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1.
Iron oxide nanoparticles (nano-Fe) have been widely used in environmental remediation, including that of emerging contaminants, such as antibiotics. Magnetite nanoparticles (nano-Fe3O4) have been reported to form on the outer surface of nano-Fe and have the potential to be a good sorbent for certain antibiotics. This study reports, for the first time, the kinetics and thermodynamics of adsorption of a common tetracycline group antibiotic, oxytetracycline (OTC), on nano-Fe3O4. Batch sorption kinetics were evaluated by varying initial OTC concentration (0.25–2 mM), nano-Fe3O4 concentration (2.5–20 g L?1), pH (3.8–7.6), temperature (5, 15, 35 °C), and ionic strength (0.01–0.5 M KCl) to derive thermodynamic and kinetic constants. Results show that OTC sorption kinetics is rapid and increases with increasing temperature. The derived thermodynamic constants suggest a surface chemical-controlled reaction that proceeds via an associative mechanism. Results indicate the potential of developing a nano-magnetite-based remediation system for tetracycline group of antibiotics.  相似文献   

2.
Aluminium smelters are major sources of F emission to the environment. We studied, in laboratory experiments, the sorption and desorption of fluoride on organic and mineral horizons of soils located within 2 km from one of these factories, situated in the northern coast of Galicia (NW Spain). The soils, developed from granite, are acid (pH H2O 3.9–5.5), rich in organic matter (4–16 % C in the A horizon) and most A horizons have high Al saturation in the exchange complex. All samples showed a notable F sorption, between 1,066 and 1,589 mg kg?1, after adding 200 mg F L?1, which accounts for 53–80 % of F added. The sorption was slightly higher in the A horizons than in the respective organic horizons (differences of up to 194 mg kg?1). The fluoride sorption upon addition of 200 mg F L?1 correlated significantly (p < 0.05) with soil pH in water (r = ?0.77), iron extracted by acid ammonium oxalate (r = 0.68), aluminium plus iron extracted by acid ammonium oxalate (r = 0.63), exchange aluminium (r = 0.52) and clay percentage in soil (r = 0.76). The F sorption fitted to both Langmuir and Freundlich models. Desorbed F accounted for only 12–22 % of sorbed fluoride and correlated (p < 0.05) negatively with non-crystalline (extracted by acid ammonium oxalate) Fe (r = ?0.51) and clay content (r = ?0.74) and positively with organic matter (r = 0.69) and with the effective cation exchange capacity of the soil (r = 0.50).  相似文献   

3.
The objective of this work was to study sorption–desorption and/or precipitation–dissolution processes of Hg(II) compounds considering an eventual contact of soils with Hg-bearing wastes. In addition, this study contributes new data about Hg(II) chemistry in alkaline systems. Saline and alkaline soils with low organic matter (<1 %) and high clay content (60–70 %) were obtained near a chlor-alkali plant. Batch techniques were used to perform the experiments using 0.1 M NaNO3 solutions. Total Hg(II) concentrations ranged from 6.2 × 10?8 to 6.3 × 10?3 M. Sorption of Hg(II) was evaluated at two concentration ranges: (a) 6.2 × 10?8 to 1.1 × 10?4 M, and (b) 6.4 × 10?4 to 6.3 × 10?3 M. At low Hg(II) concentrations, adsorption occurred with a maximum sorption capacity ranging from 4 to 5 mmol/kg. At high Hg(II) concentrations, sorption–precipitation reactions occurred and maximum sorption capacity ranged from 17 to 31 mmol/kg. The distribution of Hg(II) hydrolysis products showed that Hg(OH)2 was the predominant species under soil conditions. According to sorption experiments, X-ray diffraction and chemical speciation modelling, the presence of Hg(OH)2 in the interlayer of the interstratified clay minerals can be proposed. Hg(OH)2 was partially desorbed by repeated equilibrations in 0.1 M NaNO3 solution. Desorption ranged from 0.1 to 0.9 mmol/kg for soils treated with 5.8 × 10?5 M Hg(II), whereas 2.1–3.8 mmol/kg was desorbed from soils treated with 6.3 × 10?3 M Hg(II). Formation of soluble Hg(II) complexes was limited by low organic matter content, whereas neutral Hg(OH)2 was retained by adsorption on clay mineral surfaces.  相似文献   

4.
This paper assesses the use of certified Iraqi montmorillonite clay as a potential sorbent for the removal of oxytetracycline (OTC) from aqueous solutions. The clay is characterized by a cation exchange capacity of 0.756 meq g?1 and a zero point charge at pH 8.7. Aqueous solutions of OTC were equilibrated with montmorillonite under various experimental conditions, such as OTC concentration, pH and clay content, for 24 h at fixed ionic strength. Two forms of montmorillonite were evaluated: regular and iron-modified form. The effect of pH was minor on OTC adsorption. Kinetic study revealed that the sorption follows a pseudo-second-order model. Sorption isotherm showed a good fit with the Freundlich model. OTC sorption onto Fe-saturated montmorillonite was analyzed statistically using a response surface design to study the effects of experimental conditions. The introduction of iron improved the adsorption characteristics of the clay due to the ability of ferric ions to make stable complexes with OTC. The most favorable operating conditions for the treatment were deemed as follows: clay content, 6.85 g L?1, oxytetracycline concentration, 1.0 mmol L?1 and pH, 5.5 for the iron-modified form.  相似文献   

5.
This study focuses on the performance of nanostructured banana peels in lanthanide-laden mine water treatment. Specifically, nanostructure formation via mechanical milling, characterization in detail and application of this sorbent media in rare earth elements (REEs) removal from synthetic and real mine water are thoroughly investigated. The sorbent samples were characterized by transmission electron microscopy, Brunauer–Emmett–Teller, X-ray diffraction and Fourier transform infrared analyses, while the amount of REEs adsorbed was analysed using inductively coupled plasma optical emission spectroscopy. Results revealed that the particle and crystallite sizes were reduced from <65,000 to <25 nm and 108 to 12 nm, respectively, as the milling progressed. Furthermore, the fracture of particles resulted in a surface area increment from 1.07 to 4.55 m2 g?1. Through Fourier transform infrared analysis, the functional groups responsible for the coordination and removal of metal ions were found to be carboxylic group (at absorption bands of 1730 cm?1) and amine groups (889 cm?1). The Langmuir maximum adsorption capacity was 47.8 mg g?1 for lanthanum and 52.6 mg g?1 for gadolinium. Meanwhile, results revealed that banana peels have a high affinity for Sm, Eu, Nd, Pr, Gd, Tb and Lu compared to other lanthanides present in the mine water samples. The results obtained so far indicate that nanostructured banana peel is a potential adsorbent for REEs removal from mine water. However, for any application, the water matrix to be treated substantially influences the choice of the sorbent material.  相似文献   

6.
Previous studies in our laboratory have demonstrated that drinking-water treatment residuals are effective sorbents of arsenic V. However, the effect of soil solution chemistry on arsenic V sorption by drinking-water treatment residuals-amended soils remains to be explored. The current study uses a batch incubation experimental set up to evaluate the effect of soil solution pH, competing ligands, and complexing metal on arsenic V sorption by a sandy soil (Immokalee series) amended with two rates (25 and 50 g kg?1) of aluminum and iron-based drinking-water treatment residuals. Experiments were conducted at three initial arsenic loads (125, 1,875, 3,750 mg kg?1) and a constant solid: solution ratio of 200 g L?1. An optimum equilibration time of 8 days, obtained from kinetic studies, was utilized for sorption experiments with both aluminum and iron drinking-water treatment residual-amended soil. Presence of phosphate decreased arsenic V sorption by both aluminum and iron drinking-water treatment residual amended soils, with a strong dependence on pH, drinking-water treatment residual types, drinking-water treatment residual application rates, and phosphate concentrations. Addition of sulfate had no effect on arsenic V sorption by aluminum or iron drinking-water treatment residual-amended soil. A complementing effect of calcium on arsenic V sorption was observed at higher pH. Results elucidating the effect of soil solution chemistry on the arsenic V sorption will be helpful in calibrating drinking-water treatment residual as a sorbent for remediation of arsenic-contaminated soils.  相似文献   

7.
A solid phase extraction method based on the immobilisation of Penicillium chrysogenum on silica was developed for preconcentration and flame atomic absorption spectrometric determination of Pb(II). The immobilised sorbent was packed in a column to optimise the conditions for its quantitative sorption and desorption. Various parameters such as pH, type of eluent, sample and eluent flow rate and influence of others ions were systematically studied. Pb(II) was quantitatively sorbed at pH 4.0 at a flow rate of 2.0 mL min?1 and eluted with 10.0 mL of 1.0 M HCl at 0.2 mL min?1 flow rate. The devised procedure applied for Pb determination in tap water, an industrial effluent and sludge sample, black tea, spinach leaves and green beans (canned food) was reproducible, with a relative standard deviation of 0.8%. The method was validated by a BCR 701 standard lake sediment sample. The limit of detection and limit of quantification for Pb(II) were 7.16 and 23.88 μg L?1, respectively, with an enrichment factor of 100.  相似文献   

8.
The goal of this study was to evaluate the soil properties and their modifications within the rhizosphere of spontaneous vegetation as key factors to assess the phytomanagement of a salt marsh polluted by mining wastes. A field survey was performed based on a plot sampling design. The results provided by the analyses of rhizospheric soil (pH, electrical conductivity (EC), organic carbon, total nitrogen, etc.) and metal(loid)s’ phytoavailability (assessed by EDTA) were discussed and related to plant metal uptake. The averages of pH and EC values of the bulk soil and rhizospheric samples were in the range of neutral to slightly alkaline (pH 7–8) to saline (>2 dS m?1), respectively. Heavy metal and As concentrations (e.g. ~600 mg kg?1 As, ~50 mg kg?1 Cd, ~11,000 mg kg?1 Pb) were higher in the rhizosphere for both total and EDTA-extractable fraction. Phragmites australis uptaked the highest concentrations in roots (e.g. ~66 mg kg?1 As, ~1,770 mg kg?1 Zn) but not in shoots, for which most of plant species showed low values for Zn (<300 mg kg?1) but not for Cd (>0.5 mg kg?1) or Pb (~20–40 mg kg?1). Vegetation distribution in the studied salt marsh looked to be more affected by salinity than by metal pollution. The free availability of water for plants and the incoming nutrient-enriched effluents which flow through the salt marsh may have hindered the metal(loid)s’ phytotoxicity. The phytomanagement of these polluted areas employing the spontaneous vegetation is a good option in order to improve the ecological indicators and to prevent the transport of pollutants to nearby areas.  相似文献   

9.
Colloidal pyrite waste rocks (CPWR) which are mainly composed of colloidal pyrite and siderite widely deposit in sulfide mines in the middle and lower reaches of the Yangtze River belt, China, especially in Tongling City, Anhui Province, China. In this paper, a fixed-bed column was used to investigate the weathering and oxidation of CPWR and its role in immobilizing low-concentration Cu (10 mg L?1) under weakly acidic leach (pH = 5.0). The experimental results indicated that the breakthrough capacity was around 14.0 mg Cu g?1 CPWR when Cu2+ breakthrough concentration was 0.5 mg L?1. Sequential extraction of Cu and dithionite–citrate–bicarbonate extraction of free iron in the used CPWR after the column breakthrough indicated that Cu removal by CPWR consisted of the following processes: oxidation of pyrite and dissolution of siderite in CPWR, ferrous oxidation, and adsorption of Cu on ferric (hydr)oxides. This study shows the potential application of CPWR as an effective sorbent for the removal of low-concentration Cu from acid mine drainage.  相似文献   

10.
There are compelling economic and environmental reasons to remove pesticides from wastewater because they are toxic and carcinogenic. The effectiveness of copper-based metal–organic framework (Cu-BTC) for adsorbing the insecticide 14C-ethion from wastewater has been studied as function of contact time, adsorbent dosage, temperature and pH. 14C-ethion/Cu-BTC isotherms exhibit two plateaus (BET type IV) and are reliably represented by Brunauer–Deming–Deming–Teller and Zhu–Gu models, with deviations of only 1.99 and 3.95%, respectively. The removal curve measured under batch operation is well represented by a pseudo-first-order equation, yielding results equivalent to the theoretical linear driving force model of Glueckauf. At pH 7, 75 mg L?1 ethion concentration, 150 min, 25 °C and 0.425 g L?1 Cu-BTC dose, the sorbent capacity is ca. 122 mg g?1. Moreover, Cu-BTC has a good stability after six adsorptions cycles. Finally, our results disclose the fundamental understanding of the adsorption mechanism: the ethion molecule coordinates to two copper(II) atoms across the metal–organic framework channel via the phosphoryl (P–O) group.  相似文献   

11.
Benthic microalgae (BMA) inhabit the upper few centimeters of shelf sediments. This review summarizes the current information on BMA communities in the South Atlantic Bight (SAB) region of the Southeastern US continental shelf to provide insights into the potential role of these communities in the trophodynamics and biogeochemical cycling in shelf waters. Benthic irradiance is generally 2–6% of surface irradiance in the SAB region, providing sufficient light to support BMA primary production over 80–90% of the shelf width. BMA biomass greatly exceeds that of integrated phytoplankton biomass in the overlying water column on an areal basis. The SAB appears to have lower BMA biomass, but higher production than most temperate continental shelves. Annual production estimates average 101 and 89 g C m?2 year?1 for 5–20 and >?20 depth intervals, respectively. However, high variation in rates and biomass in time and space make comparisons between studies difficult. Submarine groundwater discharge (SGD) rather than the water column or in situ N regeneration from organic matter maybe the major “new” N source for BMA. The estimated supply of N (1.2 mmol N m?2 day?1) by SGD closely approximates the rates needed to support BMA primary production (3.1 to 1.6 mmol N m?2 day?1) in the sediments of the SAB. Identifying the source(s) of fixed N supporting the BMA community is essential for understanding the carbon dynamics and net ecosystem metabolism within the large area (76,000 km2) of the continental shelf in the SAB as well other temperate shelves worldwide.  相似文献   

12.
Due to its harmful impact on human health, the presence of heavy metals, metalloids and other toxic pollutants in drinking or irrigation water is a major concern. Recent studies have proved that nanosized adsorbents are significantly more effective than their microsized counterparts. Particular attention has been given to nanocomposites with nanoadsorbents embedded in matrixes that could provide stability to the material and contribute to eliminating problems that may appear when using conventional granular systems. This study presents the preparation of a novel hybrid filter from a commercially available polypropylene (PP) non-woven fabric matrix modified with multiwall carbon nanotubes (MWCNT) and iron oxy(hydroxide) nanoparticles, and its use in the removal of As(III). A Box–Behnken statistical experimental design has been chosen to explore relevant variables affecting the filter performance: (1) As(III) concentration, (2) pH and (3) sorbent dose. From an As(III) concentration of 10 mg L?1, at pH 6.5 and with a sorbent dose of 5 g L?1, the PP filter modified with MWCNT removes 10% of the initial metalloid concentration, reaching a capacity of 0.27 mg g?1. After modification with iron oxy(hydroxide), the performance of the material is largely enhanced. The filter, under the same conditions, removes 90% of the initial As(III) concentration, reaching a capacity almost tenfold higher (2.54 mg g?1). This work demonstrates that the developed hybrid filter is effective toward the removal of As(III) in a wide range of pHs. A cubic regression model to compute the removal of the filter as a function of pH and sorbent dose is provided.  相似文献   

13.
La Goulette, Rades and Sidi Bou Said harbours are considered as the most important commercial and tourist ports in the Gulf of Tunis. They are located on the northeast coast of Tunis and receive industrial and municipal wastewaters from Tunis city. The contamination level of copper, lead, zinc, cadmium, manganese, iron, total nitrogen and total organic carbon in the surface sediments was assessed on the basis of the enrichment index factors and corresponding to sediment quality guidelines. The results revealed moderate to highly elevated concentrations near to the sites of intense industrial, shipping and/or commercial activities suggesting a direct influence of these sources. In winter and summer, concentrations varied for cadmium, 0.28–1.40 mg kg?1; lead, 18–217 mg kg?1; zinc, 87–459 mg kg?1; copper, 8–121 mg kg?1; manganese, 208–254 mg kg?1; and for iron, 24–40 g kg?1. Furthermore, in summer the concentration of the total organic carbon and the total nitrogen contents range between 4.3–6.5 % and 0.06–0.49 % with an average value of 5.9 and 0.15 %, respectively. Whereas, in winter, total organic carbon and the total nitrogen concentrations varied between 2.3–9.6 % and 0.03–0.22 % with an average value of 6.1 and 0.14 %, respectively. The levels of lead, copper, zinc and iron in suspended particulate matter content range between 3.1–27.5 mg kg?1; 0.4–11.7 mg kg?1; 1–1.5 mg kg?1; 1.2–1.7 g kg?1, respectively. This study revealed that heavy metals pollution is mainly localized in the commercial (Rades) and fishing (La Goulette) harbours and not in the yachting (Sidi Bou Said) harbour.  相似文献   

14.
Microwave-assisted tetrabutyl ammonium-impregnated sulphate-crosslinked chitosan was synthesized for enhanced adsorption of hexavalent chromium. The adsorbent obtained was extensively characterized using Fourier transform infrared, X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray studies. Various isotherm models such as Langmuir, Freundlich and Dubinin–Radushkevich were studied to comprehend the adsorption mechanism of hexavalent chromium by the adsorbent. Maximum adsorption capacity of 225.9 mg g?1 was observed at pH 3.0 in accordance with Langmuir isotherm model. The sorption kinetics and thermodynamic studies revealed that adsorption of hexavalent chromium followed pseudo-second-order kinetics with exothermic and spontaneous behaviour. A column packed with 1 g of adsorbent was found to give complete adsorption of Cr(VI) up to 900 mL of 200 mg L?1 solution which discerns the applicability of the adsorbent material for higher sample volumes in column studies. The effective adsorption results were obtained due to both ion exchange and ion pair interaction of adsorbent with hexavalent chromium. Greener aspect of overall adsorption was regeneration of the adsorbent which was carried out using sodium hydroxide solution. In the present study, the regenerated adsorbent was effectively reused up to ten adsorption–desorption cycles with no loss in adsorption efficiency.  相似文献   

15.
This article reports on the utilization of chemically modified cellulosic sago (MCS) from sago bark as a highly potential material for remediating oil spills in marine environment. MCS was prepared via incorporation of hydroxyl-rich cellulosic sago bark (CS) with fatty acid derivative. The sorption capacity, hydrophobicity, and lipophilicity of MCS and CS were evaluated. MCS exhibited higher total pore volume (0.012 cm3/g) and high hydrophobicity (60%) compared to CS. The oil spills adsorption studies was compared in batch system both in deionized water and seawater. MCS showed higher oil sorption capacity in deionized water after 60 min (MCS 3.0 g/g, CS 2.4 g/g). The maximum oil sorption capacity of MCS in dynamic seawater system was 5.7 g/g which was higher than CS (5.0 g/g). The results suggested that MCS is a potential low-cost natural sorbent which work best in the removal of oil spilled from dynamic seawater environment than deionized water.  相似文献   

16.
Tetraethylenepentamine-modified sugarcane bagasse (SCB) was prepared to improve its adsorption capacity and selectivity toward Cu2+. Adsorption performances of the modified sorbent for Cu2+ were studied in batch system. Separation of Cu2+ from Pb2+ by the modified sorbent fixed-bed column were studied under dynamic system with initial molar concentration ratio \(\left( {C_{0}^{\text{Cu}} /C_{0}^{\text{Pb}} } \right)\) ranging from 1:1 to 1:100. The amount of Cu2+ and Pb2+ adsorbed on the saturated column was calculated by the elution curve. Batch experimental results showed that the adsorption capacity of the sorbent for Cu2+ increased from 0.12 to 0.21 mmol g?1 after modification. Dynamic adsorption results showed that the modified SCB had higher adsorption affinity toward Cu2+ than Pb2+. 0.07 mmol g?1 of adsorbed Pb2+ was pushed off by Cu2+ during the competitive adsorption process at \(C_{0}^{\text{Cu}} /C_{0}^{\text{Pb}} = {\text{1:1}}.\) The breakthrough curves and adsorption kinetics of Cu2+ in the column could be fitted well by the Yoon–Nelson and modified Yoon–Nelson model, respectively. According to the elution curve, the amount of Cu2+ adsorbed on the fixed-bed column were 0.16, 0.16 and 0.15 mmol g?1, while that of Pb2+ were 0.0016, 0.0051 and 0.0094 mmol g?1 when \(C_{0}^{\text{Cu}} /C_{0}^{\text{Pb}}\) increased from 1:1 to 1:10 and 1:100. Cu2+ could be selectively adsorbed and separated from Pb2+ by using the modified sorbent fixed-bed column.  相似文献   

17.
Cathodoluminescence (CL) spectra of unirradiated, He+ ion-implanted and electron-irradiated plagioclase minerals contain the following emission bands: (1) below 300 nm due to Pb2+, (2) at ~320 and ~350 nm to Ce3+, (3) at 380–420 nm to Eu2+, Ti4+ and/or Al–O?–Al/Ti defects, (4) at 560–580 nm to Mn2+ and (5) at 720–760 nm to Fe3+. During the implantation of He+ ion, much of their energy may be dissipated by partial destruction and strain of the feldspar framework, resulting in quenching of CL. Deconvolution of CL spectra acquired from albite and oligoclase reveals an emission component at 1.86 eV (666 nm) assigned to a radiation-induced defect center associated with Na+ atoms. As its intensity increases with radiation dose, this emission component has potential for geodosimetry and geochronometry. Electron irradiation causes Na+ migration in plagioclase, and then a considerable reduction in intensity of emissions assigned to impurity centers, which is responsible for an alteration in the energy state or a decrease in luminescence efficiency following the change of activation energy. Emission intensity at 1.86 eV positively correlates with electron irradiation time for unimplanted and He+ ion-implanted albite and oligoclase, but negatively for the implanted albite above 1.07 × 10?4 C/cm2. It implies that radiation halo produced by α-particles should not be measured using CL spectroscopy to estimate β radiation dose on albite in the high radiation level.  相似文献   

18.
《Applied Geochemistry》2001,16(5):531-539
Geomaterials can be cost-effective sorbents for use in water treatment. In this study, a heavily-weathered Tertiary soil from Xinzhou, China was used as a sorbent for defluoridation of high-fluoride drinking water. The soil is composed of quartz, feldspar, illite and goethite, with an Fe oxide content of 6.75%. Batch and column experiments were done to characterize the F− removal properties and to develop an optimal activation and regeneration procedure. The soil can be regenerated following a simple base-acid rinsing procedure. This can be performed in situ, i.e., by passing the rinsing solutions directly through the treatment column. The same regeneration procedure can be used to activate the pristine soil. Fluoride sorption is described by a Freundlich isotherm model and the bulk of the uptake occurs within 1.5 h. Iron oxide coatings on soil particles and perhaps ≡FeOH surface groups at particle edges of illite grains are likely responsible for the soil's F-sorption property. As collected in the field, the soil has a low permeability and is thus unsuitable for direct use in a flow-through column. Heat-treatment at 400–500°C for 2 h, however, produces a granular and permeable sorbent. Although the soil's sorption capacity (150 μg/g ) is about a quarter of the low end range of values reported for commercially-available activated alumina, the sorption for F− is specific. A batch sorption experiment in the presence of Cl−, SO42− and HCO3− shows little or no competition from these other anions.  相似文献   

19.
We performed in situ infrared spectroscopic measurements of OH bands in a forsterite single crystal between ?194 and 200 °C. The crystal was synthesized at 2 GPa from a cooling experiment performed between 1,400 and 1,275 °C at a rate of 1 °C per hour under high silica-activity conditions. Twenty-four individual bands were identified at low temperature. Three different groups can be distinguished: (1) Most of the OH bands between 3,300 and 3,650 cm?1 display a small frequency lowering (<4 cm?1) and a moderate broadening (<10 cm?1) as temperature is increased from ?194 to 200 °C. The behaviour of these bands is compatible with weakly H-bonded OH groups associated with hydrogen substitution into silicon tetrahedra; (2) In the same frequency range, two bands at 3,617 and 3,566 cm?1 display a significantly anharmonic behaviour with stronger frequency lowering (42 and 27 cm?1 respectively) and broadening (~30 cm?1) with increasing temperature. It is tentatively proposed that the defects responsible for these OH bands correspond to H atoms in interstitial position; (3) In the frequency region between 3,300 and 3,000 cm?1, three broad bands are identified at 3,151, 3,178 and 3,217 cm?1, at ?194 °C. They exhibit significant frequency increase (~20 cm?1) and broadening (~70 cm?1) with increasing temperature, indicating moderate H bonding. These bands are compatible with (2H)Mg defects. A survey of published spectra of forsterite samples synthesized above 5 GPa shows that about 75 % of the incorporated hydrogen belongs to type (1) OH bands associated with Si substitution and 25 % to the broad band at 3,566 cm?1 (type (2); 3,550 cm?1 at room temperature). The contribution of OH bands of type (3), associated to (2H)Mg defects, is negligible. Therefore, solubility of hydrogen in forsterite (and natural olivine compositions) cannot be described by a single solubility law, but by the combination of at least two laws, with different activation volumes and water fugacity exponents.  相似文献   

20.
Seafloor methane emission from the Quepos Slide on the submarine segment of the Costa Rica fore-arc margin was estimated by extrapolating flux measurements from individual seeps to the total area covered by bacterial mats. This approach is based on the combination of detailed mapping to determine the abundance of seeps and the application of a numerical model to estimate the amount of benthic methane fluxes. Model results suggest that the majority of the studied seeps transport rather limited amount of methane (on average: ~177 μmol cm?2 a?1) into the water column due to moderate upward advection, allowing for intense anaerobic oxidation of methane (AOM; on average: 53 % of the methane flux is consumed). Depth-integrated AOM rates (56–1,538 μmol CH4 cm?2 a?1) are comparable with values reported from other active seep sites. The overall amount of dissolved methane released into the water column from the entire area covered by bacterial mats on the Quepos Slide is estimated to be about 0.28 × 106 mol a?1. This conservative estimate which relies on rather accurate determinations of seafloor methane fluxes emphasizes the potential importance of submarine slides as sites of natural methane seepage; however, at present the global extent of methane seepage from submarine slides is largely unknown.  相似文献   

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