WHAM—a chemical equilibrium model and computer code for waters, sediments, and soils incorporating a discrete site/electrostatic model of ion-binding by humic substances

Ion binding to natural organic matter : competition, heterogeneity, stoichiometry and thermodynamic consistency

A unifying model of cation binding by humic substances

This paper describes several possible interactions among the different types of organic and inorganic aquatic colloids, based on our present knowledge of their size, electric charge, and conformation. The physicochemical properties of the different groups of colloids are described. Emphasis is placed on the various types of organic components, including fulvic compounds. Subsequently, the role of each colloid class is discussed with respect to homoaggregation (aggregation within a given colloid class) and heteroaggregation (aggregation among different colloid types). On the basis of a synthesis of literature reports, microscopic observations of natural colloids, experimental results obtained with model systems, and numerical simulations, it is concluded that the formation of aggregates in aquatic systems can be understood by mainly considering the roles of three types of colloids:  (i) compact inorganic colloids; (ii) large, rigid biopolymers; and (iii) either the soil-derived fulvic compounds or their eq...

A Generalized Description of Aquatic Colloidal Interactions: The Three-colloidal Component Approach

The pH-dependent adsorption of humic acid (HA) on magnetite and its effect on the surface charging and the aggregation of oxide particles were investigated. HA was extracted from brown coal. Synthetic magnetite was prepared by alkaline hydrolysis of iron(II) and iron(III) salts. The pH-dependent particle charge and aggregation, and coagulation kinetics at pH approximately 4 were measured by laser Doppler electrophoresis and dynamic light scattering. The charge of pure magnetite reverses from positive to negative at pH approximately 8, which may consider as isoelectric point (IEP). Near this pH, large aggregates form, while stable sols exist further from it. In the presence of increasing HA loading, the IEP shifts to lower pH, then at higher loading, magnetite becomes negatively charged even at low pHs, which indicate the neutralization and gradual recharging positive charges on surface. In acidic region, the trace HA amounts are adsorbed on magnetite surface as oppositely charged patches, systems become highly unstable due to heterocoagulation. Above the adsorption saturation, however, the nanoparticles are stabilized in a way of combined steric and electrostatic effects. The HA coated magnetite particles form stable colloidal dispersion, particle aggregation does not occur in a wide range of pH and salt tolerance is enhanced.

The effect of humic acid adsorption on pH-dependent surface charging and aggregation of magnetite nanoparticles

http://library.um.ac.id/free-contents/downloadpdf.php/buku/complexation-reactions-in-aquatic-systems-an-analytical-approach-j-buffle-translators-s-p-kounaves-a-kounaves-and-r-s-altman-12623.pdf

J. Buffle

Papers

Complexation reactions in aquatic systems : an analytical approach / J. Buffle, translators S.P. Kounaves, A. Kounaves and R.S. Altman