Fulvic acids acid-base properties

Plaza, C., Senesi, N., Polo, A., and Brunetti, G. (2005b). Acid-base properties of humic and fulvic acids formed during composting by the NICA-Donnan model. Environ. Sci. Technol. 39, 7141-7146. 

Ephraim, J. H., H. Boren, C. Petterson, I. Arsenie, and B. Allard. 1989. A novel description of acid-base properties of an aquatic fulvic acid. Environ. Sci. Technol. 23 356. 

Paxeus N. and Wedborg M. (1985) Acid—base properties of aquatic fulvic acid. Anal. Chim. Acta 169, 87 -98. 

Varney, M. S., Mantoura, R. F. C., Whitfield, M., Turner D. R., and Riley, J. P. (1983). Potentiometric and conformational studies of the acid-base properties of fulvic acid from natural waters. In Trace Metals in Sea Water Proceedings of the NATO Conference, 1981, pp. 751-772. 

Bowles E. C., Antweiler R. C., and MacCarthy P. (1989) Acid-base titrations and hydrolysis of fulvic acid from the Suwannee River. In Humic Substances in the Suwannee River, GA Interaction, Properties, and Proposed Structures, USGS Open File Report 87-557 (eds. R. C. Averett, J. A. Leenheer, D. M. McKnight, and K. A. Thorn), United States Government Printing Office, Washington, DC, pp. 209-229. 

Humic substances, humic and fulvic acids, are essentially a mixture of compounds of different molecular weights. The total number of base-titratable groups is in the range of 10-20 meq per gram of carbon. Chelation by neighboring carboxyl and phenolic groups is the major mode of metal complexation. Compounds such as malonic acid, phthalic acid, salicylic acid, and catechol serve as convenient monomeric model compounds for estimating the coordi-native properties of humic substances. 

Fractionation based on adsorption properties has been used particularly with fulvic acid fractions. Due to the nature of the extraction procedures used this... 

Humic substances have been arbitrarily divided into three diverse groups of compounds on the basis of their solubility in dilute acid and dilute base, Fulvic acids are soluble in both dilute acid (pH 1) and dilute base. Humic acids are soluble in dilute base but are precipitated by dilute acid (pH 1). Humin is insoluble in both dilute acid and dilute base. Some authorities divide humic substances into only two groups the humic acids and the fulvic acids, stating that the humins have the same characteristics as humic acids but that their solubility in base is hindered because they are associated with clay minerals in natural waters.The gross chemical and physical properties of humic acids and fulvic acids are presented in Table 5-12. It is the fulvic acid fraction that appears to... 

Structural representations of humic and fulvic acids are purely hypothetical and should just be considered as an attempt to rationalize chemical behavior. Several structural models have been proposed based on data gathered from degradative and nondegradative models. The different proposed models should be considered as complementary since each emphasizes certain particular properties. Briefly, humic acids are macromolecular and complex, and composed of substituted aromatic and aliphatic hydrocarbon core materials. It is probable that some aliphatic and aromatic ring compounds are heterocyclic with N, O, or S as the heteroatom. Segments or some side-chain components in the structures are substantially hydrophobic. In general, however, the... 

Humic substances are contained extensively throughout the environment (e.g., soils, sediments, surface waters, oceans, groundwaters, and swamps). These substances originate from the decomposition of animal and plant tissue with the variety of their chemical and physical properties dependent on their origin and age. Designation of the substances into chemical classes is not possible due to their complexity, even though research efforts to characterize them have been conducted for more than 200 years [96]. As a result, classification is based on the solubilities of the substances. Humic acids are only soluble at pH values >2 and fulvic acids are soluble at all pH values. 

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