Ion Association with Humic Substances

CHARACTERISTICS OF HUMIC SUBSTANCES Humic substances are an extremely complex and diverse group of organic materials 

TABLE 5-11 Complexation of Metal Ions by Inorganic Ligands 

Metol Ion Petcent Comptexed with Indicated Ligand Peicent Com-plexed by HTA - after addition of 3 X 10- M OTA 

Source C. W. Childs, Pxoc. I4th Coal. Great La es fles., IS3-210 (1971). /ntJ, ssoc. Great Lakes Res. (Reprinted by permission of the International Association for Great Lakes Research.) 

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 

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