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1.
Abstract

The greenhouse industry aims to decrease phosphate discharge to help reduce eutrophication of surface waters, to reduce fertilizer consumption, and to maintain a more constant level of plant‐available phosphate. Iron and aluminum oxides and some aluminosilicate minerals are efficient sorbents for phosphate. The phosphate adsorption characteristics of synthetic hematite (α‐Fe2O3), goethite (α‐FeOOH), and allophane (Si3Al4O12 nH2O), and a commercial alumina (A12O3) were evaluated to determine their potential for reducing phosphate leaching from soilless root media. The pH dependence of phosphate adsorption and maximum adsorption capacities were determined by reacting each mineral with various levels of phosphate between pH 4.0 and 9.0 in a 10 mM potassium chloride (KCl) background solution. Adsorbed phosphate was determined by loss from solution. Adsorption envelopes (adsorbed phosphate versus pH) showed a decrease in phosphate adsorption with increasing pH, particularly for alumina and allophane, and at greater added phosphate concentrations. The maximum adsorption capacities per unit mass of the minerals at pH 5.4 decreased in the order allophane > alumina ? goethite > hematite. When expressed on a surface area basis, the order of maximum adsorption capacity remains the same except that alumina exceeded that of goethite. The allophane, goethite, and alumina sorbed enough phosphate that 3 to 9 g of these minerals would retain the amount of phosphate required for a high nutrient element requiring plant such as chrysanthemum.  相似文献   

2.
Phosphate sorption and desorption in soils are markedly influenced by iron oxides, although little is known on how the common iron oxides differ in their behaviour towards added phosphate. In this study, we investigated phosphate sorption and desorption in the clay fractions of 12 Terre Rosse that ranged widely in Fe oxide content, had very low contents of oxalate-extractable Fe oxides and different hematite/goethite ratios. Phosphate sorption at an equilibrium concentration of 1 mg P 1?1 was correlated with the goethite but not with the hematite content of the clay fractions. When phosphate was desorbed by electro-ultrafiltration, the difference in desorption half-time between untreated and deferrified clays was positively correlated with the goethite but not with the hematite content. These results suggest that goethite is more active than hematite in phosphate sorption and retention by soils.  相似文献   

3.
Phosphate reactions with natural allophane, ferrihydrite and goethite   总被引：5，自引：0，他引：5  
The reactions of phosphate with natural samples of allophane, ferrihydrite, hematite and goethite were measured for up to 30 d. The amount of phosphate sorbed on allophane showed the biggest increase with time whereas the amount sorbed on goethite showed the least increase with time. The total amount of phosphate sorbed either at high levels of phosphate addition or after 10 d followed the order hematite < goethite < ferrihydrite < allophane and was probably related to the specific surface. Si was desorbed as phosphate was adsorbed on the minerals.
The reactions of phosphate on allophane involved rapid, strong adsorption, probably at defect sites, followed by weaker adsorption, followed, probably, by disruption of the allophane structure together with precipitation of aluminium phosphates. Previous suggestions either of diffusive penetration of phosphate into surfaces or about the formation of aluminium phosphate coatings, are unlikely to hold for allophane, if all the Al is at the surface and if the structure can be ruptured.
The reactions of phosphate with iron oxides involved a rapid, strong ligand exchange, followed by weaker ligand exchange, and, probably, by a relatively slow penetration at defect sites and pores. Highly crystalline goethite has virtually no slow reaction and therefore solid-state diffusion of phosphate does not readily occur. The extent of phosphate uptake during the slow penetration reactions probably depends on the degree of crystallinity or porosity of iron oxides.
The most reactive adsorbents, such as allophane, ferrihydrite and Al-humus complexes do not have planar surfaces, and this needs to be considered when modelling phosphate reactions.  相似文献   

4.
Andosols and the soil components (allophanes, humic acids, and goethite) had been autoclaved to destroy the nuclease activity of soil microflora. DNA adsorption by allophanes and Andosols was decreased by increasing the amount of α-casein added to the allophanes and to soils up to casein concentration of 5 mg ml?1. DNA adsorption by humic acids was significantly increased by increasing the amount of α-casein up to 1.0 mg ml?1, whereas the addition of 20 mg α-casein ml?1 completely blocked DNA adsorption. These results can explain why the addition of excess skim milk is operationally needed for effective DNA extraction from Andosols. The amount of DNA adsorbed by Andosols treated with dephosphorylated α-casein was significantly higher than that of not treated Andosols (p?相似文献   

5.
The kinetics and heats of phosphate adsorption were measured on the <2 μm Na-saturated fractions of three allophanc-rich soils from Japan. Between 50 and 2250 μmol P g?1 as sodium phosphate were added to the soil fractions at pH 5 and pH 7, and at initial concentrations of 5 and 25 × 10?4m to avoid aluminium phosphate precipitation. An initial ‘instantaneous’ adsorption associated with exposed sites and, simultaneously, two inverse exponential rates of adsorption on internal and freshly forming external sites were observed. These rates are attributed to changes in the microstructure of allophane and to the desorption of organic matter held on allophanic surfaces. This interpretation is strongly supported by corresponding changes in the heats of adsorption with time. Calorimetry clearly indicates that when very large amounts of phosphate are added, new and very reactive surfaces are progressively exposed. More phosphate was adsorbed when the soil was acid and when the soil contained less organic matter.  相似文献   

6.
High phosphate (Pi) sorption in soils is a serious limiting factor for plant productivity and Pi fertilization efficiency, particularly in highly weathered and volcanic ash soils. In these soils, the sorbed Pi is so strongly held on the surfaces of reactive minerals that it is not available for plant root uptake. The use of phosphate-solubilizing microorganisms (PSM) capable of Pi desorption seems to be a complementary alternative in the management of these soils. The aim of this study was to evaluate the effectiveness of the soil fungus Mortierella sp., a known PSM, to desorb Pi from four soil minerals differing in their Pi sorption capacity. The fungus was effective in desorbing Pi from all tested minerals except from allophane, and its desorption depended on the production of oxalic acid. The effectiveness of the fungus to desorb Pi was ranked as montmorillonite > kaolinite > goethite > allophane. The quantity of desorbed Pi increased by increasing the amount of sorbed Pi. The Pi sorption capacity expressed as P0.2 value (amount of P required to increase a solution P concentration up to 0.2 mg L?1) was a good indicator of the effectiveness of Mortierella sp. to desorb Pi from soil minerals.  相似文献   

7.
Coleus (Plectranthus barbatus Andr.) is a medicinal herb whose roots contain forskolin. Incidences of soil-borne diseases, wilt complex and nematodes are the major limiting factors for growing this crop under soil media. Hence, an investigation was initiated for the standardization of soilless growth media and nutrient solution concentration in coleus. Coco peat, vermiculite, sand and their combinations were used as potting media with different concentrations of nutrients based on the recommended dose of fertilizers for soil media (1,080 mg plant?1 nitrogen, 960 mg plant?1 phosphorous and 1200 mg plant?1 potassium). Among the different media and nutrients, plants grown under coco peat media with 80% of the recommended dose of fertilizer for soil (864 mg plant?1 nitrogen, 768 mg plant?1 phosphorous and 960 mg plant?1 potassium) recorded significantly higher root yield (17.10 tha?1) and quality parameters (0.98% forskolin). Benefit–cost ratio was also recorded maximum (4.25) in the same treatment.  相似文献   

8.
Eight samples of goethite ranging in surface area from 18 to 132 m2 g-1 were mixed with phosphate at a range of pH values for periods which ranged from 0·5 h to 6 weeks. The sample with a surface area of 18 m2 g-1 had been hydrothermally treated to improve its crystallinity. Its rate of reaction with phosphate depended on pH but was complete within a day. Its maximum observed reaction was close to the theoretical maximum for surface adsorption of 2·5 μmol m?2. For the other samples, phosphate continued to react for up to 3 weeks and exceeded the value of 2·5 μmole m?2. The duration and extent of the reaction depended on the crystallinity of the goethite. The results were closely described by a model in which the phosphate ions were initially adsorbed on to charged external surfaces. The phosphate ions then diffused into the particles. This was closely described using equations for diffusion into a cylinder. Samples of goethite which had been loaded with phosphate dissolved more slowly in HCl, and had a longer lag phase, than phosphate-free goethite. For the hydrothermally treated goethite, HCl removed much of the phosphate when only a small proportion of the iron had been dissolved. For a poorly crystallized goethite, it was necessary to dissolve much more of the iron to obtain a similar removal of phosphate. Brief treatment with NaOH removed most of the phosphate from the hydrothermally treated goethite but only half the phosphate from a poorly crystallized goethite. These results are consistent with the idea that phosphate ions were not only bound on external surface sites but had also penetrated into meso- and micro-pores between the domains of the goethite crystals and were then adsorbed on internal surface sites. This penetration tied the domains together more firmly thus increasing the lag phase for dissolution. Differences between sites for phosphate adsorption are therefore caused mainly by their location on either external or internal sites. Models that ignore this are incomplete.  相似文献   

9.
The concentrations of Hg, Cu, Pb, Cd, and Zn accumulated by regional macrophytes were investigated in three tropical wetlands in Colombia. The studied wetlands presented different degrees of metal contamination. Cu and Zn presented the highest concentrations in sediment. Metal accumulation by plants differed among species, sites, and tissues. Metals accumulated in macrophytes were mostly accumulated in root tissues, suggesting an exclusion strategy for metal tolerance. An exception was Hg, which was accumulated mainly in leaves. The ranges of mean metal concentrations were 0.035?C0.953 mg g?1 Hg, 6.5?C250.3 mg g?1 Cu, 0.059?C0.245 mg g?1 Pb, 0.004?C0.066 mg g?1 Cd, and 31.8?363.1 mg g?1 Zn in roots and 0.033?C0.888 mg g?1 Hg, 2.2?C70.7 mg g?1 Cu, 0.005?C0.086 mg g?1 Pb, 0.001?C0.03 mg g?1 Cd, and 12.6?C140.4 mg g?1 Zn in leaves. The scarce correlations registered between metal concentration in sediment and plant tissues indicate that metal concentrations in plants depend on several factors rather than on sediment concentration only. However, when Cu and Zn sediment concentrations increased, these metal concentrations in tissues also increased in Eichhornia crassipes, Ludwigia helminthorriza, and Polygonum punctatum. These species could be proposed as Cu and Zn phytoremediators. Even though macrophytes are important metal accumulators in wetlands, sediment is the main metal compartment due to the fact that its total mass is greater than the corresponding plant biomass in a given area.  相似文献   

10.
ADSORPTION ON HYDROUS OXIDES I. OXALATE AND BENZOATE ON GOETHITE   总被引：3，自引：0，他引：3  
The adsorption of oxalic acid on synthetic goethite (α-FeOOH) was studied using adsorption isotherms. Infrared spectra were obtained for goethite-oxalate complexes at several points on the isotherms. On a goethite preparation with a phosphate sorption capacity of 200|μmolg?1 the amounts of oxalate strongly adsorbed varied from near zero at pH 8 to about l00μmolg?1 at pH 4 and below. At pH 3.4, the first l00μmolg?1 of oxalic acid added was strongly adsorbed as a binuclear complex (FeOOC–COOFe), replacing two singly-coordinated OH groups by ligand exchange. At higher concentrations a further 200 μrnol g?1 of oxalic acid formed a monodentate complex (FeOOC–COOH) so that more oxalate could be accommodated. Benzoic acid was weakly adsorbed on goethite with one benzoate oxygen replacing one singly-coordinated OH. The other oxygen of the COO group fitted into the goethite surface so that the benzene ring was at a high angle to the (100) face.  相似文献   

11.

Purpose

The choice and timing of microorganisms added to soils for bioremediation is affected by the dominant bioavailable contaminants in the soil. However, changes to the concentration of bioavailable PAHs in soil are not clear, especially when several PAHs coexist. This study investigated the effects of PAH concentration and chemical properties on desorption in meadow brown soil after a 1-year aging period, which could reflect changes of PAH bioavailability during bioremediation.

Materials and methods

Based on the percentage of different molecular weights in a field investigation, high-level contaminated soil (HCS) and low-level contaminated soil (LCS) were prepared by adding phenanthrene (PHE), pyrene (PYR) and benzo(a)pyrene (BaP) to uncontaminated meadow brown soil. The concentrations of HCS and LCS were 250 mg?kg?1 (PHE, PYR, and BaP: 100, 100, and 50 mg?kg?1) and 50 mg?kg?1 (PHE, PYR, and BaP: 20, 20, and 10 mg?kg?1) respectively. The soils were aged for 1 year, after which desorption was induced by means of a XAD-2 adsorption technique over a 96-h period.

Results and discussion

The range of the rapidly desorbing fraction (F rap) for PHE, PYR, and BaP in HCS and LCS was from 1.9 to 27.8 %. In HCS, desorption of PYR was most difficult, and the rate constant of very slow desorption (K vs) of PYR was 8 orders of magnitude lower than that of BaP, which had similar very slow desorbing fractions (49.8 and 50.5 %, respectively). However, in LCS, desorption of PYR was the easiest; the Kvs of PYR was 8–10 orders of magnitude higher than those of PHE and BaP. In HCS, the time scale for release of 50 % of the PAHs was ranked as BaP?>?PYR?>?PHE, while in LCS this was BaP?>?PHE?>?PYR.

Conclusions

The combined effect of PAH concentrations and properties should be taken into account during desorption. The desorption of PAH did not always decrease with increasing molecular weight, and the desorption of four-ring PAHs might be special. These results are useful for screening biodegrading microbes and determining when they should be added to soils based on the dominant contaminants present during different periods, thus improving the efficiency of soil bioremediation.  相似文献   

12.
The colors and color patterns of soils are widely used to infer other soil properties. It is desirable to understand, at least semiquantitatively, the effect various pigments have on soil color. The purpose of this study was to determine how hematite and goethite pigments influence soil color. We prepared simulated soil mixtures consisting of kaolinite and 2.5, 5, 10, 20, 40, 80, 160, 320, 640, and 1000 g kg?1 of pigment (either a synthetic goethite, one of two synthetic hematites, or a mixture of goethite and hematite). We determined the reflectance spectra of the samples, and calculated their colors in the Munsell system. For hematite and goethite pigments mixed with kaolinite, more than half of the change in hue occurred as the Hm/(Hm+Gt) ratio increased from 0 to 0.25, and hue changed relatively little as the Hm/(Hm+Gt) ratio increased from 0.50 to 1.00. Most of the change in color occurred as pigment content increased from 2.5 to 160 g kg?1. Doubling of pigment content from 160 to 320 g kg?1 had very little impact on the colors of the mixtures, while further increases in pigment content between 320 and 1000 g kg?1 caused some changes in color, but less than for the 2.5 to 160 g kg?1 range. A one unit increase in chroma corresponded approximately to a doubling of pigment content in the series 2.5, 5, 10, 20, 40, 80, 160 g kg?1 for the goethite as well as the hematite pigments studied. For one hematite, hues became progressively redder and changed by more than 5 units of hue as pigment content increased from 0.25 to 160 g kg?1.  相似文献   

13.
Benzalkonium chloride (BAC) loaded to montmorillonites (Mt) or organomontmorillonites (OMt) generates a functional material that can be incorporated to several systems (polymers, paints, etc) as a controlled release bactericide. Understanding the BAC adsorption sites on these adsorbents is of high importance to clarify their adsorption/desorption characteristics in aqueous media or other solvents. In this work, a thorough study about the adsorption/desorption properties of Mt and OMt with regards to BAC is presented, in order to evaluate further BAC release with the consequent aquatic environment contamination. In this work, the BAC adsorption on two different sites is demonstrated: the interlayer space and the external surface. Depending on BAC concentration in water, sorption of BAC at Mt occurred in two steps. At adsorbed amount <0.5 mmol g?1, there was an Mt interlayer expansion of 0.49 nm with no change of the external charge. At adsorbed amount >0.5 mmol g?1, there was a new interlayer expansion attaining 0.75 nm and the external charge shifted to positive value. In the case of OMt, the introduction of BAC produced changes in the interlayer structure and in the external surface charge. BAC desorption was strongly dependent on the type of Mt or OMt and extraction solvent, knowledge of which will allow its safe use in environmental friendly technological applications.  相似文献   

14.
The vertical distribution of mercury along a weathering profile derived from a diabase was compared to the main geochemical and mineralogical characteristics of the soil and its parental rock. The sampling site was in a metropolitan area, nearby to an active quarry and relatively close to an industrial park. The samples of a 6-m-deep fresh exposure of the soil profile and also of fresh rock were collected during the dry season. Kaolinite, goethite, hematite, and residual primary minerals were identified in the soil samples. Typically, the concentrations of Hg in the soil are low. Whole samples contained between 1 (rock) and 37 ??g kg?1 Hg, while the?<?63-??m soil fraction had up to 52 ??g kg?1 Hg. The higher values of Hg corresponded to the upper layers of A (0?C10 cm) and B (200?C220 cm) soil horizons. Elemental gains and losses calculated against Zr resulted in the following order: Hg>>Pb?>?Zr?>?LREE?>?Nb?>?HREE?>?Al?>?Ti?>?Fe?>?Cr. Total organic carbon in soil samples varied between 0.2 and 5.1 g dm?3, and correlation with Hg concentrations was moderate. The acid pH (4.2?C5.5) of the soil samples favors the sorption Hg species by predominant secondary phases like goethite and kaolinite. The Hg concentration of the rock is insufficient to explain the large enrichment of Hg along the soil profile, indicating that exogenic Hg, via atmospheric deposition, contributed to the measured Hg concentrations of the soil.  相似文献   

15.
Effluents containing phosphorous as phosphate ions are frequently discharged in freshwater resources contributing to the eutrophication and directly interfering in the biological equilibrium. Clam shell residues and sewage sludge were combined for preparing efficient adsorbents for phosphate removal from aqueous medium. The adsorbents were characterized before and after adsorption testing, and the adsorption equilibrium and kinetics were investigated. Phosphate removal of 89?±?1% was attained for samples prepared with 0.1?< X <?1.0, where X corresponds to sewage sludge/clam shell mass ratio. The analyses of the experimental errors indicated that the phosphorous removal followed the Elovich kinetic model, which describes adsorption in very heterogeneous surfaces. On the other hand, the best modelling was achieved using the Koble–Corrigan isotherm model, which incorporate different aspects of both Langmuir and Freundlich isotherms to represent the equilibrium data. The observed adsorption capacity (21.4 mgP g?1) are comparable or greater to that observed for other adsorbents described in the literature.  相似文献   

16.
Comamonas sp. UVS was able to decolorize Reactive Blue HERD (RBHERD) dye (50 mg L?1) within 6 h under static condition. The maximum dye concentration degraded was 1,200 mg L?1 within 210 h. A numerical simulation with the model gives an optimal value of 35.71?±?0.696 mg dye g?1 cell h?1 for maximum rate (Vmax) and 112.35?±?0.34 mg L?1 for the Michaelis constant (Km). Comamonas sp. UVS has capability of decolorization of RBHERD in the presence of Mg2+, Ca2+, Cd2+, and Zn2+, whereas decolorization was completely inhibited by Cu2+. Metal ions also affected the levels of biotransformation enzymes during decolorization of RBHERD. Comamonas sp. UVS was also able to decolorize textile effluent with significant reduction in COD. The biodegradation of RBHERD dye was monitored by UV–vis spectroscopy, FTIR spectroscopy, and HPLC.  相似文献   

17.
Sludge-derived activated carbons (ACs) were prepared by conventional heating and microwave pyrolysis. The ACs were characterized using several analytical and functional techniques and used for removal of six phenolic compounds from aqueous solutions. The adsorbents exhibited similar features and possessed hydrophobic surfaces. The ACs were assigned mesoporous materials, with specific surface areas of up to 641 and 540 m2 g?1 for CAC-500 and MAC-980, respectively. The preliminary results indicated that phenol removal onto the ACs increased in the order: m-cresol?<?phenol?<?o-cresol?<?2-chrorophenol?<?2-nitrophenol?<?hydroquinone. Hydroquinone exhibited the highest adsorption capacity and was chosen to continue the remaining part of the experimental work—kinetic and isothermal studies. The adsorption kinetic and isotherm data were well described by the Avrami fractionary order and Redlich–Peterson models, respectively. The maximum amounts (Q max) of hydroquinone adsorbed at 25 °C were too high, reaching 1218.3 and 1202.1 mg g?1 for CAC-500 and MAC-980, respectively. The mechanism of adsorption was proposed in this work, and it was suggested that donor–acceptor complex and π–π interactions play major roles in the adsorption process. The adsorbents were also tested on simulated effluents. The two ACs displayed good efficiency for the treatment of industrial simulated effluents.  相似文献   

18.
The capacity of microalgae to accumulate heavy metals has been widely investigated for its potential applications in wastewater (bio)treatment. In this study, the ability of Desmodesmus pleiomorphus (strain L), a wild strain isolated from a polluted environment, to remove Cd from aqueous solutions was studied, by exposing its biomass to several Cd concentrations. Removal from solution reached a maximum of 61.2 mg Cd g?1 biomass by 1 day, at the highest initial supernatant concentration used (i.e., 5.0 mg Cd L?1), with most metal being adsorbed onto the cell surface. Metal removal by D. pleiomorphus (strain ACOI 561), a commercially available ecotype, was also assessed for comparative purposes; a removal of 76.4 mg Cd g?1 biomass was attained by 1 day for the same initial metal concentration. Assays for metal removal using thermally inactivated cells were also performed; the maximum removal extent observed was 47.1 mg Cd g?1 biomass, at the initial concentration of 5 mg Cd L?1. In experiments conducted at various pH values, the highest removal was achieved at pH 4.0. Both microalga strains proved their feasibility as biotechnological tools to remove Cd from aqueous solution.  相似文献   

19.
Abstract

Two experiments were conducted to evaluate the inhibitory effects of 2-chloro-6 (trichloromethyl) pyridine (nitrapyrin) and dicyandiamide on nitrous oxide (N2O), a greenhouse gas, emission from soils amended with ammonium sulfate. In the two experiments, samples of an Andosol and a Gray Lowland soil were kept in glass vessels sealed with a butyl rubber cap and incubated at 25°C. In the first experiment, nitrapyrin (1 µg g?1 dry soil) and dicyandiamide (10 µg g?1 dry soil) were applied to samples of a water-saturated Andosol and a Gray Lowland soil to which ammonium sulfate had been applied at a rate of 0.1 mg N g?1 dry soil. Nitrapyrin decreased N2O emissions from the Andosol and the Gray Lowland soil by 71% and 24%, respectively. Dicyandiamide decreased N2O emissions from the Andosol and Gray Lowland soil by 31% and 18%, respectively. In the second experiment, nitrapyrin (1 µg g?1 dry soil) was applied to samples of an Andosol at 51% water-filled pore space to which ammonium sulfate had been applied at rates of 0.01, 0.1 and 0.5 mg N g?1 dry soil. Nitrapyrin decreased N2O emissions by 62%, 83% and 74%, respectively. Changes in the NH+ 4 and NO? 2 + NO? 3 concentrations in soil showed that nitrapyrin and dicyandiamide slowed down the nitrification process, but did not completely stop the process at any time. The results reveal the potential of nitrification inhibitors to decrease N2O emission from fertilized soil in a wide range of moisture conditions and nitrogen levels.  相似文献   

20.
Abstract

An experiment was conducted to substitute mineral fertilizers with biofertilizers in strawberry to work out the yield, quality of strawberry and soil fertility. A 25% substitution of mineral fertilizer with biofertilizer increased the number of fruits/plant along with improving Juice content (89.55%), Total soluble solids (10.35°B), total sugar (6.69%), ascorbic acid (43.80?mg 100?g?1), anthocyanin content (81.05?mg 100?g?1), total phenol (5.97?mg Gallic acid equiv. g?1), flavonoids (0.12?mg g?1) and antioxidant capacity (2.13?µmol. Trolox equiv. 100?g?1). The available N and K content in post-harvest soils were improved significantly with 75% RDF + Azospirillium @ 2?g plant?1 + PSB @ 2?g plant?1 + topdressing of 25% K treatments (200.10 and 211.70?kg ha?1, respectively). Viable count of soil microorganisms (Bacteria, actinomycetes and fungi) was also estimated maximum (4066, 190 and 11.33?×?104 cfu g?1?dry soil, respectively) with substitution of 25% of mineral fertilizer either with Azotobacter or Azospirillum.  相似文献   

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