Humic acid complexes

Magni et al. [857] studied the optimisation of the extraction of metal-humic acid complexes from marine sediments. Polyarylamide gels have been... 

Vitamin B12 catalyzed also the dechlorination of tetrachloroethene (PCE) to tri-chloroethene (TCE) and 1,2-dichloroethene (DCE) in the presence of dithiothreitol or Ti(III) citrate [137-141], but zero-valent metals have also been used as bulk electron donors [142, 143]. With vitamin B12, carbon mass recoveries were 81-84% for PCE reduction and 89% for TCE reduction cis-l,2-DCE, ethene, and ethyne were the main products [138, 139]. Using Ni(II) humic acid complexes, TCE reduction was more rapid, leading to ethane and ethene as the primary products [144, 145]. Angst, Schwarzenbach and colleagues [140, 141] have shown that the corrinoid-catalyzed dechlorinations of the DCE isomers and vinyl chloride (VC) to ethene and ethyne were pH-dependent, and showed the reactivity order 1,1-DCE>VC> trans-DCE>cis-DCE. Similar results have been obtained by Lesage and colleagues [146]. Dror and Schlautmann [147, 148] have demonstrated the importance of specific core metals and their solubility for the reactivity of a porphyrin complex. 

If the iron is present as humic acid complexes,11 these can be coagulated with alum (Section 14.2). Instead of trying to precipitate the iron, it may be better to keep it in solution, in which case it can be complexed with a chelating agent such as NTA3- or EDTA4. As a last resort, Fe2+ or Fe3+ can be removed by cation exchange, but the absorption on the zeolite or resin is usually irreversible. 

Saada, A., Breeze, D., Crouzet, C. et al. (2003) Adsorption of arsenic (V) on kaolinite and on kaolinite-humic acid complexes role of humic acid nitrogen groups. Chemosphere, 51(8), 757-63. 

Takamatsu, T. and Yoshida, T., 1978. Determination of stability constants of metal-humic-acid complexes by potentiometric titration and ion selective electrodes. Soil Sci., 125 377-386. 

Figure 3.7. Phenanthrene sorption isotherms on (A) the whole Amherst peat soil humic acid, (B) montmorillonite and a montmorillonite-humic acid complex (5 1 ratio), and (C) kaolin-ite and kaolinite-humic acid complex (5 1 ratio). Insets in parts B and C are the respective isotherms presented on a linear scale. Reprinted from Wang, K., and Xing, B. (2005). Structural and sorption characteristics of adsorbed humic acid on clay minerals. J. Environ. Qual. 34, 342-349, with permission from the Soil Science Society of America.

Singer, A., and Huang, P. M. (1988). Thermal analysis of AlOH polymer/montmorillonite/ humic acid complexes. Thermochim. Acta 135, 307-312. 

Tan, K. H. (1977). Formation of metal-humic acid complexes by titration and their characterization by differential thermal analysis and infrared spectroscopy. Soil Biol. Biochem. 10,123-129. 

Pandey, A. K., Pandey, S. D., and Misra, V. (2000). Stability constants of metal-humic acid complexes and its role in environmental detoxification. Ecotoxicol. Environ. Saf. 47(2), 195-200. 

Miano, T. M., Piccolo, A., Celano, G., and Senesi, N. (1992). Infrared and fluorescence spectroscopy of glyphosate-humic acid complexes. Sci. Total Environ. 123, 83-92. 

Dialysis has been used to study the interaction between radionuclides and humic acid. The technique gives information on 1) the complexing capacity of the humic acid samples, i.e. the concentration of complexing sites, and 2) the radionuclide - humic acid complexes by a) its stoichiometry (i.e. metal ion/ligand ratio), and b) interaction constants. 

Recently, Weber and co-workers reported on the application of dialysis to the determination of the complexing capacity of fulvic acid for a series of metal cations (19, 20). In the present paper we report a further elaboration on the dialysis technique to allow simultaneous determination of complexing capacity for the humic acid sample, and interaction constants for the metal ion - humic acid complexes, as well as the stoichiometry of the latter. The technique furthermore opens up a possibility for an indirect determination of apparent ionization constants for the humic acids. 

It shall be remembered that part of the metal ions, which are not engaged by the humic acid complexation, may interact with the buffer solution, containing a certain concentration of 1 buffer -ligands1, [l], i.e. [M]f < [m]q. The metal ion - buffer-ligand interaction is given by the following set of equations ... 

A deeper insight in the actual nature of the radionuclide -humic acid complexes requires further investigations, which, however, are outside the scope of the present work. 

Rate, A.W., McLaren, R.G. and Swift, R.S. (1992) Evaluation of a log-normal distribution first-order kinetic model for copper(II)-humic acid complex dissociation. Environ. Sci. Technol, 26,2477-2483. 

To a large extent, xenobiotic compounds in the aquatic environment are bound with sediments and suspended solid materials, such as humic acids. This binding plays a large role in biodegradation. Indeed, the structure of the bound form of the xenobiotic, such as a humic acid complex with a synthetic organic compound, may largely determine its rate of enzymatic degradation. 

Soil. Strongly absorbed by soil/humic acid complex and is virtually immobile in soil. Rapidly degraded in soil, with a half-life of <7 days. The principal degradation products are 4-chlorophenylurea and 2,6-difluorobenzoic acid... 

Initiation of iron oxide dissolution, humic acid complexation of trace metals and trace metal co-precipitation with FeS... 

Maximum dissolution of Fe and Mn oxides increasing sulfide production Co-precipitation of metals with FeS, and humic acid complexation... 

Several studies have shown that actinide-humic acid complexes are thermodynamically stable in high-ionic-strength solutions (Czerwinski et al, 1996 Marquardt et al., 1996 Labonne-Wall et al, 1999). However, destabilization of humic colloids at high ionic strength (Buckau et al, 2000) and competition for humic... 

Indeed, the metal humic acid complexation constants obtained for trace metals correlate reasonably well with the hydroxide and carbonate stability constants of the metals (Turner et al., 1981). Humic and fulvic acid complexation is therefore most likely to be significant for those cations that are appre-... 

Humic acid complexation will generally be less significant in seawater than... 

From the extraction in NaOH solution we may consider the stability order of Me-humic acid complexes. The order is Cu Zn> Mn> Fe. Copper forms more stable complexes with humic acid than zinc, in accordance with data available in literature for, soils (9-12), as well as manganese which forms complexes... 

One potential problem to be considered in dealing with this type of matrix is that derived from the salt content and the potential presence of humic material. In fact, a high salt content considerably hinders freeze-drying also, humic acid complexes are structurally altered — and often rendered either insoluble or difficult to dissolve — upon freeze-drying, which makes reconstituting the sample especially difficult [68]. 

For metal-humic acids complexes solubilization, 5 g of finely powdered sediment dried at 45°C are shaken with 0.1 M acetic acid and the treatment is repeated until the carbonates are completely removed. After centrifugation and washing with water, 0.5 M NaOH (degassed with N2) is added and shaken for 24 hr in order to extract the complexes. The extraction is repeated with a fresh 0.5 M NaOH solution and the two extracts are combined. The resulting alkaline solution is filtered through a 0.45 pm Millipore filter and analyzed by ICP-AES. After purification of the extracted humic acids by precipitation and redissolution, they are extracted into chloroform by means of cetylpiridinium chloride and NaCl. The absorbance of the chloroform extract at 450 nm is then measured to determine the concentration of humic acids (51). 

NMR spectra of humin from three major types of depositional environments, aerobic soils, peats, and marine sediments, show significant variations that delineate structural compositions. In aerobic soils, the spectra of humin show the presence of polysaccharides and aromatic structures most likely derived from the lignin of vascular plants. However, another major component of humin is one that contains paraffinic carbons and is thought to be derived from algal or microbial sources. Hydrolysis of the humin effectively removes polysaccharides, but the paraffinic structures survive, indicating that they are not proteinaceous in nature. The spectra of humin differ dramatically from that of their respective humic acids, suggesting that humin is not a clay-humic acid complex. 

The major conclusions that can be drawn from these studies are that humin differs in many respects from associated humic acids, suggestive of the fact that humin is not a clay-humic acid complex, and that humin is composed of a significant fraction of paraffinic carbons derived most likely from algal or microbial sources. 

---