Metal Ion Binding by Humic Acid:  Application of the NICA-Donnan Model

Abstract

A Donnan-type model for nonspecific binding of electrolyte ions has been combined with the non-ideal competitive adsorption (NICA) model for specific binding to produce a model for ion binding to humic substances. The model considers site heterogeneity, non-ideality, multicomponent competition, and electrostatic interactions. The NICA-Donnan model was fitted to data for H, Ca, Cd, Cu, and Pb binding by a purified peat humic acid. The model fits were good and covered a wide range of pH and free metal concentrations. The parameters from these single metal data sets were then used to predict the competitive effect of Ca on Cd and Cu binding at various pHs. These predictions agreed well with the experimental data although there were some small but systematic differences. The new NICA-Donnan model also predicted reasonably well the increase in Cd and Cu binding on changing from a 0.1 M KNO3 background electrolyte to 0.01 M KNO3. A shortcoming of the model is that in some cases it significantly underestimated the H+/M2+ exchange ratio, especially at high pH and for Cu binding.

Adsorption of metal ions on lignin

“…Lignin contains two major types of functional groups that have strong interactions with metal ions: carboxylic and phenolic groups [41][42][43]. These two types of sites have often been used to describe the metal ion binding to humic substances, which contain carboxylic and phenolic groups as the main surface functional groups [44][45][46]. Therefore a two-site model was used to fit the titration data.…”

Cu2+ and Ca2+adsorption to goethite in the presence of fulvic acids

“…Copper or calcium adsorption to FA in the binary system of Cu-FA or Ca-FA is described with the NICA-Donnan model (De Wit et al, 1993a,b;Benedetti et al, 1996;Kinniburgh et al, 1996;Kinniburgh et al, 1999;Tipping, 1998;Van Riemsdijk et al, 2006), whereas Cu or Ca adsorption to goethite in the binary system of Cu-goethite or Ca-goethite is described with the CD-MUSIC model (Hiemstra et al, 1989a;Hiemstra and Van Riemsdijk, 1996). Adsorption of Cu or Ca in the ternary systems (Cu-FA-goethite, Ca-FA-goethite) is described using the linear additivity approach as well as the LCD (Ligand and Charge Distribution) model (Filius et al, 2001(Filius et al, , 2003Weng et al, 2005Weng et al, , 2006Weng et al, , 2007.…”

Colloids and suspended particulate matters influence on Ni availability in surface waters of impacted ultramafic systems in Brazil

“…The 61 Ni/ 58 Ni isotopic ratio was measured in the filtrate, the spike and the standard solutions (2) where C SPM represents the mass concentration of SPM (kg L -1 ). This parameter not only allows comparing results between all four water samples, but it also permits to establish a direct comparison between Ni exchangeable pool and dissolved Ni in a given natural water sample, which provides an interesting environmental approach.…”

“…partly resulting from high temperature processes during ore calcination for NIQ 1 and 2), the DOC was considered as generic fulvic acids and modeled using the NICA-Donnan model [58]. Important differences between BA and NIQ samples can be observed regarding the system saturation with respect to Fe oxy-hydroxides.…”