Surface Sorption Processes Research Articles

Evolution of gas transport pattern with the variation of coal particle size: Kinetic model and experiments

Gas desorption laws varies with coal particle size. Their proper description is of great importance to natural gas engineering. This paper tries to summarize the internal links in commonly used models and combine them into a more general form. The combined general model is capable of describing fracture flow, matrix diffusion and surface sorption processes in pores with shapes like flat plates, cylinders and spheres. It can also be simplified into a power function which can be readily implemented into simulation of sorption and calculation of dynamic Fickian diffusion coefficients. Experiments including low-temperature liquid N2 adsorption, proximate analysis, isothermal methane sorption and desorption experiments with different particle sizes were conducted to validate the model. Other sorption data from literature were also collected for validation. The fitting results can help explain the size dependence of desorption characteristics and show the flow type evolutions during the damage of pore system.

Dissolution and Sorption Processes on the Surface of Calcite in the Presence of High Co2+ Concentration

The interaction of the calcite surface with Co2+-rich aqueous solutions ([Co2+aq]initial = 1000 ppm, i.e., ca. 17 mM) was investigated by means of macroscopic experiments and surface spectroscopic techniques. In the case of the macroscopic experiments, calcite powder and monocrystals were immersed into solutions for different time periods (from 1 min to one month). The Ca concentrations in the filtrates was measured by means of atomic absorption spectrometry (AAS) while the interacted solids were studied using a combination of X-ray photoelectron spectroscopy (XPS) and 12C-rutherford backscattering spectrometry (12C-RBS). The macroscopic data showed a characteristic surface dissolution process, in parallel to the surface sorption processes. Adsorption and co-precipitation were seen for almost the entire immersion period for both calcite powder and monocrystals. The surface study by XPS (analyzed at a depth of approximately 12 nm) suggested that adsorption takes place in the first hour of the interaction, followed by incorporation of Co2+ into calcite surface layers, leading to the formation of a Co2+-bearing surface (co)precipitate, which occurs over a period of hours and days. The 12C-RBS measurements on calcite { 10 1 ¯ 4 } indicated that the thickness of this surface co-precipitate was 270 nm after one day and then stabilized at 320 nm after more than a week.

Arsenic solid-phase speciation and reversible binding in long-term contaminated soils

Historic arsenic contamination of soils occurs throughout the world from mining, industrial and agricultural activities. In Australia, the control of cattle ticks using arsenicals from the late 19th to mid 20th century has led to some 1600 contaminated sites in northern New South Wales. The effect of aging in As-mobility in two dip-site soil types, ferralitic and sandy soils, are investigated utilizing isotopic exchange techniques, and synchrotron X-ray adsorption spectroscopy (XAS). Findings show that historic soil arsenic is highly bound to the soils with >90% irreversibly bound. However, freshly added As (either added to historically loaded soils or pristine soils) has a significantly higher degree of As-accessibility. XAS data indicates that historic soil arsenic is dominated as Ca- (svenekite, & weilite), Al-(mansfieldite), and Fe- (scorodite) like mineral precipitates, whereas freshly added As is dominated by mineral adsorption surfaces, particularly the iron oxy-hydroxides (goethite and hematite), but also gibbsite and kaolin surfaces. SEM data further confirmed the presence of scorodite and mansfieldite formation in the historic contaminated soils. These data suggest that aging of historic soil-As has allowed neoformational mineral recrystallisation from surface sorption processes, which greatly reduces As-mobility and accessibility.

Evaluation of Surface Sorption Processes Using Spectral Induced Polarization and a (22)Na Tracer.

We investigate mechanisms controlling the complex electrical conductivity of a porous media using noninvasive spectral induced polarization (SIP) measurements of a silica gel during a pH dependent surface adsorption experiment. Sorption of sodium on silica gel surfaces was monitored as the pH of a column was equilibrated at 5.0 and then successively raised to 6.5 and 8.0, but the composition of the 0.01 M NaCl solution was otherwise unchanged. SIP measurements show an increase in the imaginary conductivity of the sample (17.82 ± 0.07 μS/cm) in response to the pH change, interpreted as deprotonation of silanol groups on the silica gel surface followed by sorption of sodium cations. Independent measurements of Na(+) accumulation on grain surfaces performed using a radioactive (22)Na tracer support the interpretation of pH-dependent sorption as a dominant process controlling the electrical properties of the silica gel (R(2) = 0.99) and confirms the importance of grain polarization (versus membrane polarization) in influencing SIP measurements of silicate minerals. The number of surface sorption sites estimated by fitting a mechanistic, triple-layer model for the complex conductivity to the SIP data (13.22 × 10(16) sites/m(2)) was 2.8 times larger than that estimated directly by a (22)Na mass balance (5.13 × 10(16) sites/m(2)), suggesting additional contributions to polarization exist.

Interaction of [formula omitted] with CHA-type zeolitic materials

The interaction of acidic (pHin 3 and 4) aqueous uranium solutions with an Italian chabazite-rich tuff (Vesuvio area) and pure Ca-chabazite crystals from Isle of Skye (Scotland) in raw and Na form were investigated in the presence of background electrolyte (0.1M NaNO3) under ambient conditions using a batch equilibrium technique. The maximum uranium uptake by the chabazitic-tuff, its Na form and the pure chabazite crystals from Isle of Skye was found to be ca. 23mg/g whereas the Na form of the pure chabazite crystals showed higher uptake ability (ca. 34mg/g). The experimental data have been analyzed using the Langmuir, Freundlich, Redlich–Peterson, Sips, Toth and Dubinin–Radushkevich models. The surface heterogeneity, as well as the chemical nature and behavior of uranium species produced deviations far too complicated to be mathematically described by simple empirical model. Additionally, difficulties in attaining global convergence were encountered when using the three-parameter models due to the substantial sensitivity to initial parameter guesses. According to microscopic measurements and literature data related to the structure of CHA-type zeolites, the uranium uptake took place mainly through surface sorption processes (adsorption and surface precipitation).

Water quality of the Guadiamar River after the Aznalcóllar spill (SW Spain)

In April 1998, a spill of 6 hm 3 of pyritic mud and acidic water was released into the Guadiamar River due to the rupture of the Aznalcóllar tailings dam. Before the spill, the river was already strongly affected by acid mine drainage (AMD). In this study, the water quality of the Guadiamar River is analysed from a periodic sampling started after the spill. Previous data of the water quality have also been obtained. A recovery of the water quality is observed from 2002 on. The distribution of arsenic is opposed to that of the rest of metals, with the lowest concentrations to the north, due to the adsorption and/or coprecipitation on ferric oxyhydroxides. In the southern area, when pH values are close to 8, arsenic desorption occurs. There is a seasonal pattern of the trace metal content evolution, different in the northern and southern zones of the river. In the northern area the highest polluting levels occur in summer, due to a lower dilution of the mining leachates. In the southern area, the highest metal levels occur during the winter, since during the summer metals remain held by surface sorption processes in the hyporheic zone of the river.

Sorption of Am(III) and Eu(III) onto γ-alumina: experiment and modelling

The present paper describes the surface complexation behaviour of trivalent metal ions, Am(III) and Eu(III), on well characterised γ-alumina. Experiments are conducted at different pH (4-8) and ionic strength (0.001 - 0.1 M NaClO4) either in the presence or absence of CO2. By varying the metal ion concentration from 10-9to 10-4mol/L, the sorption isotherm is established under each given experimental condition. Different surface complexation models are applied to the experimental results to interpret and appraise the surface sorption processes under different experimental conditions. A comparison of the present results is made with the Eu(III) sorption onto the hematite mineral surface investigated previously. It has been shown that sorption properties of hematite and γ-alumina seem to be quite similar. For both systems, a good agreement is found between experimental data and modelling, once using the two site surface complexation model and the same complexation constants for the respective monodentate surface complex. The Eu(III) sorption reaction is additionally studied in-situ by time resolved laser fluorescence spectroscopy (TRLFS). Formation of inner-sphere complexes can be deduced from the emission spectra. The continuous increase of the fluorescence life time with increasing pH starting from pH = 5.0 indicates that surface complexation is accompanied by a decreasing number of hydration water in the first coordination sphere.

Foreign elements in a clam shell: a clue to the history of marine pollution events

A new phenomenon of distribution of foreign elements in clam shells (maximum quantity at surface and along edges of the shell) is reported and interpreted. The new finding makes it possible to reconstruct the history of contamination in the waters surrounding the organism concerned. It further suggests inadequacy of previous techniques in using mollusk shells for measuring the degree of water pollution. Bivalve shells have been shown to be useful in monitoring heavy-metal pollution in the marine environment; shell composition changes as a result of changing water chemistry (Bertine and Goldberg, 1972; Goldberg et al., 1978; Miramand et al., 1980). Apparently, shells provide more sensitive and more irreversible clues for monitoring changes in ambient heavy metals than the soft tissues (Miramand et al., 1980; Koide et al., 1982). We report here on the composition of metals and sulfur in the shell, and illustrate the usefulness of shell chemistry as a tool for deterrnining the history of the chemical environment of the organism concerned. Individuals of the clams Meretrix lusoria (Roding) were collected from a shallow-water culture farm near an estuary in southern Taiwan (120°E, 23N). This species inhabits sandy beaches exposed to air for a few hours during low tide. These clams are found in an anoxic environment with gray-to-black organic matter. Shell samples were first separated from living soft tissues, washed with distilled water, exposed to ultrasonic radiation for 2 h to remove possible foreign materials, and then air-dried prior to scanning electron microscopy (SEM). Shells of 3 to 4 cm in width which represent 8 mo to 1 yr of growth were used. Point-count analyses by SEM (JSM 35-CF), operating at 15 to 25 KV, coupled with energy dispersive analysis of X-ray (EDAX) technique, were made on the Q Inter-Research/Printed in F. R. Germany outer surface, as well as on intermediate and inner layers exposed in the fractured clam shell. Sample size was estimated to be several microns. Occasionally, an electron beam was scanned on a specific area (e.g. 3 X 3 pm) in order to control the measurements. The distance from hinge to the measuring spot was estimated on the magnified electron image of the shell. In the inner and intermediate layers only Ca was detected, X-ray diffraction (CuK,) analysis indicated aragonite to be the major substance in the intermediate layer. Significant amounts of Ca, S and Fe, with minute amounts of Cu, Zn, C1 were detected in the outer layer (periostracum). The significant amounts of Fe and S on the shell are expected since the habitat of the clam, similar to other subtidal anoxic marine sediments, contains abundant amounts of soluble sulfide (H,S and HS-) and acid-labile sulfides (FeS) (Howarth and Giblin, 1983). Ca. S, Fe, Cu and Zn were analyzed next from the umbo to the posterior edge of the shell (following the growth direction), and the relative amounts of S, Fe, Cu, and Zn over Ca were estimated from the EDAX peak height (i.e. counts). Ca was used as reference because it is the major constitutional element of the shell. Fig. 1 and 2 show a general trend of increasing S, Fe, Cu and Zn towards the outer edge (younger portion) of the shell. This is in contrast to the previous concept, i.e. that pollutants accumulate with increasing age, which implies that the older portion should be richer in metals than the younger portion of the shell. Surface sorption processes are assumed to be responsible for the accumulation of metal pollutants in the shell (Miramand et al., 1980). Such assumption cannot be used to explain our data either. If surface sorption processes were the main operating mechanisms, we should expect a uniform distribution of for188 Mar. Ecol. Prog. Ser 18: 187-189, 1984

Vanadium transfer in the mussel Mytilus galloprovincialis

Radiotracers were used to study processes controlling the accumulation and elimination of vanadium in the Mediterranean mussel Mytilus galloprovincialis. Vanadium uptake rates varied inversely with both salinity and vanadium concentration in water, but were independent of temperature. After a 3 wk exposure to 48V, the highest concentration factors were found in the byssus (≈1900) with much lower values computed for shell (≈ 70) and soft tissues (≈5). More than 90% of the total 48V accumulated was fixed to shell, suggesting that uptake is primarily a result of surface sorption processes. Much of the vanadium in shell was firmly bound to the periostracum and was not easily removed by acid leaching. Food-chain experiments indicated that the assimilation coefficient for ingested vanadium is low (≈7%) and that the assimilated fraction is rapidly excreted from the mussel. These findings coupled with knowledge of in situ and experimentally-derived vanadium concentration-factors have allowed a preliminary assessment of the relative importance of the food and water pathways in the contamination of mussels under conditions of acute and chronic exposure. Contaminated mussels transferred to clean sea water lost 48V at rates that depended upon temperature but were largely unaffected by either salinity or by vanadium levels in mussel tissues. Total vanadium depuration was slow and was governed by loss from a slowly-exchanging compartment with a characteristic half-time of about 100 d. Individual mussel tissues were analyzed for stable vanadium and the possibility of using these tissues, particularly the byssus, as bioindicators of ambient vanadium levels in the marine environment is also discussed.

Differential sorption of organic matter by various sized sediment particles in recent sediment from the bering sea

A recent unconsolidated marine sediment collected from the Aleutian basin of the Bering Sea (57‡02.9′N, 176‡57.4′W) was separated into eight size fractions by sieving. Each of the fractions was analyzed for density, organic carbon, total nitrogen and various organic materials. A detailed analysis of the correlation of organic carbon and total nitrogen to the mean diameter of the particles separated, indicated that the surface sorption processes of organic matter were the determinative factor controlling the concentration of organic carbon and total nitrogen on silt and clay particles of the sediments. Selective sorption of amino acids was found to occur in the 8–20 and 5–8Μm. fractions of the sediment. This is assumed to be due to their surface active property.

Interaction of organic compounds with calcium carbonate-II. Organo-carbonate association in Recent sediments

Surface area measurements as well as organic carbon, nitrogen and phosphorus analyses on various grain size fractions of carbonate mud samples confirm that in natural environments of carbonate deposition, surface sorption processes take place which are similar to those described earlier for dissolved organics and artificially suspended calcite particles in both seawater and synthetic solutions. The specific surface area of the sediment increases from 1.8m 2/g for the coarse-grained fraction to 12.5 m 2/g for the fine material; likewise organic carbon, nitrogen and phosphorus increase with increasing surface area so that there are 1.20 mg C, 0.175 mg N and 0.06–0.20 mg P associated with every square meter of carbonate surface irrespective of the mineralogy of the sediment particles. It appears that the organic matter in these sediments is similar in composition, structure and quantity to the organic layers produced in sorption experiments. With their apparently defined structure and ubiquitous nature, these layers could determine the mineralogy and orientation of submarine carbonate cement or could even be a prerequisite to calcification in general.