemistry of Minerals》2006,33(5):314-331
Computer modelling techniques were employed to investigate the adsorption of a selection of organic surfactant molecules to a range of fluorapatite surfaces, and new interatomic potential models for the apatite/adsorbate interactions are presented. The adsorbates coordinate mainly to the surfaces through interaction between their oxygen (or nitrogen) atoms to surface calcium ions, followed by hydrogen-bonded interactions to surface oxygen ions and, to a much lesser extent, surface fluorides. Bridging between two surface calcium ions is the preferred mode of adsorption, when the geometry of the adsorbates allows it, and multiple interactions between surfaces and adsorbate molecules lead to the largest adsorption energies. All adsorbates containing carbonyl and hydroxy groups interact strongly with the surfaces, releasing energies between approximately 100 and 215 kJ mol−1, but methylamine containing only the –NH2 functional group adsorbs to the surfaces to a much lesser extent (25–95 kJ mol−1). Both hydroxy methanamide and hydroxy ethanal prefer to adsorb to some surfaces in an eclipsed conformation, which is a requisite for these functional groups. Sorption of the organic material by replacement of pre-adsorbed water at different surface features is calculated to be mainly exothermic for methanoic acid, hydroxy methanamide and hydroxy ethanal molecules, whereas methyl amine would not replace pre-adsorbed water at the fluorapatite surfaces. The efficacy of the surfactant molecules is calculated to be hydroxy aldehydes > alkyl hydroxamates > carboxylic acids ≫ alkyl amines. The results from this study suggest that computer simulations may provide a route to the identification or even design of particular organic surfactants for use in mineral separation by flotation. 相似文献
2.
Time-of-flight laser-ionization mass spectrometry was applied to study the chemical composition of mineral particle surfaces
in a sulphide-rich mine-tailings impoundment. This surface-sensitive technique provides chemical information from surfaces
of irregularly shaped mineral particles (both conductive and insulators) less than 100 μm in diameter, which are considered
to be representative of particle surface coatings in the tailings pile (after drying). In addition, depth profiles in the
mineral particles were obtained. The combination of speed of analysis (1 min), small beam-diameter (2–4 μm), surface sensitivity
(2–10 nm), trace-element sensitivity, and capability to analyze rough surfaces makes this method useful as a complement to
studies of pore-water geochemistry and tailings mineralogy. As an example, the behavior of Pb and As in the Kidd Creek tailings
dam near Timmins, Ontario, Canada, was studied, using a combination of surface analyses, and pore-water geochemical data.
Received: 22 February 1995 / Accepted: 6 January 1996 相似文献
3.
L. Borgnino M. G. Garcia M. V. del Hidalgo M. Avena C. P. De Pauli M. A. Blesa P. J. Depetris 《Aquatic Geochemistry》2010,16(2):279-291
We propose a model that explains the acid–base surface properties of clastic sediments from two Argentinean reservoir lakes.
The model uses potentiometric titration data sets and fixed parameters such as the apparent stability constants and reaction
stoichiometries of acid–base equilibriums involving known mineral phases. The model considers that sediments act as a set
of independent sorption surfaces, such as organic matter, clay silicate, and iron (hydr)oxides, thus the acid–base equilibrium
and the correspondent protolytic constants are represented by a humic acid, a Na-illite, and a poor crystalline Fe-hydr(oxide).
In agreement with experimental data, the model predicts that all sediment samples show a similar charging behavior, increasing
the negative charge as the pH increases. The net charge of sediments is controlled by the presence of negatively charged minerals
and/or organic matter coatings. This reveals the great influence of clays and organic matter functional groups on the acid–base
surface properties of sediments, and consequently on the surface reactivity toward contaminant transport. 相似文献
4.
5.
设计了在接近实际储层温压条件下,流体介质为纯原油时在冰洲石中合成烃类包裹体的实验。合成样品的显微观察及荧光分析证实实验成功合成了烃类包裹体,实验证明油气对晶体生长和包裹体的形成有抑制作用,但不会终止其形成,纯油条件晶体仍能生长捕获包裹体,水并不是矿物生长捕获烃类包裹体的必须条件。结合矿物润湿性实验及前人研究将碳酸盐岩烃类包裹体捕获机制归纳为3种情况:油水共存(水润湿)、油水共存(油润湿)及纯油条件。水润湿条件下由水溶液提供矿物质来源,较易形成包裹体; 油润湿条件下由水溶液和油中的极性组分共同提供矿物质来源; 纯油条件下由原油中的极性组分和裂解产生的有机酸提供物源,形成烃类包裹体较少,晶体生长受到抑制。 相似文献
6.
采用测量水中油滴在矿物表面接触角的方法,利用接触角测量仪测量了不同矿化度水中,不同单组分油和混合组分油在不同矿物表面的接触角,提出了一套合理的测量方法,保证了测量结果的准确性。经过测量润湿角的大小,对比发现水中矿物的亲油性由强到弱依次为：云母＞黄铁矿＞方解石＞白云石＞石英。矿物类型、油组分类型和水的矿化度都对接触角有较大影响：不同的矿物表面油水的润湿性不同;随着油滴中正十八烷含量的增多,油滴在云母表面的接触角变小,润湿性变好,在其它矿物表面的润湿性略有不同;随着水矿化度的提高,油滴在云母表面的接触角呈现出明显变大的趋势,润湿性逐渐变差,在其它矿物表面的润湿性略有不同。 相似文献
7.
Miroslav Boboň Alfred A. Christy Daniel Kluvanec L’udmila Illášová 《Physics and Chemistry of Minerals》2011,38(10):809-818
Recently, near infrared spectroscopy in combination with double derivative technique has been effectively used by Christy
(Vib Spectrosc 54:42–49, 2010) to study and differentiate between free and hydrogen bonded silanol groups on silica gel surface. The method has given some
insight into the type of functionalities, their location in silica gel samples, and the way the water molecules bind onto
the silanol groups. The important information in this respect comes from the overtones of the OH groups of water molecules
hydrogen-bonded to free silanol groups, and hydrogen-bonded silanol groups absorbing in the region 5,500–5,100 cm−1. Chemically, opal minerals are hydrated silica and the same approach was adapted to study the state of water molecules, silanol
functionalities, and their locations in opal samples from Slovakia. Twenty opal samples classified into CT and A classes and
one quartz sample were used in this work. The samples were crushed using a hydraulic press and powderized. Each sample was
then subjected to evacuation process to remove surface-adsorbed water at 200°C, and the near infrared spectrum of each sample
was measured using a Perkin Elmer NTS FT-NIR spectrometer equipped with a transflectance accessory and a DTGS detector. The
samples were also heated to 750°C to remove the hydrogen-bonded silanol groups on the surface to reveal their locality. Second
derivative profiles of the near infrared reflectance spectra were obtained using the instrument’s software and used in the
detailed analysis of the samples. The analysis of the near infrared spectra and their second derivative profiles had the aim
in finding relationships between the surface chemical structure and the classification of opal samples. The dry opal samples
were also tested for their surface adsorption effectivity toward water molecules. The results indicate that the opal samples
contain (1) surface-adsorbed water, (2) free and hydrogen-bonded silanol groups on the surface, (3) trapped water molecules
in the bulk, and (4) free and hydrogen-bonded silanol groups in the cavity surfaces in the bulk. A part of the water molecules
in the bulk of opal minerals are found as free molecules and the rest are found in hydrogen-bonded state to either free or
vicinal or geminal silanol groups. 相似文献
8.
Vassilis Karakitsios Harilaos Tsikos Yvonne van Breugel Lyda Koletti Jaap S. Sinninghe Damsté Hugh C. Jenkyns 《International Journal of Earth Sciences》2007,96(2):343-352
Integrated biostratigraphic (planktonic foraminifera, calcareous nannofossils), chemostratigraphic (bulk C and O isotopes)
and compound-specific organic geochemical studies of a mid-Cretaceous pelagic carbonate—black shale succession of the Ionian
Zone (western Greece), provide the first evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event)
in mainland Greece. The event is manifested by the occurrence of a relatively thin (35 cm), yet exceptionally organic carbon-rich
(44.5 wt% TOC), carbonate-free black shale, near the Cenomanian–Turonian boundary within the Vigla limestone formation (Berriasian–Turonian).
Compared to the ‘Bonarelli’ black-shale interval from the type locality of OAE2 in Marche–Umbria, Italy, this black shale
exhibits greatly reduced stratigraphic thickness, coupled with a considerable relative enrichment in TOC. Isotopically, enriched
δ13C values for both bulk organic matter (−22.2‰) and specific organic compounds are up to 5‰ higher than those of underlying
organic-rich strata of the Aptian-lower Albian Vigla Shale member, and thus compare very well with similar values of Cenomanian–Turonian
black shale occurrences elsewhere. The relative predominance of bacterial hopanoids in the saturated, apolar lipid fraction
of the OAE2 black shale of the Ionian Zone supports recent findings suggesting the abundance of N2-fixing cyanobacteria in Cretaceous oceans during the Cenomanian–Turonian and early Aptian oceanic anoxic events. 相似文献
9.
Computer animation of center of mass coordinates obtained from 800 ps molecular dynamics simulations of Cs-smectite hydrates (1/3 and 2/3 water monolayers) provided information concerning the structure and dynamics of the interlayer region that could not be obtained through traditional simulation analysis methods. Cs+ formed inner sphere complexes with the mineral surface, and could be seen to jump from one attracting location near a layer charge site to the next, while water molecules were observed to migrate from the hydration shell of one ion to that of another. Neighboring ions maintained a partial hydration shell by sharing water molecules, such that a single water molecule hydrated two ions simultaneously for hundreds of picoseconds. Cs-montmorillonite hydrates featured the largest extent of this sharing interaction, because interlayer ions were able to inhabit positions near surface cavities as well as at their edges, close to oxygen triads. The greater positional freedom of Cs+ within the montmorillonite interlayer, a result of structural hydroxyl orientation and low tetrahedral charge, promoted the optimization of distances between cations and water molecules required for water sharing. Preference of Cs+ for locations near oxygen triads was observed within interlayer beidellite and hectorite. Water molecules also could be seen to interact directly with the mineral surface, entering its surface cavities to approach attracting charge sites and structural hydroxyls. With increasing water content, water molecules exhibited increased frequency and duration of both cavity habitation and water sharing interactions. Competition between Cs+ and water molecules for surface sites was evident. These important cooperative and competitive features of interlayer molecular behavior were uniquely revealed by animation of an otherwise highly complex simulation output. 相似文献
10.
Hydrated mineral surfaces play an important role in many processes in biological, geological, and industrial applications. An energy force field was developed for molecular mechanics and molecular dynamics simulations of hydrated carbonate minerals and was applied to investigate the behavior of water on the calcite surface. The force field is a significant development for large-scale molecular simulations of these systems, and provides good agreement with experimental and previous modeling results. Simulations indicate that water molecules are significantly ordered near the calcite surface. The predominant surface configuration (75-80%) results from coordination of a water molecule with a single calcium cation-carbonate anion pair, while the less common situation involves water coordination with two ion pairs. Surface restructuring and variation in coordination in the water layers results in distinct distances for water oxygens above the calcite surface—a two-component first monolayer (2.3 and 3.0 Å) and a secondary monolayer (5.0 Å). The different coordinations also alter lateral displacement, hydrogen bonding, and surface-normal orientation of the water molecules. The ordering of water molecules and the formation of a unique hydrogen bonding network at the calcite surface influence the physical properties of the interfacial water. Surface exchange of water molecules is observed by molecular dynamics simulation to occur at a rate of one exchange per 10 ps. Diffusion coefficients derived from mean square displacement analysis of atomic trajectories indicate a dependence of water transport based on the distance of the water molecules from the calcite surface. 相似文献
11.
Possible types of anion-cation packing of mineral surface were evaluated. Their role was estimated for the decoration of minerals
with gold under vacuum (process simulating crystallization on a surface), mineral growth and intergrowth, adsorption, surface
diffusion, and other surface processes. It was shown that there are two distinct types (I and II) of mineral surfaces differing
in the character of crystallization of gold nanoparticles during decoration. Type I includes surfaces showing predominant
formation of gold nanoparticles (5–15 nm) on growth (dissolution, evaporation) steps, dislocations, and point defects. These
surfaces are represented by packed layers of O−2 anions, alternating anions and cations, and identical atoms. Type II includes surfaces with the statistical distribution
(109–12 cm−2) of gold nanoparticles (5–30 nm). Such patterns are characteristic of surfaces with packing of OH− groups, OH− in combination with O−2, and with the statistical distribution of anions and cations. Type I surfaces show low adsorption capacity and a large extent
of diffusion on them (∼103–4 nm). In contrast, type II surfaces have high adsorption capacity and low (∼50 nm) surface diffusion. Minerals dominated by
type I surfaces grow by the layer and spiral mechanisms, and those dominated by type II surfaces grow by the normal mechanism.
Original Russian Text ? N.D. Samotoin, L.O. Magazina, 2006, published in Geokhimiya, 2006, No. 10, pp. 1068–1084. 相似文献
12.
Water structure at hematite-water interfaces 总被引：1，自引：0，他引：1
Sebastien Kerisit 《Geochimica et cosmochimica acta》2011,75(8):2043-17045
The atomic-level structure of water at mineral surfaces is an important controlling factor in interfacial reactions such as foreign ion incorporation, crystal growth and dissolution, and redox reactions. Molecular dynamics simulations with four different models based on interatomic potentials have been carried out to determine the atomic-level structure of three hematite-water interfaces. In addition, for each of the three surfaces, different terminations or protonation schemes were considered. The availability of surface X-ray scattering data for the surfaces considered here allowed for an extensive comparison with experimental data. Qualitatively, with the exception of one termination with one model, all models predict the correct arrangement of water molecules at the interface. Quantitatively, the agreement with experimental positions, distances, and layer occupancies is good to excellent, especially given the range of values reported in published experimental studies. Therefore, this study provides further evidence that interatomic potential models can be used to reliably predict the structure of mineral-water interfaces. In addition, molecular simulations are a valuable source of information to complement surface X-ray scattering experiments owing to their ability to directly determine the position of hydrogen atoms and to yield three-dimensional predicted structures at no added cost, as demonstrated in this work. Indeed, the molecular dynamics trajectories were analyzed to determine the surface structural controls on the interfacial water structure. Each of the three surface functional groups present at the surfaces considered in this work, namely, triply-coordinated oxo, doubly-coordinated hydroxo, and singly-coordinated aquo groups, was found to form similar hydrogen bond configurations with adsorbed water molecules at all surfaces. Oxo groups accept long-lasting and linear hydrogen bonds from adsorbed water molecules; hydroxo groups can form hydrogen bonds with other surface functional groups as well as with adsorbed water molecules; and aquo groups normally only donate hydrogen bonds to other surface groups or adsorbed water molecules. Additionally, the majority of adsorbed water molecules were found to adopt multiple configurations and orientations. This information was used to evaluate three-dimensional structural models of the interfaces, which were previously derived experimentally from one-dimensional electron density profiles and steric considerations. 相似文献
13.
Adsorption of polar aromatic hydrocarbons on synthetic calcite 总被引：1，自引：0，他引：1
Lene Madsen Laila Grahl-Madsen Christian Grøn Ida Lind John Engell 《Organic Geochemistry》1996,24(12):1151-1155
The wettability of hydrocarbon reservoirs depends on how and to what extent the organic compounds are adsorbed onto the surfaces of calcite, quartz and clay. A model system of synthetic calcite, cyclohexane and the three probe molecules: benzoic acid, benzyl alcohol and benzylamine, have been studied by adsorption experiments. The results clearly demonstrate the differences in the adsorption behaviour between probes with different functional groups of varying polarity and acidity. The maximum adsorption decreases in the order: benzoic acid, benzyl alcohol and benzylamine. The order of magnitude of ΔG° for the adsorption process implies the formation of a strong bond between the calcite surface and the adsorbate molecules. 相似文献
14.
Release of CO2 from surface ocean water owing to precipitation of CaCO3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface
water to sedimentary storage was studied by means of a quotient θ = (CO2 flux to the atmosphere)/(CaCO3 precipitated). θ depends not only on water temperature and atmospheric CO2 concentration but also on the CaCO3 and organic carbon masses formed. In CO2 generation by CaCO3 precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric
CO2 concentration (195–375 ppmv), and increasing CaCO3 precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic
carbon counteracts the CO2 production by carbonate precipitation and it results in lower CO2 emissions from the surface layer. When atmospheric CO2 increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO2 transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric
CO2. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon
from land, the calculated CO2 flux to the atmosphere is a function of the CaCO3 and Corg net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO2 flux near the Last Glacial Maximum is 17 to 7×1012 mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time
it is 38–42×1012 mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic
emissions of CO2 to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total
alkalinity owing to the CaCO3 storage and consequent emission of CO2. These results are in agreement with the conclusions of a number of other investigators. As the CO2 uptake in mineral weathering is a major flux in the global carbon cycle, the CO2 weathering pathway that originates in the CO2 produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large
imbalances of the atmosphere and land organic reservoir at 102–104-year time scales. 相似文献
15.
N. Mukaratirwa-Muchanyereyi J. Kugara M. F. Zaranyika 《International Journal of Environmental Science and Technology》2016,13(8):1941-1950
The adsorbent properties of dried water hyacinth root biomass towards four polar solvents (dichloromethane, ethyl acetate, diethyl ether and acetone) were studied by inverse gas chromatography between 40 and 70 °C. The enthalpy of adsorption values obtained for the adsorption of the four solvents on untreated root biomass range from ?51.234 kJ mol?1 for acetone, an amphoteric solvent, to ?74.658 kJ mol?1 for dichloromethane, an acidic solvent. Mineral acid and organic solvent treatment led to reduction in the values of the enthalpy of adsorption for all four solvents. The Lewis acidity parameters calculated from the enthalpy of adsorption values were 0.408, 0.267 and 0.356, while the corresponding Lewis basicity parameters were 3.76, 1.80 and 2.34, respectively, for untreated, mineral acid-treated and organic solvent-treated water hyacinth root biomass. The Lewis basicity parameter-to-Lewis acidity parameter ratios for the untreated, acid-treated and organic solvent-treated biomass were found to be 9.22, 6.74 and 6.57, respectively, indicating (a) that all the surfaces of the untreated, mineral acid-treated and organic solvent-treated water hyacinth root biomass are basic in nature and (b) that for all volatile polar solvents studied, the adsorption interaction involves the lowest unoccupied molecular orbital of the solvent as the electron acceptor and the highest occupied molecular orbital of the water hyacinth root biomass surface adsorbent site as the electron donor. 相似文献
16.
Chlorinated volatile organic compounds found near the water surface of heavily polluted rivers 总被引：4，自引：4，他引：0
D. F. Juang Ph.D. C. H. Lee Ph.D. S. C. Hsueh M.Sc. 《International Journal of Environmental Science and Technology》2009,6(4):545-556
The objectives of this study were to identify the chlorinated volatile organic compounds near the water surface of two heavily polluted rivers in the south of Taiwan and compare their concentration distributions. Air samples were collected seasonally at the upstream, midstream and downstream water surfaces of each river and the chlorinated volatile organic compounds were analyzed qualitatively and quantitatively by gas chromatography and electron capture detector. Totally, twelve kinds of chlorinated volatile organic compounds were found at the water surfaces of both rivers and many of them were reported to be carcinogenic or probably carcinogenic to human. The results showed that each chlorinated volatile organic compound had its own distribution pattern and no good correlation of chlorinated volatile organic compounds between both rivers was obtained. The chlorinated volatile organic compounds identified at the river water surface of Fong Shan Stream showed much higher concentration than those of Chuen-Tsen River. Several chlorinated volatile organic compounds, including chlorodibromomethane, hexachlorobutadiene, 1,1,2,2-tetrachloroethene and 1,2-dibromo-3-chloropropane were found with much higher concentration (mean concentrations of 124.5 μg/m3, 334.5 μg/m3, 92.2 μg/m3, 268.4 μg/m3, respectively) at the water surface of Fong Shan Stream in some seasons (especially spring and summer, summer and winter, spring and winter, spring and summer, respectively) and they were reported to be possibly carcinogenic to human. Therefore, it may be concluded that the people living close to Fong Shan Stream possibly had higher health risks due to the release of volatile organic compounds from the heavily polluted river. 相似文献
17.
macroscale processes that perturb general groundwater chemistry and therefore mineral–water equilibria; and microscale interactions, where attached organisms locally perturb mineral–water equilibria, potentially releasing limiting trace nutrients
from the dissolving mineral.
In the contaminated unconfined glacio-fluvial aquifer near Bemidji, Minnesota, USA, carbonate chemistry is influenced primarily
at the macroscale. Under oxic conditions, respiration by native aerobic heterotrophs produces excess carbon dioxide that promotes
calcite and dolomite dissolution. Aerobic microorganisms do not colonize dolomite surfaces and few occur on calcite. Within
the anoxic groundwater, calcite overgrowths form on uncolonized calcite cleavage surfaces, possibly due to the consumption
of acidity by dissimilatory iron-reducing bacteria. As molecular oxygen concentration increases downgradient of the oil pool,
aerobes again dominate and residual hydrocarbons and ferrous iron are oxidized, resulting in macroscale carbonate-mineral
dissolution and iron precipitation.
Feldspars, in contrast, weather exclusively at the microscale near attached microorganisms, principally in the anoxic region
of the plume. Native organisms preferentially colonize feldspars that contain trace phosphorus as apatite inclusions, apparently
as a consequence of the low P concentration in the groundwater. These feldspars weather rapidly, whereas nearby feldspars
without trace P are uncolonized and unweathered. Feldspar dissolution is accompanied by the precipitation of secondary minerals,
sometimes on the bacterial cell wall itself.
These observations suggest a tightly linked biogeochemical system whereby microbial processes control mineral diagenesis at
many scales of interaction, and the mineralogy and mineral chemistry influence microbial ecology. Only the macroscale interaction,
however, is easily observable by standard geochemical methods, and documentation of the microscale interactions requires microscopic
examination of microorganisms on mineral surfaces and the locally intense diagenetic reactions that result.
Received, May 1999/Revised, October 1999/Accepted, October 1999 相似文献
18.
A three-dimensional, finite-element flow model was used to assess the hydrogeological effects of depressurizing coalbeds
lying in the Weary Creek exploration block, Elk River valley, southeastern British Columbia, Canada. The simulation results
permit, at an early stage, assessment of the environmental and economic implications of how the flow system may respond to
depressurization.
Estimated reservoir conditions for the coal-seam gas targets lying within the Upper Jurassic–Lower Cretaceous Mist Mountain
Formation indicate that the coalbeds must be depressurized by up to 350 m to attain the critical gas desorption pressure.
The simulations suggest that depressurizing has little effect on groundwater flux to the Elk River. Simulated water production
for three depressurizing wells operating under steady-state, single-phase flow for initial reservoir conditions of 13 and
16.5 cm3/g is 645 m3/d (4,057 barrels/d) and 355 m3/d (2,233 barrels/d), respectively.
Groundwaters collected from monitoring wells have relatively low salinity, ranging from about 250–1,300 mg/L. The groundwater
is supersaturated with respect to Ca–Mg–Fe carbonates (calcite, dolomite, and siderite) and Al-bearing silicates, including
kaolinite and illite. Dissolved trace-metal concentrations are low; only Fe, Cd, Cr, and Zn exceed Canadian water-quality
guidelines for aquatic life. Groundwaters were devoid of the more soluble monocyclic aromatic organic compounds, including
benzene, toluene, ethylbenzene, and polycyclic aromatic compounds, including naphthalene.
Electronic Publication 相似文献
19.
《Geochimica et cosmochimica acta》1999,63(19-20):3145-3152
The adsorption of organic molecules at mineral–fluid interfaces has a profound influence upon geochemical reaction and transport processes, yet little is known about the in situ structures or properties of organic layers at mineral–fluid interfaces. We describe an X-ray reflectivity study of stearate monolayers adsorbed at the calcite surface from methanolic solutions. Using these measurements we are able to determine important aspects of the in situ structure, bonding, adsorption, and growth mechanisms of stearate monolayers. The experimental approach demonstrated here can be applied widely in studying the interaction of organic molecules with mineral surfaces in aqueous systems. 相似文献
20.
Heavy rainfalls, between 25 and 100 mm·h–1, were simulated on Pliocene/Quaternary sediments. To reproduce the heterogeneity
of natural environments, 231 small plots of various sizes (between 2.5 and 3.5 m2; mean: about 3 m2) were used. The duration of all simulations was 1 h. We used water that had been collected during natural rainfall. The concentration
of clay particles in the sheet wash depended upon the concentration of dissolved sodium in the wash (for about 42%) and of
the sheet wash quantity (for about 37%). Under natural water conditions colloidal matter, like clay minerals, is charged negatively
and therefore is destabilized by metal cations such as in the case of Na+. Results suggest that relatively higher concentrations of montmorrillonite were related to higher concentrations of sodium
as opposed to illite and kaolinite. Microflakes of up to 25 μ were observed to vary between face-to-edge and face-to-face
modes (competition between protons and other cations). The concentration of dissolved sodium (Na+) in the runoff water depends on water and sodium balances such as atmospheric input, infiltration, evaporation and surface
water runoff. The reduction of vegetation cover increases the amount of salt and amorphous matter in/on the topsoil between
heavy rainfall generations. The best predictor to explain montmorillonite, illite and kaolinite in % of mineral clay-sized
matter in the surface water runoff (sheet wash) is the percentage of each clay mineral in the topsoil. As opposed to illite
and kaolinite, more sheet wash indicate for montmorillonite relatively higher concentrations in the wash. The results of model
simulations were confirmed on different field plots of about 1 ha and small catchments during natural heavy rainfall events.
Models can also be used to understand and to better simulate sheet, rill and gully erosion, micropedimentation; and pedimentation. 相似文献