Humic acids formation

Identification, isolation, and removal of (polyhydroxy)benzenes from the environment have received increased attention throughout the 1980s and 1990s. The biochemical activity of the benzenepolyols is at least in part based on thek oxidation—reduction potential. Many biochemical studies of these compounds have been made, eg, of enzymic glycoside formation, enzymic hydroxylation and oxidation, biological interactions with biochemically important compounds such as the catecholamines, and humic acid formation. The range of biochemical function of these compounds and thek derivatives is not yet fully understood. 

In these circumstances—and in view of increasing industrial interest in coal-based humic acids as chemical source materials (4)—we thought it pertinent to reinvestigate the mechanism of humic acid formation and, as a first step, to direct particular attention to the development of acidity and alkali solubility during progressive uncatalyzed oxidation of a subbituminous coal (Table 1) with dry oxygen. The choice of this particular system is, prima facie, arbitrary since conversion of coal into humic acids can, in principle, be accomplished by several methods. (Among those commonly used are reactions... 

Thus put, details of the individual reactions—which are, in any event, certain to be complex—remain as undetermined and debatable as before. What becomes clear (and consistent with experiment) is that (a) product gases such as carbon dioxide can form via two fundamentally unrelated paths (b) humic acids can be abstracted by secondary degradation or by stripping reactions such as decarboxylation (i.e. by reactions respectively characterized by kn> fe, etc. and by k) (c) in a sequential reaction series such as Reaction 2, a zero rate of humic acid formation denotes establishment of a steady state condition rather than formation of a simple equilibrium of the type coal humic acids. 

Haider, K., and Martin, J. P. (1967). Synthesis and transformation of phenolic compounds by Epicoccum nigrum in relation to humic acid formation. Soil Sci. Soc. Am. Proc. 31, 766-772. 

Nissenbaum and Kaplan (1972), on the basis of their isotopic study, presented the idea that humic acid formation and transformation in marine sediments proceed by the following pathway (1) degraded cellular material (2) water-soluble complex containing amino acids and carbohydrates — (3) fulvic acids - (4) humic acid (5) kerogen. 

FIGURE 1. Representative structures in the dynamic continuum of fulvic and humic acid formation. For more details see Harvey et al. (1983). 

This theory of Swaby and Ladd assumes that native lignin may be the source of phenols and quinones that combine with amino acids or ammonia to form polymers but, until decomposed, lignin is not active in humic acid formation. Since humic acid shows poor crystallinity it is probably not synthesized enzymatically but by heterogeneous... 

MARTIN J.P. and HAIDER K. 1969. Phenolic polymers of Staohyhotvys astra Stachybotrys chartarum and Epicocoum nigrum in relation to humic acid formation. Soil Science, 107, 260-270,... 

MARTIN J.P., HAIDER K. and WOLF D. 1972. Synthesis of phenols and phenolic polymers by Mendersonula toruloidea in relation to humic acid formation. Soil Science Society of America Proceedings, 36, 311-315. 

Phosphorus (P) is one of the major limiting factors for plant growth in many soils. Plant availability of inorganic phosphorus (Pi) can be limited by formation of sparingly soluble Ca phosphates, particularly in alkaline and calcareous soils by adsorption to Fe- and Al-oxide surfaces in acid soils and by formation of Fe/ Al-P complexes with humic acids (94). Phosphorus deficiency can significantly alter the composition of root exudates in a way that is, at least in some plant species, related to an increased ability for mobilization of sparingly soluble P sources (29,31,71). 

In a recent study of the complexation of technetium with humic acid (HA) Sekine et al. [34,35] obtained interesting results which show competition between Tc,v-0(0H) i precipitate formation and Tcin-HA precipitate formation during a reduction process of pertechnetate with Sn2+. A weighable amount of... 

Organic matter is also the essential component of natural soils and its association with microorganisms may influence the behavior and fate of toxic metals. A variety of batch complexation experiments were performed by Borrok et al. (2007) in single, binary and ternary systems for the three components natural organic matter (NOM), bacterium (B. subtilis) and metals (Pb, Cu, Cd, and Ni) to determine the significance of ternary complexation. They found that the formation of bacteria-metal-NOM complex is a rapid, fully-reversible chemical process. The stability of bacteria-metal-NOM complexes increases with the decrease of pH. All NOM fractions form ternary complexes to similar extents at circumneutral pH, but humic acid becomes the dominant NOM fraction in ternary complexes at low pH. The abundance of humic acid in ternary form is greatest with Ni or Cd systems and less with Pb and Cu systems. Their results suggest that... 

Many of the methods used for lignins can also be applied to humic acids. Thus the use of pulse polarography after the formation of nitroso derivatives is possible with humic acids as well as lignins [433,443]. If the fulvic acids are... 

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