Humic matter and contaminants. General aspects and modeling metal ion binding

Abstract

Humic substances are soil and fresh-water components that play an important role in the binding and transport of both organic and inorganic contaminants. Transport of the contaminants due to ground-and fresh-water dynamics is directly related to the risks associated with contaminations. The mobility of soluble humic substances is related to their interaction with soil mineral particles. Some key references for the binding of organic and inorganic contaminants and for the binding of humics to mineral particles are presented. Humic substances also play a role in the analysis of the contaminants in natural waters and with remediation of water or soil polluted with pesticides, heavy metal ions, and radionuclides. These aspects are illustrated with some examples. The problems that are encountered with the modeling of the binding of contaminants to humics and of heavy metal ions in particular are illustrated by considering the nonideal competitive adsorption model (NICA) extended with electrostatic interactions. The NICA-Donnan model gives quite good results for the description of metal ion binding, as is illustrated for metal ion binding to purified peat humic acid (PPHA). Finally, some remarks are made with respect to the use of the NICA-Donnan model in general purpose speciation programs and of simplified versions of the model for predictions under restricted environmental conditions.

Predictive model of cationic surfactant binding to humic substances

“…The NICA equation for surfactant binding to the acid sites of a HS can be written as (8) where X S (mol/kg) is the bound amount of surfactant, When the binding is ideal, the affinity does not depend on the concentration or the binding and n = 1; eq. (9) reduces to the Langmuir equation.…”

“…Proton binding to HS is well studied; it can be used to characterize HS from physical point of view [1,2] and is the basis for a better understanding of the binding behavior of other ions [3]. Adsorption of heavy metal ions is well documented and both the NICA-Donnan model [4][5][6][7][8][9][10] and Model VI [11] are able to describe and predict metal ion binding to HS as a function of pH, salt concentration and concentration of other competing ions. Also complex formation of HS with cationic polyelectrolytes is well studied.…”

Interactions of calcium and fulvic acid at the goethite-water interface

“…1) (Koopal et al, 1994;Kinniburgh et al, 1996;Kinniburgh et al, 1999;Koopal et al, 2001). Three important aspects of the model are described below.…”

“…Ion binding to humic substances is a complicated process due to the chemical heterogeneity, electrostatic interaction, competition effects and variable stoichiometry of the binding. The NICADonnan model (NICA: Nonideal consistent Competitive Adsorption) (De Wit et al, 1993;Koopal et al, 1994Koopal et al, , 2001Benedetti et al, 1995;Kinniburgh et al, 1996Kinniburgh et al, , 1999Milne et al, 2001Milne et al, , 2003 and Model VI (Tipping, 1998) are two examples of the advanced models for the description of proton and metal ion binding to humics that can handle this complexity.…”

The Effect of Organic Matter Amendment on Native Soil Humic Substances

“…Of particular interest is the nonideal competitive adsorption (NICA) -Donnan model, which stands out from the others in terms of physicochemical realism, accuracy, number of applications, and possibility of incorporation in existing speciation programs (e.g., ECOSAT and Visual MINTEQ). This model addresses the binding site heterogeneity of HS by assuming a continuous distribution of proton binding sites, discriminates between chemical and electrostatic interactions, and takes into account ionic strength effects in a generic way by means of an electrostatic Donnan gel model (Koopal et al, 1994(Koopal et al, , 2001(Koopal et al, , 2005Benedetti et al, 1995Benedetti et al, , 1996aKinniburgh et al, 1996Kinniburgh et al, , 1999Milne et al, 2001 ). By fi tting the NICADonnan model to potentiometric titration data obtained at different ionic strengths, intrinsic (i.e., independent of pH, salt concentration, or metal concentration) acidbase properties of HAs and FAs can be probed.…”