Suspensions, humic particles

Figure 2.1. Percentage of adsorbed Cd or Zn ions extracted from humic acid suspensions by electrolyte solutions. W Humic acid I El Humic acid II. Symbols indicate mean SD. The lettered entries indicate systems in which the addition of clay particles (i = illite, m = montmorillonite) altered the recovery level. From [257]...

Majzik, A., and Tombacz, E. (2007b). Interaction between humic acid and montmorillonite in the presence of calcium ions II. Colloidal interactions Charge state, dispersing and/or aggregation of particles in suspension. Org. Geochem. 38,1330-1340. 

Another potential problem with the batch method of Zasoski and Burau (1978) is keeping the soil or colloid uniformly suspended. This could be difficult with sandy soils where the sand-sized particles could sink to the bottom of the reaction vessel, or with high organic matter soils. With the latter, humic materials could rise to the surface of the reaction vessel creating a nonuniform suspension. 

The hydrophobic character of organic pollutants means that they can be adsorbed by sediments or particles in suspension or bind to DOMs such as humic substances. The hydrophobicity of organic pollutants reduces the probability of finding them free in water. 

In Fig. 5-3 (bottom) we show the fi/2 for the sorption of metal ions by humic acid particles. In this case the amount of metal ions added to the suspension was always constant (0.02 mmolj.), but the initial metal content of the humic acid particles was selected as 0.2, 0.4, 0.6 and 0.8 inol kg dry... 

At the surface of the earth, there exist countless examples of suspensions, including the suspended mineral and humic matter particles carried by streams and rivers, and are found in lakes and oceans [4, 5]. The sediments formed from these suspensions, once the voids are filled in and cemented in place by other... 

Studies of humic materials employing fractal geometry have generally focused on solution-state samples, and most of these studies have been directed towards humic acid (Table 7.1). Exceptions to this generalization are studies using turbidimetry that characterize aqueous suspensions of humic acid particles [33-38] and the application of fractals to describe the surface morphology of humin [23-25]. 

There are other ways of defining the partition coefficient, e.g., not as amount in solution divided by total amount in suspension, but as concentration in water relative to concentration on suspended matter. Here, Kd is set to 0.1 as a default value, which means that 10% of X is in solution and 90% is particulate. In practice, it is evident that the Kd-value is not a constant, but a variable, which depends on, e.g., (1) the given substance X, (2) lake water pH (and all cluster parameters linked to pH, such as hardness, conductivity, alkalinity, etc.), which influences the equilibrium between X and the particulate phase and the aggregation processes of the carrier particles, (3) the presence of colored substances (humus), which often have a strong affinity to many types of suspended substances (like metals, organic toxins, radioisotopes, etc.), and (4) the character of the particulate phase (if this is clays, humic matter, Fe-oxides/hydroxides, etc.). So, in more extensive ecosystem models, one would need comprehensive submodels to predict the partition coefficient. 

In soils and clays the most generally present biopolymers that naturally occur in the adsorbed state on mineral and clay particles are humic substances , or humic acids these are decomposition products of lignin, whidi is the major non-cellulosic polymer in wood and other plant debris. Humic acids (also called allomelanins (Merck Index, 1989)) are for the greater part polyphenolic compounds, usueJly anionic polyelectrolytes, which can complex metal ions, and are surface active and thus capable, upon adsorption onto mineral particles, to enhance their suspension stability in aqueous media (Chheda and Grasso, 1994). 

---