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1.
Organic matter from an arable soil derived from base rich parent material was extracted by alkali and fractionated on the basis of solubility in 0.1 N HCl, hot water and hot 6 N HCl and by selective adsorption on charcoal. The distribution of associated metals was determined and Cu had the largest proportion, 15%, associated with the organic matter. Moderate proportions of the total Al, Co, Ni, and V (3–8%) but only small amounts (?1%) of the Mn, Fe, Ti, Cr, Ba and Sr were extracted from the soil by alkali. The Fe and Ti were concentrated mainly in the humic fraction whereas Mn and V were both found largely in the fulvic acid.Electron paramagnetic resonance spectra of the various fractions were examined and attempts made to relate the spectra to the forms of some of the metals present. In the humic acid fraction Cu was present partly as a copper porphyrin-type complex but in the fulvic acid it was in some other complexed form. VO2+ occurred in complexed forms in the fulvic acid which were more covalent than VO2+ humic acid complexes, whereas the Mn2+ components of the humic and fulvic acids all had a high degree of ionicity.  相似文献   

2.
The IR and 1H-NMR spectra of fulvic acids (FA) are discussed. The FA, extracted by traditional methods, were fractionated on the basis of molecular weight (m.w.). Three fractions were obtained labelled FA I (m.w. > ～ 2000), FA II (m.w. > ～ 12000) and FA III (～2000 < m.w. < ～ 12000). Fraction FA II was methylated with CH3I-Ag2O. The 1H-NMR spectra of unmethylated FA fractions show some signals common to all three fractions and some differences in the 3–5 ppm range due to the resonances of OCH3 and O-CH2 groups. The proton spectrum of the methylated fraction shows absorption areas for OCH3 groups of phenols and carboxyls. The results confirm that NMR spectroscopy is a convenient technique which can contribute to defining the chemical structure of humic substances.  相似文献   

3.
《Applied Geochemistry》1995,10(2):197-205
The adsorption of Zn (total concentration 10−6 M) to colloidal quartz, hydrargillite and goethite (50, 300 and 70 mg/l, respectively) was studied by a batch technique at a constant ionic strength (0.01 M) but with variation of pH (3–10) and fulvic acid (FA) concentration (0, 2 or 20 mg/l). The adsorption had similar pH-dependence in all systems in the absence of FA giving a pH50 (pH of 50% adsorption) of 7.6 under these conditions. The presence of the FA reduced the overall adsorption to quartz (pH50 of 7.9 at 2 mg FA/I and 9.3 at 20 mg/1) and shifted the adsorption curves downwards (pH50 of 6.8) in the hydrargillite and goethite systems at 2 mg FA/l. At 20 mg FA/l, the adsorption in the two latter systems was increased at pH <6.5 and reduced at pH >6.5. The results reflect the affinity of the surfaces for FA as well as the formation of Zn–FA complexes (in solution and on solid surfaces).  相似文献   

4.
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5.
Electron paramagnetic spectra of humic acid and various fractions of fulvic acid from a deep peat soil were studied and related to some of the metals present. In fulvic acid, VO2+ occurred in complexed form. The Mn2+ components all had a high degree of ionicity. In the humic acid fraction Cu2+ was present as a copper porphyrin-type complex.  相似文献   

6.
The interfacial structures of the basal surface of muscovite mica in solutions containing (1) 5 × 10−3 m BaCl2, (2) 500 ppm Elliott Soil Fulvic Acid I (ESFA I), (3) 100 ppm Elliott Soil Fulvic Acid II (ESFA II), (4) 100 ppm Pahokee Peat Fulvic Acid I (PPFA), and (5) 5 × 10−3 m BaCl2 and 100 ppm ESFA II were obtained with high resolution in-situ X-ray reflectivity. The derived electron-density profile in BaCl2 shows two sharp peaks near the mica surface at 1.98(2) and 3.02(4) Å corresponding to the heights of a mixture of Ba2+ ions and water molecules adsorbed in ditrigonal cavities and water molecules coordinated to the Ba2+ ions, respectively. This pattern indicates that most Ba2+ ions are adsorbed on the mica surface as inner-sphere complexes in a partially hydrated form. The amount of Ba2+ ions in the ditrigonal cavities compensates more than 90% of the layer charge of the mica surface. The electron-density profiles of the fulvic acids (FAs) adsorbed on the mica surface, in the absence of Ba2+, had overall thicknesses of 4.9-10.8 Å and consisted of one broad taller peak near the surface (likely hydrophobic and positively-charged groups) followed by a broad humped pattern (possibly containing negatively-charged functional groups). The total interfacial electron density and thickness of the FA layer increased as the solution FA concentration increased. The sorbed peat FA which has higher ash content showed a higher average electron density than the sorbed soil FA. When the muscovite reacted with a pre-mixed BaCl2-ESFA II solution, the positions of the two peaks nearest the surface matched those in the BaCl2 solution. However, the occupancy of the second peak decreased by about 30% implying that the hydration shell of surface-adsorbed Ba2+ was partially substituted by FA. The two surface peaks were followed by a broad less electron-dense layer suggesting a sorption mechanism in which Ba2+ acts dominantly as a bridging cation between the mica surface and FA. When the muscovite reacted first with FA and subsequently with BaCl2, more Ba2+ could be adsorbed on the FA-coated mica surface. The peak closest to the mica included Ba2+ ions adsorbed directly on the mica in an amount similar to that in the BaCl2 solution but more broadly distributed. A second peak observed within the FA layer suggests that the FA coating provides additional sites for Ba2+ sorption. The results indicate that enhanced uptake of heavy metals can occur when an organic coating already exists on a mineral surface.  相似文献   

7.
《Applied Geochemistry》2000,15(2):133-139
The sorption of Yb3+, UO2+2, Zn2+, I− and SeO2−3 onto Al2O3, Fe2O3 and SiO2 were determined by a batch technique in the presence and absence of fulvic acids. The effects of fulvic acid on sorption were compared. The existing general consensus, that humic substances tend to enhance metal cation sorption at low pH, reduce metal cation sorption at high pH and reduce inorganic anion sorption between pH values 3 to 10, was generally shown to be true. However, in this work many exceptions to the general consensus were found. The study indicated that the effect of humic substances on sorption of inorganic cations or anions depends not only on pH, but also on the nature of the oxide, the nature of humic substance, fractionation of the humic substance by sorption, the relative strength of complexes of both soluble and sorbed humic substances, the extent of surface coverage by humic substance, the initial concentration of humic substance and the inorganic electrolyte composition.  相似文献   

8.
1H NMR spectra of humic (HA) and fulvic (FA) acids and their oxidative degradation products are reported. The HA shows the presence of -(CH2)n - CH3 (n > 6) chemical fragments belonging to n-alkanes and/or n-fatty acids physically adsorbed onto the macromolecule structure. These fragments are absent in the FA fraction. Both humic fractions reveal the presence of similar amounts of aromatic protons which partly undergo exchange phenomena. The importance of this experimental observation is discussed. Oxidative degradation seems to cause partial cleavage of aromatic rings, more pronounced in the FA than in the HA. The degraded FA shows a higher total acidity and a higher phenolic OH content than the degraded HA. Both degraded fractions display some sharp singlet signals at 1.9 and 3.9 ppm arising from protons belonging to repetitive chemical fragments probably formed during the oxidation reaction. Tentative assignments of these signals are given. A general analysis of the HA and FA degraded spectra seems to indicate that the chemical fragments which undergo peracetic oxidation are substantially similar. The extent of oxidation of the two humic fractions is different. The HA degradation products reveal the presence of oligomeric structures, whereas the degraded FA appears less resistant to the oxidizing agent.  相似文献   

9.
The interaction of Cr(III) with humus acids [fulvic (FA) and humic (HA) acids] was studied in the systems Cr(III)-FA, Cr(III)-HA, and Cr(III)-FA-HA. Chromium(III) reacts with FA extracted from the headwaters of the Moscow River and from the Krapivenka River (a tributary of Lake Seliger) to form a highly soluble high-molecular-weight Cr(III)-hydroxofulvate complexes with \(\bar \beta _{11} \) = 1.93 × 106 and 5.70 × 106, respectively. Humic acids extracted from peat in the Tver area and the sapropel of Lake Seliger behave as complexing sorbents with conditional affinity constants logβ = 3.78 and 3.23 for Cr(III) sorption at HA sites in the peat and sapropel, respectively. In the three-component system Cr(III)-FA-HA, the Cr(III) distribution coefficient between solution and precipitate is controlled by the pH value and FA content in the solution and decreases by 1–1.5 orders of magnitude with increasing fulvic acid content.  相似文献   

10.
Pb2+, like Cu2+, forms strong complexes with fulvic acids (Cd2+-fulvate complexes are much weaker), but Pb-fulvate precipitates at a much lower mole ratio of metal ion to fulvic acid than either Cu-fulvate or Cd-fulvate does. Physical association of Pb2+ with Pb-fulvate solids as well as complexation by sites still available in the precipitates probably causes the increased removal of free Pb2+ from solution after precipitation begins.  相似文献   

11.
《Organic Geochemistry》1999,30(8):901-909
Deuterium nuclear magnetic resonance spectroscopy (2H-NMR) spin–lattice relaxation (T1) experiments were used to measure noncovalent interactions between deuterated monoaromatic compounds (phenol-d5, pyridine-d5, benzene-d6) and fulvic acids isolated from the Suwannee River and Big Soda Lake. Noncovalent interactions, in aqueous solution, were examined as a function of monoaromatic hydrocarbon functional groups, fulvic acid concentration and identity, and solution pH. Phenol did not exhibit noncovalent interactions with either fulvic acid at any pH. Pyridine, in a pH range from 3 to 8, interacted with Suwannee River fulvic acid, forming a bond involving the lone pair of electrons on nitrogen. Conversely, no interactions were observed between pyridine and Big Soda Lake fulvic acid; the difference in noncovalent interactions is attributed to the structural and chemical differences of the two fulvic acids. The translational and rotational molecular motion of benzene increased in the presence of both fulvic acids, indicating that in aqueous solution, fulvic acids solubilize benzene rather than forming discrete bonds as with pyridine. The results of this study demonstrate that monoaromatic functional groups, solution pH, and identity and concentration of fulvic acid can influence the type and degree of noncovalent interactions with dissolved organic matter.  相似文献   

12.
Sorption of Ni2+ on Na-rectorite as a function of contact time, temperature, pH and fulvic acid (FA)/humic acid (HA) was studied under ambient conditions. A pseudo-second-order rate equation was used to simulate the kinetic sorption. The removal of Ni2+ increased with increasing pH. The presence of FA/HA enhanced the sorption of Ni2+ at low pH values, whereas no drastic effect of FA/HA on Ni2+ uptake to rectorite was found at high pH values. The diffuse layer model (DLM) fitted the experimental data of Ni2+ sorption in the absence and presence of FA/HA very well with the aid of FITEQL 3.2. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Ni2+ at different temperatures. The thermodynamic data (ΔH0, ΔS0, ΔG0) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of Ni2+ on rectorite was spontaneous and endothermic. The sorption and species of Ni2+ on rectorite in the presence and absence of FA/HA was also investigated and characterized by XPS. The spectroscopic analysis indicated no drastic structural changes of Na-rectorite and the sorption of Ni2+ mainly occurred on the surface and at the edge position of Na-rectorite.  相似文献   

13.
Molecular-scale distributions of Sr2+ and fulvic acid (FA) adsorbed on the muscovite (0 0 1) surface were investigated using in situ specular X-ray reflectivity (XR) and resonant anomalous X-ray reflectivity (RAXR). The total amount of Sr2+ adsorbed from a 1 × 10−2 mol/kg SrCl2 and 100 mg/kg Elliott Soil Fulvic Acid II (ESFA II) solution at pH 5.5 compensated 81 ± 5% of the muscovite surface charge, less than previously measured (118 ± 5%) in an ESFA II-free solution with the same Sr concentration and pH. Inner-sphere (IS) and outer-sphere (OS) Sr2+ constituted 87% of the total adsorbed species in IS:OS proportions of 19:81 compared to 42:58 in the solution without FA, suggesting that adsorbed FA competes with the IS Sr2+ for surface sites. The coverage of both IS and OS Sr2+ decreased even more in a pH 3.5 solution containing the same concentration of FA and 0.5 × 10−2 mol/kg Sr(NO3)2, whereas a significant amount of Sr2+ accumulated farther from the surface in the FA layer. The amount of Sr2+ incorporated in the ∼10 Å thick FA layer decreased by 79% with decreasing FA concentration (100 → 1 mg/kg) and increasing Sr2+ concentration (0.5 × 10−2 → 1 × 10−2 mol/kg) and pH (3.5 → 3.6). These results indicate not only that adsorbed FA molecules (and perhaps also H3O+) displace Sr2+ near the muscovite surface, but also that the sorbed FA film provides binding sites for additional Sr2+ away from the surface. When a muscovite crystal pre-coated with FA after reaction in a 100 mg/kg ESFA II solution for 50 h was subsequently reacted with a 0.5 × 10−2 mol/kg Sr(NO3)2 and 100 mg/kg ESFA II solution at pH 3.7, a significant fraction of Sr2+ was distributed in the outer part of the FA film similar to that observed on fresh muscovite reacted at pH 3.5 with a pre-mixed Sr-FA solution at the same concentrations. However, this Sr2+ sorbed in the pre-adsorbed organic film was more widely distributed and had a lower coverage, suggesting that pre-sorbed FA may undergo fractionation and/or conformational changes that diminish its capacity, and that of the muscovite (0 0 1) surface, for adsorbing the aqueous Sr cation.  相似文献   

14.
The technique of competitive ligand-exchange/anodic stripping voltammetry (CLE-SV) was used to investigate effects of pH and Ca concentration on cadmium complexation by fulvic acid (FA), as well as Cd speciation in two different freshwaters, a hardwater Lake Greifen and a softwater River Wyre. Binding of Cd to Suwannee river FA (10 mg/l) was determined at different pH (7–8.5) and in the presence of various concentration of Ca2+ (0–2 mmol/l). The results from one-ligand discrete models were compared to simulations by the WHAM VI model. In Lake Greifen, the determined dissolved [Cd2+] ranged from 10−13 to 10−12 mol/l, and the conditional stability constant with natural ligands was log K CdL about 9.5–10.5 (pH 8.6–8.8) with ligand concentrations of 1.2–7.8 × 10−6 mol/g C. In the softwater River Wyre, dissolved [Cd2+] ranged from 4 × 10−12 to 1 × 10−11 mol/l, and the ligands were weaker (log K CdL 8.9–9.8, pH 8.0) with lower ligand concentrations (0.9–2.3 × 10−6 mol/g C). The titration curves of FA samples were close to the simulated curves by the WHAM VI model at pH 8.0–8.5, but deviated more from the model at lower pH, indicating that the results determined with CLE-SV for Cd-FA complexation are relevant to the data base in the model. Calculation of the Ca competition for Cd binding by FA showed a competition effect of similar strength as the measured one, but indicated a systematic difference between measured and modeled data at pH 7.5. Using the WHAM model for comparison with FA, the complexation of Cd by the River Wyre ligands was close to that of FA, whereas stronger complexation was observed in the Lake Greifen water. These differences may originate from different ligand composition in the lake and the river.  相似文献   

15.
Potentiometric titrations were used to measure conditional stability constants of UO22+-fulvic acid and UO22+-humic acid complexes. Both 2:1 and 1:1 COO-:UO22+ binding were observed. With decreasing metal concentration (2.5·10−4-6.25·10−5 M) increasing amounts of UO22+ were in the form of 1:1 humate complexes and 2:1 fulvate complexes. Despite the high nitrogen content and the low acidic OH group content, the successive stability constant values were similar to those determined for divalent cations associated with fulvic and humic compounds isolated from soils. Stability constant values increase simultaneously with increasing ionization of the humic (or fulvic) acid polyelectrolytes and with decreasing metal concentration.  相似文献   

16.
The following organic radicals were identified by EPR spectroscopy in apatite from marine phosphorites (granular, nodular, shelly, and microcrystalline), supergene phosphorites (from ocean islands only), and modern and fossil biological materials (human dental enamel, fossil shark teeth, and pathogenic cardioliths): ?H3, ?H2-R, HO?HR,(CH3)2-?R,3?org, PO 3 2? , P(OR)3, and perinaphteenyl. Each textural and petrographic type of apatite corresponds to a specific model of organic radicals, which correlates with the type of organic matter (sapropelic, humic, guano, or collagen). The latter is controlled by the conditions of mineral formation, including climatic ones, and postdiagenetic (catagenetic) processes. A relationship was established between the EPR spectra of observed organic radicals and the valence state and structural position of impurity ions: (1) vanadium: V4+ (VO2+) in the Ca2+ II site or V5+ (VO4)3? ?? (PO4)3? and (2) uranium: U4+(UO2) in the Ca2+ II site or U6+ chemisorbed on the surface as UO 2 2+   相似文献   

17.
The sorption of Cu(II) and Pb(II) to kaolinite-fulvic acid colloids was investigated by potentiometric titrations. To assess the possible interactions between kaolinite and fulvic acid during metal sorption, experimental sorption isotherms were compared with predictions based on a linear additivity model (LAM). Suspensions of 5 g L−1 kaolinite and 0.03 g L−1 fulvic acid in 0.01 M NaNO3 were titrated with Cu and Pb solutions, respectively. The suspension pH was kept constant at pH 4, 6, or 8. The free ion activities of Cu2+ and Pb2+ were monitored in the titration vessel using ion selective electrodes. Total dissolved concentrations of metals (by ICP-MS) and fulvic acid (by UV-absorption) were determined in samples taken after each titration step. The amounts of metals sorbed to the solid phase, comprised of kaolinite plus surface-bound fulvic acid, were calculated by difference. Compared to pure kaolinite, addition of fulvic acid to the clay strongly increased metal sorption to the solid phase. This effect was more pronounced at pH 4 and 6 than at pH 8, because more fulvic acid was sorbed to the kaolinite surface under acidic conditions. Addition of Pb enhanced the sorption of fulvic acid onto kaolinite at pH 6 and 8, but not at pH 4. Addition of Cu had no effect on the sorption of fulvic acid onto kaolinite. In the LAM, metal sorption to the kaolinite surface was predicted by a two-site, 1-pK basic Stern model and metal sorption to the fulvic acid was calculated with the NICA-Donnan model, respectively. The LAM provided good predictions of Cu sorption to the kaolinite-fulvic acid colloids over the entire range in pH and free Cu2+ ion activity (10−12 to 10−5). The sorption of Pb was slightly underestimated by the LAM under most conditions. A fractionation of the fulvic acid during sorption to kaolinite was observed, but this could not explain the observed deviations of the LAM predictions from the experimental Pb sorption isotherms.  相似文献   

18.
Humic Ion-Binding Model V, which focuses on metal complexation with humic and fulvic acids, was modified to assess the role of dissolved natural organic matter in the speciation of rare earth elements (REEs) in natural terrestrial waters. Intrinsic equilibrium constants for cation-proton exchange with humic substances (i.e., pKMHA for type A sites, consisting mainly of carboxylic acids), required by the model for each REE, were initially estimated using linear free-energy relationships between the first hydrolysis constants and stability constants for REE metal complexation with lactic and acetic acid. pKMHA values were further refined by comparison of calculated Model V “fits” to published data sets describing complexation of Eu, Tb, and Dy with humic substances. A subroutine that allows for the simultaneous evaluation of REE complexation with inorganic ligands (e.g., Cl−, F−, OH−, SO42−, CO32−, PO43−), incorporating recently determined stability constants for REE complexes with these ligands, was also linked to Model V. Humic Ion-Binding Model V’s ability to predict REE speciation with natural organic matter in natural waters was evaluated by comparing model results to “speciation” data determined previously with ultrafiltration techniques (i.e., organic acid-rich waters of the Nsimi-Zoetele catchment, Cameroon; dilute, circumneutral-pH waters of the Tamagawa River, Japan, and the Kalix River, northern Sweden). The model predictions compare well with the ultrafiltration studies, especially for the heavy REEs in circumneutral-pH river waters. Subsequent application of the model to world average river water predicts that organic matter complexes are the dominant form of dissolved REEs in bulk river waters draining the continents. Holding major solute, minor solute, and REE concentrations of world average river water constant while varying pH, the model suggests that organic matter complexes would dominate La, Eu, and Lu speciation within the pH ranges of 5.4 to 7.9, 4.8 to 7.3, and 4.9 to 6.9, respectively. For acidic waters, the model predicts that the free metal ion (Ln3+) and sulfate complexes (LnSO4+) dominate, whereas in alkaline waters, carbonate complexes (LnCO3+ + Ln[CO3]2−) are predicted to out-compete humic substances for dissolved REEs. Application of the modified Model V to a “model” groundwater suggests that natural organic matter complexes of REEs are insignificant. However, groundwaters with higher dissolved organic carbon concentrations than the “model” groundwater (i.e., >0.7 mg/L) would exhibit greater fractions of each REE complexed with organic matter. Sensitively analysis indicates that increasing ionic strength can weaken humate-REE interactions, and increasing the concentration of competitive cations such as Fe(III) and Al can lead to a decrease in the amount of REEs bound to dissolved organic matter.  相似文献   

19.
Electron spin resonance and infrared spectroscopic studies of lignite and ball clay from South Devon, and of extracts obtained from them by solvent fractionation, revealed similarities between corresponding organic components associated with both materials. All fractions exhibited a free radical resonance at g = 2.0037, which occurred with greatest intensity in the humic acids. Additional ESR features due to Fe3+, Mn2+ and VO2+ complexes were observed. Ferric ions give rise to resonances at g = 4.2 which have not been previously reported in the case of natural carbonaceous materials. It is shown that the paramagnetic species associated with the ball clay and lignite extracts do not significantly contribute to the observed ESR spectra of kaolinites, the latter being attributable to substituted Fe3+ ions and defect centres within the kaolinite lattice.  相似文献   

20.
Natural specimens of green gemological euclase (chemical formula BeAlSiO4(OH)) from Brazil were investigated by electron paramagnetic resonance (EPR) and optical absorption. In addition to iron-related EPR spectra, analyzed recently in blue and colorless euclase, chromium and vanadium-related EPR spectra were also detected in green euclase. Their role as color causing centers is discussed. The results indicate that Cr3+ ions substitute for Al3+ ions in the euclase structure. The EPR rotation patterns of Cr3+ with electron spin S = 3/2 were analyzed with monoclinic spin Hamiltonian leading to the parameters of g xx , g yy and g zz equal to 2.018, 2.001 and 1.956 and electronic fine structure parameters of D = −8.27 GHz and E = 1.11 GHz, respectively, with high asymmetry ratio E/D = 0.13. For the vanadium-related EPR spectra the situation is different. It is concluded that vanadium is incorporated as the vanadyl radical VO2+ with electron spin S = 1/2 with nearly axial spin Hamiltonian parameters gzz = 1.9447, g xx  = 1.9740 g yy  = 1.9669 and axial hyperfine interactions due to the nuclear spin I = 7/2 of the 51V isotope leading to A zz  = 502 MHz, A xx  = 150 MHz and A yy  = 163 MHz. The green color of euclase is caused by two strong broad absorption bands centered at 17,185 and 24,345 cm−1 which are attributed to the 4A2g → 4T2g, 4T1g transitions of Cr3+, respectively. Vanadyl radicals may introduce some absorption bands centered in the near infrared with tail extending into the visible spectral range.  相似文献   

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