Metals humic substance interactions

Siripinyanond, A., Worapanyanond, S., and Shiowatana, J. (2005). Field-flow fractionation-inductively coupled plasma mass spectrometry An alternative approach to investigate metal-humic substances interaction. Environ. Sci. Technol. 39(9), 3295-3301. 

Interaction 3 shows metal-humic substances interacting through water bridging. It is a weak interaction involving metals with high hydration energy (Bohn et al., 1985). 

Figure 3.19 Schematic presentation of metal-humic substances complexation (adapted and modified from Stevenson, 1982, with permission). 1, Electrostatic interaction 2, inner-sphere complexation 3, weak water bridging.

Tipping, E. (1998). Humic ion-binding model VI an improved description of the interactions of protons and metal ions with humic substances, Aquat. Geochem., 4, 3-48. 

Raspor, B., Nurnberg, H.W., Valenta, P. and Branica, M., 1984. Studies in seawater and lakewater on interactions of trace metals with humic substances isolated from marine and estuarine sediments. 11. Voltammetric investigations on trace metal complex formation in the dissolved phase. Mar. Chem., 15 231-249. 

REACTIVITY OF HUMIC SUBSTANCES IN AMENDED SOILS 4.5.1. Interaction with Metal Ions... 

In the course of time it has been unambiguously demonstrated that humic- and fulvic acids interact with metal cations by forming rather stable, and often soluble complexes(1 2). The increasing awareness of a possible pollution of the environment, e.g. in connection with the disposal of nuclear waste, emphasizes the need for additional knowledge about the interaction between relevant metal ions, e.g. radionuclides commonly present in nuclear waste, and humic substances. The possible presence of soluble and rather stable complexes may play an important role in determining the migration behavior of the metal ions under shallow land burial conditions. The influence of humic- and fulvic acids on the migration behavior of metal ions has been discussed previously (2-6),... 

Allison, J.D. and Perdue, E.M. (1994) Modeling metal-humic interactions with MINTEQA, in N. Senesi and T.M. Miano (eds.), Humic Substances in the Global Environment and Implications on Human Health. Elsevier Science, Amsterdam, pp. 927-942. 

Typical values of pK[nt and pfor a humic acid are 2.67 and 4.46. The introduction of the electrostatic factor into the equilibrium constant is analogous to the coulombic term used in the definition of the intrinsic surface complexation constants. In addition another binding site (WAH) is recognised which is thought to behave as a weak acidic phenolic functional group. Although this site does not contribute to the titratable acidity and, therefore, no pK is needed for proton dissociation, it is involved in metal complexation reactions. The total number of the three monoprotic sites is estimated from titratable acidity and then paired to represent the humic substance as a discrete non-interacting mixture of three dipro-tic acids, which act as the metal complexation sites. The three sites are... 

Humic substance has a complex structure, comprising a hydrophobic core carrying functional radicals, mainly carboxyls and hydroxyls. Thus, humic substances can react with different products of various chemical functions, and so they interact ecologically with all classes of toxic products such as heavy metals, pesticides, etc. 

Commonly, the amount of metal ions adsorbed by the solid surface increases with increasing pH for humic substances, clays, or clay—humic acid mixtures. Metal-ions adsorbed in acid media increase with pH until the threshold value required for partial dissolution of solid and formation of soluble metal-humate complexes is exceeded (Fig. 3.18). Metal-organic complexes experience three types of interactions, which... 

Interaction 1 denotes electrostatic forces between humic substances (negatively charged) and metal ions (positively charged). It is a relatively weak interaction (outer-sphere complex) and the cation can be readily exchanged by other weakly bonding cations,... 

Metals constitute an important source of pollution in soils. As discussed in Chapters 5 and 6, they can bind to soils through humic substances, surface complex-ation, or ion exchange. In some cases more than one type of interaction can occur, as in clay minerals (e.g., montmorillonite and vermiculite) that bind metals through ion exchange as well as surface com-... 

Nissenbaum, A., and Swaine, D. Organic matter-metal interactions in Recent sediments The role of humic substances, Geochim. Cosmochim. Acta 40, 809-816... 

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