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1.
New bio-adsorbent carbon materials were synthesized from the leaves and veins of Mucuna pruriens and Manihot esculenta plants, which are locally available in abundance. The synthesized carbons were activated using 0.01N HNO3. Surface area of the activated carbons from M. pruriens and M. esculenta plants was found to be quite high, i.e., 918 and 865 m2/g, respectively. Scanning electron microscopy analysis of the carbons reflects complex disorganized surface structures of different open pore sizes, shapes and dimensions. These properties of the newly synthesized activated carbons led to the development of a sand-supported carbon column, for its possible use in the removal of coliform bacteria and Escherichia coli (E. Coli) from raw water samples. The removal percentage of E. coli was found to be 100% with both the types of carbon adsorbents, as confirmed from the McCardy most probable number table. Similarly, the removal percentage of coliform bacteria was found to be 99 and 98.7% by M. pruriens and M. esculenta carbon columns, respectively. These activated carbons synthesized from locally available plants possess the characteristics of good low-cost adsorbents which can be easily used for the removal of bacteria from water by adsorption method.  相似文献   

2.
The use of agricultural wastes as biosorbents is gaining importance in bioremediation of heavy metal-polluted water and soils, due to their effectiveness and low cost. This work assesses the Cd, Pb and Cu adsorption capacity of the raw materials used in the production of substrates for mushroom production (Agaricus bisporus and Pleurotus ostreatus) and the spent mushroom composted (SMC), based on the functional groups of their organic carbon. The raw materials studied included agricultural wastes (wheat straw, wheat and rice poultry litter, grape pomace) and inorganic substances (gypsum and calcareous sand). Organic carbon from wastes and their composting products were characterized by CP-MAS 13C NMR. Langmuir adsorption isotherms of metals were plotted for each raw material, composting step, spent A. bisporus and P. ostreatus substrates and the final SMC. The maximum adsorption capacities of SMC were 40.43, 15.16 and 36.2 mg g?1 for Cd, Pb and Cu, respectively. The composting process modified the adsorption properties of raw materials because of the enhanced adsorption of Cd and Cu and decreased adsorption capacity of Pb. CP-MAS 13C NMR and potentiometric titration were used to identify the functional groups of the organic carbon responsible for the metal adsorption. The content of cellulose was correlated with Pb adsorption (p < 0.001), alkyl and carboxyl carbon with Cd adsorption (p < 0.001), and N-alkyl (p < 0.001) and carboxyl (p < 0.010) groups with Cu adsorption. These results are valuable to develop new biosorbents based on agricultural wastes and demonstrate the high potential of SMC to adsorb heavy metals from polluted environments.  相似文献   

3.
In this work, castor cake produced as a by-product in castor oil extraction was used for activated carbon production. Castor cake was chemically treated with a K2CO3 solution, and the effect of the pyrolysis temperature in the 500–900 °C range was studied. Materials were characterized by X-ray powder diffraction, thermogravimetric analysis, scanning electron microscopy and nitrogen adsorption–desorption at ?196 °C. Methylene blue adsorption was selected as a test probe to stress the removal capacity of the prepared materials. By the X-ray powder diffraction analysis, carbon obtaining in its graphite allotropic form together with other inorganic compounds was verified. Scanning electron microscopy images evidenced the generation of porosity in the thermally treated samples compared with the pristine compound. In addition, the specific surface area values augmented progressively with the thermal treatment increment achieving a value of 1015 m2 g?1 in the 900 °C calcined sample. Calcination at 800 °C and m/V = 0.003 ratio were the best parameter combination to achieve a 99.6% methylene blue uptake.  相似文献   

4.
This work aimed to investigate the adsorption characteristics, both kinetically and thermodynamically, of Cu(II) and Pb(II) removal from aqueous solutions onto mixed-waste activated carbon, as well as to study the competitive behavior found in mixed heavy metal solution systems. This study shows that activated carbon prepared from mixed waste is an effective adsorbent for the removal of Cu(II) and Pb(II) from aqueous solutions, with the aim of detoxifying industrial effluents before their safe disposal onto water surfaces. The adsorption process was characterized in terms of kinetic and thermodynamic studies. In addition, the influence of presence of Cu(II) and Pb(II) in a competitive system was investigated. The results showed that the maximum adsorption capacities were gained at a pH of 6 with a contact time of 180 min, a metal solution concentration of 300 ppm, and an adsorbent dose of 0.3 g/L. The adsorption process was found to follow a pseudo-first-order kinetic model. Thermodynamic parameters such as ΔG o, ΔH o, and ΔS o showed that the sorption process was spontaneous and endothermic in nature. A competitive study demonstrated the applicability of mixed-waste activated carbon to adsorb Cu(II) and Pb(II) from a solution of mixed metals. In addition, the adsorption capacity was found to be as effective as other adsorbents reported in the literature. The developed adsorptive removal procedure was applied for treatment of real wastewater samples and showed high removal efficiency.  相似文献   

5.
Acacia nilotica was used for the adsorption of Reactive Black 5 (RB5) dye from an aqueous solution. Both the raw and activated (with H3PO4) carbon forms of Acacia nilotica (RAN and ANAC, respectively) were used for comparison. Various parameters (including dye concentration, contact time, temperature, and pH) were optimized to obtain the maximum adsorption capacity. RAN and ANAC were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The maximum experimental adsorption capacities for RAN and ANAC were 34.79 and 41.01 mg g?1, respectively, which agreed with the maximum adsorption capacities predicted by the Langmuir, Freundlich, and Dubinin–Radushkevich equilibrium isotherm models. The adsorption data of ANAC showed a good fit to the isotherm models based on the coefficient of determination (R 2): Langmuir type II (R 2 = 0.99) > Freundlich (R 2 = 0.9853) > Dubinin–Radushkevich (R 2 = 0.9659). This result suggested monolayer adsorption of RB5 dye. The adsorption of RB5 dye followed pseudo-second-order kinetics. The RAN adsorbent reflected an exothermic reaction (enthalpy change, ΔH = ?0.006 kJ mol?1) and increased randomness (standard entropy change, ΔS = 0.038 kJ mol?1) at the solid–solution interface. In contrast, ANAC reflected both exothermic [?0.011 kJ mol?1 (303–313 K)] and endothermic [0.003 kJ mol?1 (313–323 K)] reactions. However, the ΔS value of ANAC was lower when the RB5 adsorption increased from 313 to 323 K. The negative values for the Gibbs free energy change at all temperatures indicated that the adsorption of RB5 dye onto RAN and ANAC was spontaneous in the forward direction.  相似文献   

6.
Rapid increases in the amounts of fullerene C60 nanoparticles (nC60) being produced and used will inevitably lead to increases in the amounts released into the aquatic environment. This will have implications for human and ecosystem health. Wastewater treatment plants are key barriers to nC60 being released into aquatic systems, but little information is available on how adsorption processes in wastewater treatment plants affect the fates of nC60. We investigated the effects of the surface properties of activated sludge on the adsorption of nC60 and related mechanisms by modeling the adsorption kinetics and equilibrium process and performing correlation analyses. The adsorption of nC60 closely followed the pseudo-second-order kinetic model (R > 0.983), the Freundlich isotherm model (R > 0.990), and the linear partitioning isotherm model (R > 0.966). Different adsorption coefficients, 1.070–4.623 for the Freundlich partitioning model and 1.788–6.148 for the linear partitioning model, were found for different types of activated sludge. The adsorption coefficients significantly positively correlated with the zeta (ζ) potential (R = 0.877) and hydrophobicity (R = 0.661) and negatively correlated with particle size (R = ?0.750). The results show that nC60 adsorption is strongly affected by the surface properties of activated sludge because changes in surface properties cause changes in the electrostatic and hydrophobic interactions that occur.  相似文献   

7.
Indole is a highly recalcitrant aromatic heterocyclic organic compound consisting of a five-membered nitrogen-containing pyrrole ring fused to a six-membered benzene ring. This study presents the results of the electro-chemical mineralization of indole in an aqueous solution using platinum-coated titanium (Pt/Ti) electrode. A central composite design was used to investigate the effect of four parameters namely initial pH (pHo), current density (j), conductivity (k) and treatment time (t) at 5 levels. Multiple responses namely chemical oxygen demand (COD) removal (Y 1) and specific energy consumption (Y 2) were simultaneously maximized and minimized, respectively, by optimizing the parameters affecting the mineralization of indole by using the desirability function approach. At the operating conditions of pH 8.6, j = 161 A/m2, k = 6.7 mS/cm and t = 150 min, 83.8% COD removal with specific energy consumption of 36.3 kWh/kg of COD removed was observed. Ultra performance liquid chromatography, UV–visible spectroscopy, Fourier transform infrared spectroscopy and cyclic voltammetry of the indole solution were performed at the optimum condition of the treatment so as to report a plausible mechanism of indole degradation. Field emission scanning electron microscopy analysis of electrodes before and after treatment was performed for determining the changes on anode surface during the treatment. Thermal analysis of the solid residue (scum) obtained was also performed for exploring its disposal prospects. Present study shows that electro-chemical oxidation can be used for mineralization of nitrogenous heterocyclic compounds such as indole.  相似文献   

8.
Evans blue (EB) dye has been successfully removed from aqueous solution through chemisorption process with synthetic layered double hydroxides (LDH) [Zn1?x Al x (OH)2NO3·nH2O, x = 0.2–0.33]. Detailed evaluation of dye adsorption characteristics in aqueous medium has been studied for different layer charged hydroxides. The objective of the study was efficient removal of a dye by LDH and understanding the structure–property relationship of the LDH on its adsorption behaviour. Highest Langmuir monolayer adsorption capacity (Qt) of 113.64 mg g?1 was observed for highest layer charge x = 0.33, and it is higher than previously reported values for the LDH-EB dye system. Under optimized condition, 99% of EB dye is removed from aqueous solution within 60 min at 313 K. The monotonous increase in Qt value with increasing layer charge is correlated with layer charge density (LCD) and lower particle size of the synthetic LDH. The variation in Qt among different layer charged materials is marginal (3.46–4.17%) with respect to the respective anion exchange capacity (AEC) of LDH NO3. The limited contribution of AEC surmises the occurrence of surface-only adsorption and absence of intercalation as validated by the XRD analysis. The spontaneity of the EB dye removal increases with increasing temperature and LCD. The chemisorption nature of the adsorption reaction is well supported by the thermodynamics values.  相似文献   

9.
Vitis vinifera (grape) leaf litter, an abundant agricultural waste in South Africa was chemically modified with H3PO4 and carbonized for use as biosorbent. Characterization and the potential application of the adsorbent in simultaneous removal of 4-nitrophenol and 2-nitrophenol from aqueous solutions were investigated. The adsorbent was characterized using FTIR, SEM and EDX elemental microanalysis. The EDX and FTIR analysis revealed the presence of surface oxygen moieties capable of binding to adsorbate molecules while the SEM micrographs showed the development of pores and cavities in the adsorbent. Batch adsorption experiments were conducted at a varying contact time, adsorbent dosage, pH and initial adsorbate concentration to investigate optimal conditions. The maximum adsorption capacity of the adsorbent was 103.09 and 103.10 mg/g for 4-nitrophenol and 2-nitrophenol, respectively. The adsorption process was best fitted into Freundlich isotherm while the adsorption kinetics followed a pseudo-second-order model. Liquid film and intra-particle diffusion contributed to the adsorption process. Thermodynamic parameters of ΔG°, ΔH° and ΔS° were evaluated. The adsorption was exothermic, feasible and spontaneous. The results suggest a possible application of grape leaf litter as a precursor for activated carbon and for cheaper wastewater treatment technologies.  相似文献   

10.
Here, a novel one-dimensional composite of poly(m-phenylenediamine)s coating on filamentous Streptomyces was successfully constructed via a controllable polymerization reaction. The synthesized composites were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Their adsorption isotherm and kinetics for aqueous hexavalent chromium were also systematically examined. The results of scanning electron microscopy analysis indicated that the obtained composites based on Streptomyces were showed a uniform and stable one-dimensional morphology with distinct core–shell configuration. Moreover, the Langmuir isotherm model (R 2 > 0.96) and pseudo-second-order equation (R 2 = 0.9996) described well the equilibrium adsorption behavior and kinetics of hexavalent chromium adsorption by the composites. In addition, bath adsorption experiments demonstrated the highest adsorption capacity of hexavalent chromium by the composites reached 320.03 mg g?1 in an acid solution, which was 5.6 times as that of the pure Streptomyces filaments. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses suggested that the adsorption of hexavalent chromium by the composites possibly involved the protonation, redox, and chelation reactions. Therefore, a promising application of these composites in treating acid hexavalent chromium-contaminated wastewater is expectable.  相似文献   

11.
Tibetan Plateau (TP) is the highest and most extensive plateau in the world and has been known as the roof of the world, and it is sensitive to climate change. The researches of CO2 fluxes (F C) in the TP region play a significant role in understanding regional and global carbon balance and climate change. Eddy covariance flux measurements were conducted at three sites of south-eastern TP comprising Dali (DL, cropland ecosystem), LinZhi (LZ, alpine meadow ecosystem) and Wenjiang (WJ, cropland ecosystem); amongst those DL and LZ are located in plateau region, while WJ is in plain region. Dynamics of F C and influences of vegetation, meteorological (air temperature, photosynthetically active radiation, soil temperature and soil water content) and terrain factors (altitude) were analysed on the basis of data taken during 2008. The results showed that, in the cool sub-season (March, April, October and December), carbon sink appeared even in December with fluxes of (?0.021 to ?0.05) mg CO2 m?2 s?1 and carbon source only in October (0.03 ± 0.0048) mg CO2 m?2 s?1 in DL and WJ site. In LZ site, carbon sink was observed in April: (?0.036 ± 0.0023) mg CO2 m?2 s?1 and carbon sources in December and March (0.008–0.010 mg CO2 m?2 s?1). In the hot sub-season (May–August), carbon source was observed only in May with (0.011 ± 0.0022), (0.104 ± 0.0029) and (0.036 ± 0.0017) fluxes in LZ, DL and WJ site, respectively, while carbon sinks with (?0.021 ± 0.0041), (?0.213 ± 0.0007) and (?0.110 ± 0.0015) mg CO2 m?2 s?1 fluxes in LZ, DL, and WJ, respectively. Comparing with plain region (WJ), carbon sinks in plateau region (DL and LZ) lasted for a longer time, and the absorption sum was large and up to (–357.718 ± 0.0054) and (?371.111 ± 0.0039) g C m?2 year?1, respectively. The LZ site had the weakest carbon sink with (?178.547 ± 0.0070) g C m?2 year?1. Multivariate analysis of covariance showed that altitude (AL) as an independent factor explained 39.5 % of F C (P < 0.026). F C had a quadratic relationship with Normalized difference vegetation index (NDVI) (R 2 ranges from 0.485 to 0.640 for three sites), an exponential relationship with soil temperature at 5-cm depth (ST 5) at night time and a quadratic relationship with air temperature (T a) at day time. Path analysis indicated that photosynthetically active radiation (PAR), sensible heat fluxes (H) and other factors all had direct or indirect effects on F C in all of the three tested sites around the south-eastern TP.  相似文献   

12.
Effects of initial concentrations of Moringa oleifera seed coagulant for removing Chemical Oxygen Demand and Total Dissolved Solids from municipal solid waste leachate have been evaluated at an optimum pH of 7 and temperature of 318 K. The kinetic data obtained from the experiments were fitted to the pseudo first-order, pseudo second-order, Elovich and intraparticle diffusion models. Based on a regression coefficient (R 2), the equilibrium (kinetic) data were best fitted with the Elovich model (R 2 = 0.993 for Chemical Oxygen Demand and R 2 = 0.996 for Total Dissolved Solids) than that of other models. The results of the kinetic models study indicated that the adsorption capacity of M. oleifera seed as a coagulant for removing Chemical Oxygen Demand and Total Dissolved Solids in a leachate increased up to 100 mg L?1, beyond which the adsorption capacity got reduced. Finally, the present study concluded that M. oleifera seed coagulant could be employed effectively for the removal of Chemical Oxygen Demand and Total Dissolved Solids in a municipal solid waste leachate.  相似文献   

13.
This study investigated the removal efficiency of pharmaceuticals from aqueous solutions supported on chemically treated fly ash. The coal fly ash was supplied by the electric power station in Krakow, Poland. There are plenty of studies showing the utilization of fly ash as a low-cost adsorbent for wastewater containing heavy metals or dyes. Adsorption and immobilization of pharmaceuticals and personal care products on fly ash is a relatively new method but it is a very promising one. In this study, the adsorptive removal of diclofenac, ketoprofen, carbamazepine, bezafibrate, bisphenol A, 17α-ethinyl estradiol and estriol by HCl- and NaOH-treated fly ash was assessed. Chemical treatment of fly ash changed structures of particles and enhanced specific surface areas. HCl-treated fly ash was characterized by the highest BET specific surface area 47.9 m2 g?1 and unburned carbon content 8.1%. Isotherms for all compounds except for 17α-ethinyl estradiol (EE2) and estriol (E3) were linear. Higher linear regression coefficients (R 2) obtained for isotherms of EE2 and E3 show that the Freundlich model better describes their sorption. Adsorption coefficients K d varied between 109.5 (L kg?1) for bisphenol A and 471.5 (L kg?1) for bezafibrate. Freundlich constants (K F) for EE2 and E3 were 62.3 and 119.9 (µg1?1/n L1/n kg?1), respectively. Acid treatment of fly ash increased adsorption of diclofenac, ketoprofen, carbamazepine, bezafibrate and bisphenol A. Comparison of the octanol–water partitioning coefficients (log K OW) with the partitioning coefficients normalized on unburned carbon content (log K UC) revealed similarities but no strong correlation. The increasing of unburned carbon increased sorption of compounds to fly ash.  相似文献   

14.
Fine sediment inputs can alter estuarine ecosystem structure and function. However, natural variations in the processes that regulate sediment transport make it difficult to predict their fate. In this study, sediments were sampled at different times (2011–2012) from 45 points across intertidal sandflat transects in three New Zealand estuaries (Whitford, Whangamata, and Kawhia) encompassing a wide range in mud (≤63 μm) content (0–56 %) and macrofaunal community structure. Using a core-based erosion measurement device (EROMES), we calculated three distinct measures of sediment erosion potential: erosion threshold (? c ; N m?2), erosion rate (ER; g m?2 s?1), and change in erosion rate with increasing bed shear stress (m e ; g N?1 s?1). Collectively, these measures characterized surface (? c and ER) and sub-surface (m e ) erosion. Benthic macrofauna were grouped by functional traits (size and motility) and data pooled across estuaries to determine relationships between abiotic (mud content, mean grain size) and biotic (benthic macrofauna, microbial biomass) variables and erosion measures. Results indicated that small bioturbating macrofauna (predominantly freely motile species <5 mm in size) destabilized surface sediments, explaining 23 % of the variation in ? c (p ≤ 0.01) and 59 % of the variation in ER (p ≤ 0.01). Alternatively, mud content and mean grain size cumulatively explained 61 % of the variation in m e (p ≤ 0.01), where increasing mud and grain size stabilized sub-surface sediments. These results highlight that the importance of biotic and abiotic predictors vary with erosion stage and that functional group classifications are a useful way to determine the impact of benthic macrofauna on sediment erodibility across communities with different species composition.  相似文献   

15.
High-pressure phase transitions of CaRhO3 perovskite were examined at pressures of 6–27 GPa and temperatures of 1,000–1,930°C, using a multi-anvil apparatus. The results indicate that CaRhO3 perovskite successively transforms to two new high-pressure phases with increasing pressure. Rietveld analysis of powder X-ray diffraction data indicated that, in the two new phases, the phase stable at higher pressure possesses the CaIrO3-type post-perovskite structure (space group Cmcm) with lattice parameters: a = 3.1013(1) Å, b = 9.8555(2) Å, c = 7.2643(1) Å, V m  = 33.43(1) cm3/mol. The Rietveld analysis also indicated that CaRhO3 perovskite has the GdFeO3-type structure (space group Pnma) with lattice parameters: a = 5.5631(1) Å, b = 7.6308(1) Å, c = 5.3267(1) Å, V m  = 34.04(1) cm3/mol. The third phase stable in the intermediate P, T conditions between perovskite and post-perovskite has monoclinic symmetry with the cell parameters: a = 12.490(3) Å, b = 3.1233(3) Å, c = 8.8630(7) Å, β = 103.96(1)°, V m  = 33.66(1) cm3/mol (Z = 6). Molar volume changes from perovskite to the intermediate phase and from the intermediate phase to post-perovskite are –1.1 and –0.7%, respectively. The equilibrium phase relations determined indicate that the boundary slopes are large positive values: 29 ± 2 MPa/K for the perovskite—intermediate phase transition and 62 ± 6 MPa/K for the intermediate phase—post-perovskite transition. The structural features of the CaRhO3 intermediate phase suggest that the phase has edge-sharing RhO6 octahedra and may have an intermediate structure between perovskite and post-perovskite.  相似文献   

16.
Novel bionanocomposites, S. cerevisiae–AgNPs, were synthesized by in situ formation of AgNPs on S. cerevisiae surface using fulvic acids as reductants under simulated sunlight. S. cerevisiae–AgNPs were characterized using UV–Vis spectroscopy, scanning electron microscope, transmission electron microscope and Fourier transform infrared spectroscopy. These analyses showed that AgNPs were distributed on the surface of S. cerevisiae. The application of S. cerevisiae–AgNPs in bacteria killing and heavy metal removal was studied. S. cerevisiae–AgNPs effectively inhibited the growth of E. coli with increasing concentrations of S. cerevisiae–AgNPs. E. coli was killed completely at high concentration S. cerevisiae–AgNPs (e.g., 100 or 200 µg mL?1). S. cerevisiae–AgNPs as excellent heavy metal absorbents also have been studied. Using Cd2+ as model heavy metal, batch experiments confirmed that the adsorption behavior fitted the Langmuir adsorption isotherms and the Cd2+ adsorption capacity of S. cerevisiae–AgNPs was 15.01 mg g?1. According to adsorption data, the kinetics of Cd2+ uptake by S. cerevisiae–AgNPs followed pseudo second-order kinetic model. Moreover, S. cerevisiae–AgNPs possessed ability of different heavy metals’ removal (e.g., Cr5+, As5+, Pb2+, Cu2+, Mn2+, Zn2+, Hg2+, Ni2+). The simulated contaminated water containing E. coli, Cd2+ and Pb2+ was treated using S. cerevisiae–AgNPs. The results indicated that the bionanocomposites can be used to develop antibacterial agents and bioremediation agents for water treatment.  相似文献   

17.
This research focused on the application of response surface methodology (RSM) for the removal of ethylbenzene by the graphene oxide grafted with polymethyl vinyl ketone and aniline (GO-MVK-ANI) from wastewater. The adsorbent was prepared through polymerization of graphene oxide with methyl vinyl ketone using ammonium persulfate initiator and further modification by aniline. The synthesized material was characterized via Fourier transform infrared resonance spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Brunauer–Emmett–Teller analysis. RSM was used to minimize the number of experiments and investigate the effect of three selected parameters (contact time, initial pH and adsorbent dose) on the removal efficiency of ethylbenzene. Additionally, the affecting parameters were optimized based on the selected target (ethylbenzene removal efficiency). The results show that 73% ethylbenzene could be adsorbed with initial ethylbenzene concentration of 20 mg/l under the optimum conditions (the contact time of 11 min, pH of 5.64 and adsorbent dose of 3.75 g/l). In this paper, high R 2-value (97.18%) for ethylbenzene removal and a good agreement with adjusted R 2-value (94.65%) indicated that the model was successful and the results demonstrated a reasonable proportion of the experimental and the predicted results.  相似文献   

18.
In this study, teff (Eragrostis tef) straw has been chemically treated and tested as an adsorbent for Cr(VI) removal. Chemically treatment of teff straw was done by NaOH, H3PO4 and ZnCl2 solutions. Scanning electron micrograph and X-ray diffraction were used for anatomical characterization, whereas Fourier transform infrared spectroscopy was used for surface change characterization of adsorbents. Effects of different experimental parameters like pH (2–12), initial Cr(VI) concentration (100–900 mg/L), adsorbent dose (2.5–20 g/L), contact time (15–360 min) and temperature (288–318 K) were studied. Temperature increment was found to stimulate the adsorption process. Langmuir isotherm was found to give better representation over wide range of temperature for untreated, H3PO4- as well as ZnCl2-treated teff straw, and Freundlich isotherm best represented the isotherm data for NaOH-treated teff straw. Maximum Cr(VI) adsorption capacity of untreated, NaOH-, H3PO4- and ZnCl2-treated teff straw was found to be 86.1, 73.8, 89.3 and 88.9 mg/g, respectively. Respective values of average effective diffusion coefficient (D e) were found to be 2.8 × 10?13, 2.59 × 10?14, 1.32 × 10?13 and 1.14 × 10?13 m2/s, respectively. The negative value of ΔG o for all the adsorbents indicates Cr(VI) spontaneous adsorption. Isosteric heat of adsorption (ΔH st,a) was found to vary with surface coverage (θ). ΔH st,a increased for untreated, H3PO4- and ZnCl2-treated teff straw, and decreased steadily with θ for NaOH-treated teff straw.  相似文献   

19.
A 4-week laboratory experiment investigated the behaviour (survival and bioirrigation) and impact of the invasive polychaetes Marenzelleria viridis, M. neglecta and M. arctia on sediment-water solutes exchange, porewater chemistry, and Fe and P interactions in high-salinity sandy sediment (HSS) and low-salinity muddy sediment (LSM) from the Baltic Sea. M. viridis showed deep burrowing with efficient bioirrigation (11 L m?2 day?1) and high survival (71%) in HSS, while M. arctia exhibited shallow burrowing with high bioirrigation (12 L m?2 day?1) and survival (88%) in LSM. M. neglecta behaved poorly in both ecological settings (bioirrigation, 5–6 L m?2 day?1; survival, 21–44%). The deep M. viridis bioirrigation enhanced total microbial CO2 (TCO2) production in HSS by 175% with a net efflux of NH4+ and PO43?, at rates 3- to 27-fold higher than for the other species. Although the shallow and intense bioirrigation of M. arctia in LSM stimulated microbial TCO2 production to some extent (61% enhancement), the nutrient fluxes close to zero indicate that it effectively prevented the P release. Porewater Fe:PO43? ratios revealed that the oxidizing effect of M. arctia bioirrigation increased the PO43? adsorption capacity of LSM twofold relative to defaunated controls while no buffering of PO43? was detected in M. viridis HSS treatment. Therefore, the different behaviour of the three species in various environments and the sharp contrast between M. viridis and M. arctia effects on C, N and P cycling must be considered carefully when the ecological role of Marenzelleria species in the Baltic Sea is evaluated.  相似文献   

20.
The high-pressure behavior of a vanadinite (Pb10(VO4)6Cl2, a = b = 10.3254(5), c = 7.3450(4) Å, space group P63/m), a natural microporous mineral, has been investigated using in-situ HP-synchrotron X-ray powder diffraction up to 7.67 GPa with a diamond anvil cell under hydrostatic conditions. No phase transition has been observed within the pressure range investigated. Axial and volume isothermal Equations of State (EoS) of vanadinite were determined. Fitting the P–V data with a third-order Birch-Murnaghan (BM) EoS, using the data weighted by the uncertainties in P and V, we obtained: V 0 = 681(1) Å3, K 0 = 41(5) GPa, and K′ = 12.5(2.5). The evolution of the lattice constants with P shows a strong anisotropic compression pattern. The axial bulk moduli were calculated with a third-order “linearized” BM-EoS. The EoS parameters are: a 0 = 10.3302(2) Å, K 0(a) = 35(2) GPa and K′(a) = 10(1) for the a-axis; c 0 = 7.3520(3) Å, K 0(c) = 98(4) GPa, and K′(c) = 9(2) for the c-axis (K 0(a):K 0(c) = 1:2.80). Axial and volume Eulerian-finite strain (fe) at different normalized stress (Fe) were calculated. The weighted linear regression through the data points yields the following intercept values: Fe a (0) = 35(2) GPa for the a-axis, Fe c (0) = 98(4) GPa for the c-axis and Fe V (0) = 45(2) GPa for the unit-cell volume. The slope of the regression lines gives rise to K′ values of 10(1) for the a-axis, 9(2) for the c-axis and 11(1) for the unit cell-volume. A comparison between the HP-elastic response of vanadinite and the iso-structural apatite is carried out. The possible reasons of the elastic anisotropy are discussed.  相似文献   

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