Humic coal substances

Coal is formed from peat and the vascular plant remains that accumulate in peat bogs. Anaerobic conditions are considered mandatory for the accumulation and preservation of peat and the formation of coal. Two major types of coals are known humic coal and sapropelic coal (see Breger, 1963, 1976). The former are formed from peat accumulations rich in humic substances derived predominantly from vascular plant remains. The latter represent coal formed from algal (boghead coal) or spore (cannel coal) accumulations. In many respects, sapropelic coal can be considered to have an aquatic origin similar to that of humin of aquatic sediments which forms from the accumulation of aquatic nonvascular plant debris in clastic sediments. Conversely, kerogen can also have the properties of humic coals (Breger and Brown, 1962) is the source materials to the sediment at the time of deposition are predominantly derived from vascular plants. 

The problems involved in the study of humic substances are, as expected, also encountered in the case of fossil fuels. Most C-13 CP/MAS spectra of solid fossil fuels (coals, oil shales) do not exhibit a high level of spectral resolution50,51). They consist essentially of two broad bands — one in the aromatic/olefinic region from about 170 ppm to 95 ppm and one in the aliphatic region from about 90 to —5 ppm relative to TMS. On the other hand, lignite, an imperfectly formed coal, shows a considerable amount of fine structure. 

Hatakka A (2001) In Hofrichter M, Steinbiichel A (eds) Biopolymers lignin, humic substances and coal, 1st edn. Wiley-VCH, Weinheim, p 129... 

Kulikova N, Perminova I (2002) Binding of atrazine to humic substances from soil, peat, and coal related to their structure. Environ Sci Technol 36 3720-3724... 

Commercially Available Humic Acids. A large quantity of the commercially available humic acids was purchased from Fluka AG (Buch, Switzerland) by the Health Effects Research Laboratory (HERL) of the U.S. Environmental Protection Agency (USEPA), Cincinnati, Ohio. This coal-based humic substance is from West Germany. 

Conversely, the coal-based Fluka humic acid may be too different from the aquatic humic matter in terms of molecular weight, solubility, and functional group to serve as the best model for toxicological evaluation of drinking water-derived substances. 

B. K. Mazumdar. Low rank coals like lignites and natural humic acid derived from such coals are known to contain alicyclic structures in their constitution. How does the author envisage the formation of such structures in the transformation of lignin to humic acid-like substances ... 

Jince the time of Berzelius, chemists have proposed structures for the amorphous, black substance known as humic acid. In the past 150 years, much experimental work has appeared on the nature of humic acid, most of it based on classical chemical and microbiological studies. Very little information about the molecular structure of humic add has resulted from these studies however. Some of the problems plaguing investigators in this field have been (a) variation in the source of humic acid, (b) variation in the definition of humic fractions of soil and coal, (c) lack of crystallinity of the samples, (d) uncertainty of molecular weight measurements, (e) variation in extraction techniques, and (f) variation in elemental composition. The little unambiguous information that exists today is based on extensive degradation of the humic acid polymer and represents only a small fraction of the total molecule. 

Vauquelin (14), A. Klaproth (6), and R. Jameson (5), alkali soluble organic constituents of soil and coal are designated as humic acids/ Collectively, these substances make up an ill-defined series of dark colored, weakly acidic solids which form whenever plant components (such as lignin) are exposed to fungal oxidases, or when coal is allowed to weather or otherwise oxidize. Some evidence now exists that humic acids isolated from these varied sources do indeed contain several common peripheral structures (2, II, 16), but by any more discriminating test, the term possesses little chemical significance or fixed meaning. 

Piccolo, A., Celano, G., and Pietramellara, G. (1993). Effects of fractions of coal-derived humic substances on seed-germination and growth of seedlings (Lactuga sativa and Lycopersicon esculentum). Biol. Fertil. Soils 16(1), 11-15. 

Various separation methods have been used to isolate, fractionate, and characterize humic materials. Originally it was fractionation, based on solubility differences of humic components in diluted alkalis and acids, which laid the ground work for the first classifications of humic substances (HS) in the 19th century (Mulder, 1861 Sprengel, 1837) and provided for operational definition of HS (Kononova, 1966). And now, alkali extraction is the method of choice for isolating HS from solid humus-containing substrates like soil, peat, coal, and so on (Swift, 1996), while hydrophobic resins (e.g., Amberlite XAD resins) are typically used to extract HS dissolved in natural waters (Aiken, 1985). Initial research on HS began with the used simple separation methods to prove, examine, and define characteristics of components of humic matter (Oden, 1919).Today, however, advances in HS research require ever more sophisticated techniques of separation combined with structural analysis (Orlov, 1990 Stevenson, 1994). 

Comparable infrared (IR) spectra of complex organic solids such as coals (Fig. 7) 23), cherts, kerogens, humic substances and some natural polymers have been presented in various publications. They show a limited number of rather broad bands which are due to well defined chemical groups and can often be interpreted by comparison to less complicated spectra. The signals commonly observed in fossil organic matter are as follows (Robin et al., 1977 21), Tissot Welte, 1978 24), Rouxhet et al., 1980 22>, Friedel Carlson, 1972 25)) ... 

Although originally developed for research purposes on soil and coal-derived HAs (Blom et al., 1957 Brooks and StemheU, 1957 Schnitzer and Gupta, 1965), indirect titration methods were also applied to aquatic samples in the 1970s. For example. Beck et al. (1974) analyzed 10 unfractionated DOM samples from a blackwater river in southeastern Georgia (USA), and Weber and Wilson (1975) analyzed three FAs from a darkly colored river and pond in New Hampshire (USA). It was later recognized (Sposito and Holtzclaw, 1979 Perdue et al., 1980) that incomplete removal of a humic substance from a Ca(CH3C02)2 reaction mixrnre causes carboxyl content to be overestimated. Davis (1982) found that incomplete removal of a humic substance from a Ba(OH)2 reaction mixture causes total acidity to be underestimated. The critical nature of the filtration step in indirect titrations was further discussed by Perdue (1985). 

The principal degradation mechanism of organic matter in the formation of peats (humic substances included) and leading to the formation of coal, therefore, appears to involve the preferential breakdown of labile biomolecules (carbohydrates, etc.), and the selective preservation of inert and relatively inert (i.e., somewhat degraded) biomolecules (Hatcher and Clifford, 1997). Melanoidin formation may also play some role in the... 

Although NMR is probably the most widely used NMR technique in chemical applications, it has only been used sparingly in studies of humic substances. Much of the literature in which this technique is used was published prior to 1987 and is well covered in the review by Wilson.(5) Use of NMR is mostly limited to solutions, and it is thus necessary to dissolve humic substances in aqueous solutions. Of course, one must reduce the amount of H s from solvent molecules by use of deuterated water, but it is often difficult to reduce these background signals to negligible amounts. Wilson(5) described the application of water suppression techniques which have been necessary to obtain H NMR spectra of humic isolates from soil. In the case of solid-state NMR of whole soils and humic substances, the development of a new technique called CRAMPS (combined rotation and multiple pulse spectroscopy) has not received the attention it has in the field of coal science, primarily because of the lack of resolution. Thus, recent applications of either solution or solids NMR has been very limited in humic substance science since Wilson s(5) review. 

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