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1.
邢光熹  张汉辉  韩勇 《土壤学报》1987,24(3):218-225
本文应用穆斯堡尔谱学方法,研究了在不同pH条件下Fe+++,Fe++与胡敏酸结合的性质。计算机拟合的pH3.057Fe-胡敏酸络合物泥浆的穆斯堡尔谱和参数表明,三对四极双峰(图1,AA',BB',CC')是合理的。在pH3.0 Fe+++以高自旋态存在,它和胡敏酸的结合多于一种环境类型。在pH1.0的57Fe-胡敏酸络合物中,观察到了Fe+++的穆斯堡尔谱信号,但没有Fe++的信号,在这个样品离心分离出的液体部分检测到了加入量的59.7%的铁,表明在pH1.0时相当数量的Fe+++被胡敏酸还原成Fe++,Fe++并不与胡敏酸牢固结合。在30伏电析过的57Fe-胡敏酸络合物样品中(pH2.8)出现了Fe+++,Fe++的穆斯堡尔谱,这一结果指示出,在电析过程中由于57Fe+++-胡敏酸络合物悬浮液pH的降低,一部分Fe+++还原成Fe++,在pH2.8相当数量的Fe++与胡敏酸牢固结合。根据在80K记录的穆斯堡尔谱,在pH1—3的范围出现了磁有序成份,但在室温记录的穆斯堡尔谱没有磁分裂。  相似文献   

2.
Mössbauer specttoscopy has been used to provide information on the effect of pH on the nature of the complexes formed between iron and humic acid. At an initial suspension pH greater than 3 the iron occurs in the ferric form, although it is difficult to assess to what extent it is in combination with organic matter. On lowering the pH, iron is reduced with a considerable proportion of the ferrous iron entering solution, partly as a solvated ion and partly as complex forms. Raising the pH leads to re-oxidation and the precipitation of a considerable proportion of the iron in an inorganic form with Mossbauer parameters similar to those of β-FeOOH. No evidence was obtained for Fe(III) in solution or for Fe(II) in any form at pH values greater than 4.  相似文献   

3.
Abstract

The 5 Msodium hydroxide (NaOH) chemical treatment was applied to the silt and clay fractions of three Chilean fertilized soils derived from volcanic materials (one Ultisol and two Andisols) in order to selectively concentrate iron oxides. The treatment was sequentially applied and results were followed by x‐ray diffraction and Mössbauer spectroscopy. In all samples, dissolution chemical treatment concentrated iron oxides in variable degrees; and both, Mössbauer spectra and x‐ray diffraction patterns were significantly improved after three successive hot NaOH treatments. Best results were obtained for the Ultisol sample which is the oldest soil with the lowest organic matter content. The Mössbauer spectrum after three NaOH treatments of Ultisol silt fraction reveals characteristic features of partially oxidized magnetite, leading to two probability profiles of the hyper‐fine field distribution: One of them due to mixed valence iron (Fe3+/2+) ions in octahedral sites [8=0.59 mm s‐1, 2≥ Q =0.02mm s ‐1, with a maximum hyper‐fine field at Bhf(max)=46.2 tesla]; the other distribution profile encompasses contribution from Fe3+ in tetrahedral sites [δ=0.30 mm s‐1, 2?Q =‐0.04 mm s‐1 , and Bhf(max)=48.2 tesla].  相似文献   

4.
The matrix of iron (hydr)oxides exerts a decisive influence on the character of gleyzation. Upon a high content of iron (hydr)oxides, their reduction radically changes the horizon color from warm to cold hues, which is typical of soils on the Russian Plain. Upon the low content of iron (hydr)oxides, iron reduction takes place in phyllosilicates with minimal changes in the soil color. The cold hue of cryohydromorphic soils in the Kolyma Lowland is controlled by the color of the lithogenic matrix with a low content of iron (hydr)oxides. In this case, the soil color characteristics expressed in the Munsell notation or in the CIE-L*a*b* system are ineffective for diagnostic purposes. The colorimetric methods appear to be more efficient after the soil pretreatment with hydrogen peroxide, as the gleyed horizons turn green, while the nongleyed (and not overmoistened) horizons turn red. Physical methods (Mössbauer spectroscopy and magnetic susceptibility measurements) are more efficient for characterizing the properties of iron compounds in cryohydromorphic soils as compared with the methods of chemical extraction. Mössbauer spectroscopy proved to be highly efficient, as the iron oxidation index Fe3+/(Fe2++Fe3+) decreases in the gleyed horizons. Chemical reagents (Tamm’s and Mehra-Jackson’s reagents) dissolve Fe-phyllosilicates and are not selective in soils with a low content of iron (hydr)oxides.  相似文献   

5.
Different particle-size fractions of soil clays from the semi arid north and the humid tropical south of Cameroon have been characterized with reference to their chemical composition, clay mineralogy and kaolinite crystallinity (Hinckley indices). Selected samples were also examined by Mössbauer spectroscopy. Hinckley indices of kaolinites, which were a major component of the coarse clays, varied considerably (< 0.1 - 0.69) and differed significantly as a function of the geographic and landscape positions of the soil profiles. The Hinckley indices averaged 0.31 in soils from southern Cameroon and 0.30 and 0.07 in soils from high and low landscape positions in northern Cameroon, respectively. Kaolinite crystallinity is therefore considered to vary as a function of transport and/or depositional environment of the kaolinite-containing material. Mössbauer spectra showed that kaolinite-dominated Vertisol coarse clays contained higher relative amounts of Fe2+ than the corresponding fine clay, which is dominated by smectite. It is conceivable that the Fe2+ content of the kaolinite reflects the redox environment of the samples.  相似文献   

6.
The decomposition of nitrite was studied in the presence of (1) different amounts of ferrous iron and (2) an amorphous and a crystalline (haematite) iron product at different pH and Eh conditions. It was found that ferrous iron positively influenced the nitrite decomposition. Even at pH 6, where self-decomposition is excluded, some nitrite was decomposed. It was shown that at all studied pH values the second order decomposition rate increased as the amount of ferrous iron increased. From the calculation of the activation energy it was found that the dependence of the rate constant on temperature increased when the medium was more acid, or when the amount of Fe2+ increased at the same pH. The nitrite half-life was longest at pH 6, 25°C and 200 mg Fe2+ l?1; it was shortest at pH 4, 30°C and 800 mg Fe2+ l?1. The experiments with Fe2+ derived from solid iron compounds showed that all conditions favouring a high amount of ferrous iron in solution, such as low redox potential, low pH, amorphous or less crystalline material, enhanced nitrite decomposition.  相似文献   

7.
Mössbauer spectra of three nontronite samples (Garfield H33a and SWa-1 from Washington State, U.S.A., and a sample from Hundsangen, Germany), taken between room temperature and 4.2 K in the velocity range ± 10.5 mm/s, showed between 2.9 and 13% of the total iron to be bound in goethite and not in the nontronite structure. This extraneous iron limits the utility of room temperature spectra for the assignment of structural iron sites in these samples. An adequately good distinction of the contributions of goethite and nontronite was possible in Mössbauer spectra taken at 77 K. The spectral components arising from iron in the nontronite octahedral sheets could be fitted with distributions of quadrupole-split doublets. These distributions indicate the existence of quasi-continuous octahedral site variations rather than two discrete (cis and trans) sites, and thus favour a structural model in which all octahedral iron is in cis coordination.  相似文献   

8.
Mössbauer and ESR spectroscopy have shown that the iron extracted from the Bh horizons of an iron humus podzol and an iron podzol by EDTA at pH 9.1 is predominantly in the form of complexes * 1 The use of the word ‘complex’ in this paper in the context of polymeric iron species and organic matter is not intended to imply any single specific type of complex, such as exists in Fe(II1) EDTA, for example, but to embrace many possible modes of association including salt formation, direct coordination, Van der Waal's adsorption, and electrostatic attraction.
of polymeric Fe(III) hydroxide and oxide with organic matter (O.M.). Small amounts of monomeric Fe(III)-O.M. and Fe(III)-EDTA complexes also occur. In contrast EDTA at pH 7 extracts iron from these podzols predominantly in the form of iron-EDTA complexes. Some monomeric Fe(III)-O.M. complex also occurs in a pH 9.1 NH4 OH extract of these horizons and in a pH 9.1 EDTA extract of the B3 horizon of a peaty podzol. Dialysis experiments show that the particle dimensions of the polymeric hydroxy Fe(III)-O.M. complex, which accounts for about 66% of the Fe extracted from the iron humus podzol and about 36% of that from the iron podzol, are greater than 2.4 nm. The thermal behaviour of the Mössbauer peaks indicated that the size of the iron cores was of the order of 5 nm, thus suggesting that the complex probably consists of hydroxyiron cores surrounded by large organic molecules. Results from XRD and IR suggest that these hydroxyiron cores may have structural organizations similar to those of goethite and ferrihydrite. The relationship between these forms of iron in the extracts and those in the soil is briefly discussed.  相似文献   

9.
At low concentrations (up to 50 mg/l) humic acid enhances cell elongation in excised pea root segments, but at higher concentrations it is inhibitory. At concentrations stimulating cell elongation humic acid has no effect on protein metabolism but does inhibit the formation of cell-wall bound hydroxyproline from proline. Humic acid does not stimulate cell elongation or inhibit the formation of cell-wall bound hydroxyproline in the presence of ferrous iron. Results similar to those of humic acid were obtained using the iron chelator αα'-dipyridyl, but γγ'-dipyridyl. which does not chelate iron. was without effect on cell elongation.The cessation of cell elongation corresponds to the time at which there is a substantial increase in cellwall bound hydroxyproline, this latter process requiring ferrous iron. Thus humic acid may enhance growth by virtue of its ability to complex ferrous iron within the plant tissues.  相似文献   

10.
The microstructural stability of soils of different geneses (steppe soils, tropical soils, and subtropical soils) developed from marine clay, loess, and weathering crusts was studied by the method of successive treatments with chemical reagents destroying the particular clay-aggregating components. The following dispersing agents were used: (1) H2O (pH 5.5), (2) 0.1 N NaCl (pH 6), (3) 0.002% Na2CO3 (pH 8.7), (4) 0.1 N NaOH (pH 11.5), (5) the Tamm reagent (pH 3.2), and (6) 0.1 N NaOH (pH 11.5). The properties of the clay subfractions obtained in the course of these treatments were studied by a set of analytical methods, including X-ray diffractometry, Mössbauer spectroscopy, and magnetic measurements. It was shown that soil microaggregates are formed under the impact of a number of physicochemical processes; the content and properties of inorganic components (clay minerals in soils with a high CEC and iron oxides in soils with a low CEC) are the controlling factors. The structure of the parent materials is transformed to different degrees to form the soil structure. For example, autonomous nondifferentiated soils inherit, to some extent, the specific microorganization of the parent material. At the same time, the redistribution of substances in the soil profile and in the landscape may exert a substantial influence on the soil structure and microstructure. This is particularly true for autonomous differentiated soils, turbated soils, accumulative soils, polylithogenic soils, and polygenetic soils. The properties of the obtained subfractions of the clay (the mineralogical composition, the Fe2+/(Fe2+ + Fe3+) ratio, the magnetic susceptibility, and the Cha/Cfa ratio) attest to the spatial heterogeneity of the composition and properties of the mineral and organic aggregated compounds in soils.  相似文献   

11.
Synthethic goethite specimens have been prepared by a variety of experimental methods, and it has been possible to incorporate large quantities of Al ( 30 mol %) into the structure. A range of particle sizes also obtained and these were dependent upon both experimental conditions and the extent of aluminium substitution. Mössbauer spectra have been recorded for a large number of samples and show that high levels of A1-substitution combined with small particle sizes have a dramatic effect on the magnetic properties of the mineral. The application of Mössbauer spectroscopy to the identification of secondary iron oxide phases in soils is thus complicated by aluminium substitution and some of the difficulties are discussed.  相似文献   

12.
Summary The stability constants (log K) of Fe2+ chelates were determined on the basis of the shift in peak potential during the reduction of Fe2+ by a consortium of soluble ligands from incubated soils. Log K values ranged from 2.6 to 4.5. On average a change in pH of 1 unit induced a change in log K of 0.92 units. Aeration of the anaerobic decomposition products increased log K. The log K for Fe2+ chelates was about 0.8 units larger than that for Mn2+ chelates. It is considered that the chelation of ferrous iron plays an important role in the mobility and availability of iron to plants.  相似文献   

13.
Humic acid (HA) extracted from a Eustis loamy sand (Psammentic Paleudult, Red Yellow Podzolic soil) was flocculated by titration with Al3+-, Fe3+-, Cu2+-, Zn2+-, Mn2+-, Ba2+-, Ca2+-, and Mn2+-chloride solutions, respectively, to determine possible development of metal-HA complexes, as reported by Flaig et al. (1975), and Tiurin and Kononova (1962). Titration was conducted with HA solutions with an initial pH 11.5 or 7.0. The results indicated that the cations used, except Mg2+, yielded insoluble complexes with HA, irrespective of initial pH. After titration, the pH of the metal-HA flocs was 6.0–7.0, which was expected in view of the presence of cation exchange and buffering capacity of HA compounds. More complex formation through electrovalent and covalent bonding by COO? and phenolic OH groups of the HA molecule was only attained by the use of HA solutions with pH 11.5. On the other hand, less complex formation occurred by the use of HA solutions with an initial pH 7.0, through electrovalent bonding by COO? groups. Differential thermal analysis (d.t.a.) curves of HA showed shifts in temperatures of the main decomposition peak as a result of flocculation with the different metals. Based on the type of the cations involved, the metal-humic acid flocs could be listed in the following decreasing order of thermal stability: Al3+ = Zn2+ = Mg2+ ≥ HA > Ca2+ > Ba2+ > Fe3+ > Cu2+ > Mn2+. A systematic relationship could not be found indicating that trivalent ions resulted in the formation of thermally less stable metal-humic acid flocs than divalent ions, as has been reported for HA-metal complexes. Physical mixtures of HA and metal hydroxides exhibited d.t.a. features resembling those of original (nontreated) HA, but not those of the HA-metal flocs.Infrared spectroscopy revealed increased absorption for COO? vibrations at 1620 and 1400cm?1 in spectrograms of metal-HA flocs compared to that of original humic acid, a phenomenon explained by many authors to be caused by bonding of the metal ions in hydrated form to the carboxyl or phenolic hydroxyl groups or both of the humic acid molecule. HA-flocs formed from solutions with an initial pH 11.5 had identical i.r. spectra compared with those formed from solutions with an initial pH 7.0.  相似文献   

14.
-Humic acid (AH) and invertase (I) may be complexed with one of the following cations Ca2+, Co2+, Cu2+, Mg2+, Mn2+, Al3+ or Fe3+ in order to study their catalytic activity and longevity. Provided that enough cations are supplied there is an immediate, almost total flocculation with Cu2+, Al3+ and Fe3+, or a slow flocculation with Ca2+, Co2+ and Mn2+ or no flocculation at all with Mg2+, depending on the reactivity between organic matter and cation. The six kinds of complexes have very different enzymatic activities in magnitude and longevity.No correlation was found between enzymatic activity and the atomic weight and valency of the cation used to prepare the complex. There is a pH at which flocs occur that is closely related to the pH of the metal chloride and to the affinity of each cation for precipitate; this pH value largely determines the structure of the humic material and consequently the catalytic activity of the enzymatic complex produced. For Cu2+, Al3+ and Fe3+ complexes, the pH values are low, between 1.7 and 3.2 and correspond to high conversion rates if the AH-I-cation reaction time is short; in cases where the reaction time is more protracted, enzyme molecules bound to the outer surface of the micellae are denatured by these very low pH values and the complexes irreversibly lose much of their activity. For Ca2+, Co2+ and Mn2+, the pH values lie between 4.30 and 5.65 and correspond to nearly ten times lower enzymatic activities; here, however, a prolonged reaction enhances activity. For Mg2+, the pH is 6.25–6.45; for this value, the humic material remains highly dispersed in buffer and the complex AHMg-I cannot be separated.The possibility of a relation between the number of enzyme molecules retained in complexes and the cationic radii on the one hand, and between the longevity of the complexes and the bound-state of humic acid-flocculating cation, on the other hand, is suggested.  相似文献   

15.
A 9-month-long continuous flow column study was carried out to investigate Cr(VI) removal by Fe0 with the presence of humic acid. The study focused on the influences of humic acid promoted dissolved iron release and humic acid aggregation in Fe0 columns receiving synthetic Cr(VI) contaminated groundwater containing various components such as bicarbonate and Ca. The effects of humic acid varied significantly depending on the presence of Ca. In Ca-free columns, the presence of humic acid promoted the release of dissolved iron in the forms of soluble Fe-humic acid complexes and stabilized fine Fe (hydr)oxide colloids. As a result, the precipitation of iron corrosion products was suppressed and the accumulation of secondary minerals on Fe0 surfaces was diminished, and a slight increase in Cr(VI) removal capacity by 18% was record compared with that of humic acid-free column. In contrast, in the presence of Ca, as evidenced by the SEM and FTIR results, humic acid greatly co-aggregated with Fe (hydr)oxides and deposited on Fe0 surfaces. This largely inhibited electron transfer from Fe0 surfaces to Cr(VI) and reduced the drainable porosity of the Fe0 matrix, resulting in a significant decrease in Cr(VI) removal capacity of Fe0. The Cr(VI) removal capacity was decreased by 24.4% and 42.7% in humic acid and Ca receiving columns, with and without bicarbonate respectively, compared with that of Ca and humic acid-free column. This study yields new considerations for the performance prediction and design of Fe0 PRBs in the environments rich in natural organic matter (NOM).  相似文献   

16.
Sorption of primisulfuron on soil, and inorganic and organic soil colloids   总被引：2，自引：0，他引：2  
Inorganic and organic soil colloids are responsible for the sorption of many pesticides. We studied the sorption of the herbicide primisulfuron [methyl 2 N‐[[[[[4,6‐bis(difluoromethoxy)‐2‐pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzoate] on Fe3+‐, Al3+‐, Ca2+‐ and Na+‐exchanged montmorillonite, soil organic matter (H+‐ and Ca2+‐saturated), amorphous iron oxide, and three soils in aqueous media. The sorption on soils was negatively correlated with pH. Ca2+‐ and Na+‐exchanged montmorillonites are ineffective in the sorption of primisulfuron. The sorption on Fe3+‐ and Al3+‐exchanged montmorillonite is rapid and follows the Freundlich equation. Fourier transform infrared (FT‐IR) and X‐ray powder diffraction studies of the Fe3+‐ and Al3+‐montmorillonite samples after the interaction with primisulfuron in chloroform solution suggest that primisulfuron is adsorbed and degraded in the interlayer. Humic acid is more effective in the sorption than is Ca humate, suggesting that the pH of the suspension (3.5 for humic acid and 6.0 for Ca humate) has a strong influence on the sorption of primisulfuron. Experiments on amorphous iron oxide indicate similar pH dependence. Infrared spectra indicate that the protonation of the pyrimidine nitrogen moiety of herbicide and subsequent hydrogen bonding with the surface hydroxyls of Fe oxide is the mechanism acting in the primisulfuron sorption.  相似文献   

17.
Soils of former coking plant sites are frequently contaminated with cyanide, which mainly occurs as the pigment Berlin blue, FeIII4 [FeIICN)6]3, and soluble iron cyanide complexes, Fe(CN)63-/4?. Berlin blue is only slightly soluble under acidic conditions. The cyanide mobility in a strongly acid soil (pH about 3) of such a site was studied by assessing the distribution of cyanides in the soil and sediment and by conducting batch experiments at different pH levels. The soil is based on a disposal layer (0–32 cm) overlying sandy loess (32–145 cm) overlying glaciofluvial sand (145–250 cm) overlying marlstone (250–500 cm). Highest cyanide concentrations were found in the disposal layer (62–2865 mg CN? kg?1), medium concentrations in the sandy loess (16–29 mg CN? kg?1), concentrations of about 100 mg CN? kg?1 in the glaciofluvial sand and lowest concentrations in the marlstone (0.22–0.49 mg CN?1 kg?1). The surfaces of macropores, which occur in the sandy loess and finish in the glaciofluvial sand, are dark-blue dyed and have much higher cyanide concentrations than the surrounding bulk soil. Thus, the accumulation of cyanides in the sand layer may partly be the result of macropore flow. Batch experiments show a strong pH dependence of the solubility of cyanide in the soil as well as of Berlin blue which was found by Mössbauer spectroscopy to be the dominating or sole iron cyanide. The time necessary to transport the cyanides solely as hexacyanoferrate into the undisturbed horizons is estimated to 1000 yr. However, because Berlin blue is known to form colloids, we discuss the possibility of cyanide transport as colloid not requiring dissolution and reprecipitation. We postulate that colloidal Berlin blue transported by macropore flow is responsible for the high mobility of cyanides in this acid soil.  相似文献   

18.
Fulvic acids have been isolated from a sandy loam (Countesswells series) and a clay soil (Tipperty series) and the products of their reaction with different amounts of iron over a range of pH from 0.5 to 11 analyzed by Mössbauer spectroscopy. Three distinct types of spectral component were detected at 77 K, a sextet from magnetically dilute Fe(III) and doublets from Fe(II) and Fe(III), the last arising from both organic complexes and poorly crystalline oxide species. In iron-fulvic acid mixtures the proportion of iron as Fe(II) increased as the pH was lowered from 5 to 1 by the addition of hydrochloric or nitric acid at all Fe to fulvic acid ratios (1:5 to 1:500). When the pH was lowered below 1 the amounts of Fe(II) decreased with the lower Fe to fulvic acid ratios, but increased with the higher ratios. The amounts of the Fe(III) component contributing to a doublet signal decreased with decreasing Fe:fulvic acid ratios. At low iron concentrations the iron appears to be strongly bound to the fulvic acid, but when the iron content is of the order of 1–2% uncomplexed Fe(III) species can be present. At pH > 2 these are hydrolysed ions which form poorly-crystalline oxides at higher pH. This was confirmed by analysis of spectra at 4.2 K. At pH < 2 free ions are present in solution. In solutions with high fulvic acid contents (greater than 100-fold excess) the reactions with iron are completely reversible, but in solutions with a lower proportion of fulvic acid to iron, where free ions are present, there is a lack of reversibility.  相似文献   

19.
Theoretical Considerations of the reductive dissolution of iron(III) oxides At the case of equilibrium, the extent of reductive dissolution of iron(III) oxides can be obtained by the Nernst equation. At a given pH, the maximum Fe2+ concentration depends on the standard potential Eo of the system, which decreases with increasing stability of the oxide. Crystal imperfections as well as increasing surface area lead to an increase of the equilibrium Fe2+ concentration, whereas the influence of ionic replacement cannot be determined in general. The formation of stable Fe2+ complexes or of solid Fe2+ compounds results in a higher extent of reduction. From theoretical calculations it is concluded, that, for the bacterial reduction of iron oxides, the electron transfer between donor and Fe(III) precedes the protolytic dissolution of the oxide.  相似文献   

20.
Abstract

When a soil is flooded, iron (Fe) reduction and methane (CH4) production occurred in sequence as predicted by thermodynamics. The dissolution and precipitation of Fe reflected both soil pH and soil redox potential (Eh). The objective of our experiment was to determine both CH4 production and Fe reduction as measured by Fe in solution in a flooded paddy soil over a wide range of closely controlled pH and Eh conditions. The greatest release of CH4 gas occurred at neutral soil pH in combination with low soil redox potential (‐250 mV). Production of CH4 decreased when soil pH was lowered in combination with an increase in the soil redox potential above ‐250 mV. Highest concentration of ferrous‐iron (Fe2+) under reducing conditions occurred when soil pH was lowered. Thus Fe reduction influenced CH4 formation in the flooded paddy soil. Results indicated that CH4 production was inhibited by the process of ferric‐iron (Fe3+) reduction.  相似文献   

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