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

Abstract

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 equivalent in pelagic waters, aquagenic refractory organic matter. In most natural aquatic systems, the small (few nanometers) fulvic compounds will stabilize the inorganic colloids whereas the rigid biopolymers (0.1−1 μm) will destabilize them. The concentration of stable colloids in a particular aquatic system will depend on the relative proportions of these three components.

The effect of humic acid on the aggregation of titanium dioxide nanoparticles under different pH and ionic strengths

“…Humic substances (HS) represent an active and important fraction of natural organic matter (NOM), and they play important roles in the fate and transport of pollutants (Aiken, 1985;Buffle et al, 1998;Zheng et al, 2008). HS can be categorized into three groups: fulvic acids (FAs), which are the major component and the smallest structures of HS, and are soluble at any pH; HA, which represents bigger structures that are insoluble at pH b 2; and humin, which is insoluble at any pH (Jones and Bryan, 1998;Piccolo, 2001).…”

Contrasting Roles Of Natural Organic Matter On Colloidal Stabilization And Flocculation In Freshwaters

“…Instead of decreasing the coagulation rates of the inorganic particles as has been observed for the HS (Tipping and Higgins 1982;Amal et al 1992)(see Chpater 5), it has been suggested that the rigid biopolymers may increase the coagulation rate of inorganic particles Buffle et al 1998).…”

“…Inorganic particles are generally electrically charged due to the isomorphic substitution of ions in the bulk solid phase, or to the reactions of surface functional groups with dissolved ions in the aqueous phase (Sposito 1993). Apart from the iron oxyhydroxydes which are neutral or positively charged in the circumneutral pH range, the major inorganic colloids are generally negatively charged in water due to their low zero point of charge (Table 1; (Lerman 1979;Buffle et al 1998)). It is therefore reasonable to represent the submicron inorganic colloids as compact, often negatively charged particles that cover the whole colloidal size range.…”

“…They originate from the transformation of plant and animal matter into relatively stable, polydisperse macromolecules that have molar masses ranging from hundreds to a few thousands of Daltons Buffle et al 1998). They are found in most soils, sediments, and natural waters.…”

Comparison of two cationic polymeric flocculant architectures on the destabilization of negatively charged latex suspensions

“…Trace metals and organic pollutants are mainly adsorbed at the surface of mineral particles like silicates, alumino-silicates or iron oxyhydroxides [3,4] owing to their high specific surface area, diffusivity and reactivity. In these systems algal and bacterial exudates composed of polysaccharide chains promote the flocculation of these mineral particles and the subsequent removal of pollutants.…”