Humic acids elemental composition

Humic acid Total acidity Elemental composition % ... 

Elemental Analysis. The elemental analyses are presented in Table IV. The atomic ratios H/C for all drinking water samples (nos. 1-10) were between 1.28 and 1.39. These values were comparable to humic acid derived from lake sediments. However, H/C ratios were much lower when compared to the chlorinated model humic substances (e.g., 1.04-1.08 for CFH-1 and CFH-2). Bromine was present in almost negligible quantities, whereas Cl varied between 0.3 and 2.4, and S varied between 0.9 and 2.7 in the drinking water organic matter. All fractions from drinking water showed similar elemental composition. However, they differed from the elemental composition of the CFH samples in all respects, especially in chlorine content. 

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. 

Humic acid is composed of aromatic, aliphatic and carbohydrate carbon compounds. An average humic acid s elemental composition is 55.1% C, 5.0% H, 3.5% N, 35.6% O, and 1.8% S (Rice and MacCarthy, 1991). Its molecular weight distribution is typically broad, and it is a relatively high-molecular-weight material relative to the fulvic acid isolated from the same soil or sediment. It s predominantly functionalized by carboxylic acid and phenolic groups. At least some components of humic acid are surface-active, and these components have been shown to form micelles in concentrated, alkaline aqueous solutions (Piret et al., 1960 Visser, 1964 Wershaw et al., 1969 Tschapek and Wasowski, 1976 Chen et al., 1978 Rochus and Sipos, 1978 Hayano et al., 1982 Hayase and Tsubota, 1984 Guetzloff and Rice, 1994). 

Soil- and sediment-derived fulvic acid is also composed of aromatic, aliphatic, and carbohydrate carbon components, though it is generally believed to be more aromatic than the humic acid from that same environment. A typical fulvic acid s elemental composition is 46.2% C, 4.9% H, 2.5% N, 45.6% O, and 1.2% S (Rice and MacCarthy, 1991). The carboxyl group is the predominant functional group in... 

Due to the complexities of the substances involved and the preliminary nature of the calculations discussed here, we do not make any definitive claims regarding fulvic or humic acid chemistry. The complexity and range of compositions found in fulvic and humic acids makes definitive conclusions based on a few simulations impossible. The value of this chapter hopefully lies in the hypotheses that we have suggested above and in the methodology developed for further simulations. The key elements of our methodology follow ... 

The product of interaction with the herbicides of 3 humic acids of synthetic, coal and peat origin, indicated as synthetic-2, coal-2 and peat-2 in Table 2, will specifically examined in the first part of this paper. The 3 original HA samples do not differ sensibly in their elemental and acidic functional group composition, but they show quite different ash content (Table 2). 

The above scheme provides further fractionation of humic acids allowing the separation of a fraction known as hymatomelanic acid and of fulvic acids in several fractions (B, D, etc.). Humin is commonly further purified of inorganic components. The elemental composition of the fractions obtained with this separation scheme from an uncultivated prairie brown soil (TypicXerochrept) is given in Table 14.1.1. 

Table I. Elemental composition and peak areas for quantitative NMR spectra of fulvic and humic acids.

Elemental composition, functional group analyses, spectral properties, and characterization of acid hydrolysates have shown that peat humic acids tend to be similar to those from mineral soils. NMR spectroscopy has revealed that peat fulvic acids are largely carbohydrate in nature while the residue of alkali extraction is not all humin. 

Elemental composition is one of the most essential characteristics of humic substances. Average elemental composition of humic substances was calculated and results are presented in Table 3. As shown, data for fulvic acid and humin are rare compared to those for humic acid. Interestingly, the average... 

The ratios of humic to fulvic acids in estuarine and coastal sediments range from 0.4 to 3.4, the higher values being associated with areas or sediments having a terrestrial influence (Palacas et al., 1968 Brown et al., 1972 Hue and Durand, 1973 Pelet and Debyser, 1977 MacFarlane, 1978). These values are also consistent with those from other marine and terrestrial environments (Ishiwatari, 1966 Kononova, 1975 Stuermer et al., 1978 Cronin and Morris, 1982). Other parameters measured on coastal humic substances, such as elemental composition, spectral properties, organic components, stable isotope ratios, or C ages (Pelet and Debyser, 1977 Stuermer et al., 1978 Benoit et al., 1979 Nissenbaum, 1979) are consistent with terrestrial or marine humic compounds, or a mixture of these two endmembers. 

FIGURE 9. Average elemental composition of humic acids and stable residues from marine and terrestrial organic matter, compared to average elemental composition of some biopolymers. 

Humin is commonly defined as the class of sedimentary humic matter that remains insoluble when sediments are treated with dilute alkali to extract the soluble humic and fulvic acids. Because of its insolubility and macromolecu-lar nature, humin has been the least studied of all humic fractions. The classification of humin as a separate class of humic substances was initially proposed at the turn of the century by Oden (1919), and this classification has been in use since then. Because of the many similar analytical characteristics (e.g., elemental compositions, functional group compositions, and infrared spectra) between humin and humic acids, and because of the known association of humin with inorganic clays, Khan (1945) and later Kononova (1966) regarded humin as being no more than a clay-humic acid complex. Consequently, Stevenson (1982) has recently questioned whether humin should be considered a separate class of humic substances. Treatment of humin with HF to destroy clays in many instances renders humin soluble in alkali (Stevenson, 1982). 

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