Humic 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. 

Cooke, J. D., Hamilton-Taylor, J., and Tipping, E. (2007). On the acid-base properties of humic acid in soil. Environ. Sci. Technol. 41, 465 70. 

To properly describe the acid-base properties of humic substances, it is essential that (1) the identification and quantification of acidic functional groups be accomplished in a rigorous, reproducible manner and (2) the range of pKa values that exists in humic substances be described by a suitable model that is as rigorous as possible. Despite years of research, neither of these objectives has been satisfactorily met. Consequently, it is not generally possible to compare results obtained by different scientists if different methods and/or humic samples have been used. 

Nbt only do the elemental composition, Mn, and aromaticity of a humic substance constrain the concentrations of acidic functional groups but they also give a crude picture of the spatial distribution of dipolar groups and formal charges in the vicinity of an acidic functional group. Such information is especially useful in evaluating the structural soundness of the multitude of models that are used to describe the acid-base properties of humic substances. 

Gustafsson, J.P, Modehng the acid-base properties and metal complexation of humic substances with the Stockholm humic model, J. Colloid Interf. Sci., 244,102, 2001. 

Summary of the acid—base properties of marine, fresh-water and soil humic compounds... 

The potentiometric titration curves of HA are usually broad and ill-defined, reflecting the varying properties of acidic groups on HA [23,24]. Wilson and Kinney [25] investigated the acid-base properties of lake water and marine humic substances and determined a two-step dissociation process. Schnitzer and... 

Plaza, C., N. Senesi, A. Polo, and G. Brunetti. 2005b. Acid-base properties of humic and ful-vic acids formed dnring composting. Environmental Science Technology 39, no. 18 7141-7146. 

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. 

Techniques used to separate humic substances from either a dissolved or sedimentary matrix rely on their acid-base solubility properties. In some of the separation techniques, it is likely that some nonhumic material accompanies the humic substances during the purification processes—to an extent... 

In a thorough paper that discusses many of the important properties of multiligand mixtures in the context of acid-base equilibria. Gamble (1970) has provided a direct method for estimating the distribution of pKa values in humic substances. Gamble assumes that a continuous distribution of nonidentical binding sites exists in humic substances and that the stoichiometric... 

Ertel, J. R. and Hedges, J. I. (1983). Bulk chemical and spectroscopic properties of marine and terrestrial humic acids, melanoidins, and catechol-based synthetic polymers. In Aquatic and Terrestrial Humic Materials (R. F. Christman and E. T. Gjessing, eds.). Ann Arbor Science, Ann Arbor, MI, pp. 143-162. 

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... 

Ertel, J. R. and J. I. Hedges. 1983. Bulk chemical and spectroscopic properties of marine and terrestrial humic acids, melanoidins and catechol-based synthetic... 

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