Clay, colloidal adsorption

Weber, J.B. (1970b.) Mechanisms of adsorption of s-triazines by clay colloids and factors affecting plant availability. In F.A. Gunther and J.D. Gunther, eds., The Triazine Herbicides. Residue Rev., 32. New York Springer-Verlag, pp. 93-130. 

Although for the present purpose the negative adsorption had to be suppressed, for others it is important Donnan exclusion, pH establishment in soils, and salt-sieving. Traditionally, these topics have greatly benefited from studies with clay colloids. 

Arsenic is ubiquitous in nature and is found in detectable concentrations in all environmental matrices. The occurrence of As in the continental crust of Earth is usually given as 1.5 to 2.0 mg/1. The distribution of arsenic in nature is extremely variable, showing little correlation with geological formation, climate, or soil. Numerous minerals, rocks, sediments and soils contain arsenic partly as constituent of sulfide minerals or complex sulfides of metal cations and partly as a constituent retained by soils and/or sediments in occluded or adsorbed forms. The latter is manifested primarily by the adsorption or occlusion of As on hydrous A1 and Fe oxides, but these are not necessarily the only source. Arsenic is also adsorbed on clay colloid, is bound to organic matter and may form slightly water soluble compounds with Al, Fe, Ca and Mg in the soil matrix. Some of the more common minerals in soils are arsenopyrite (FeAsS), Orpiment (AsgSg) etc. 

Examples of the pH dependent adsorption of s-triazines by clay colloids and by organic soil colloids are shown in Figure 8. Both isotherms are L-shaped (71) showing that adsorbed species are in equilibrium with species in solution at each pH level. 

Durand G, Lafuma F, Audebert R. Adsorption of cationic polyelectrolytes at clay-colloid interface in dilute aqueous suspension—Effect of the ionic strength of the medium. Progr Colloid Polym. Sci 1988 76 278-282. 

Water and Waste Water Treatment. PAG products are used in water treatment for removal of suspended soHds (turbidity) and other contaminants such as natural organic matter from surface waters. Microorganisms and colloidal particles of silt and clay are stabilized by surface electrostatic charges preventing the particles from coalescing. Historically, alum (aluminum sulfate hydrate) was used to neutralize these charges by surface adsorption of Al cations formed upon hydrolysis of the alum. Since 1983 PAG has been sold as an alum replacement in the treatment of natural water for U.S. municipal and industrial use. 

The clay mineral bentonite (sodium montmorillonite) has an excellent ion exchange and adsorption capacity. Films can be applied to electrode surfaces from colloidal clay solutions by simple dip or spin coating that become electroactive after incorporation of electroactive cations or metal particles 136-143)... 

The surfaces of colloidal particles are often charged and these changes can arise from a number of sources. Chemically bound ionogenic species may be found on the surface of particles such as rubber or paint latex particles. Charged species may be physically adsorbed if ionic surface active materials, for example, have been added. A charged surface may occur on a crystal lattice. An example is the isomorphous substitution of lower valency cations such as aluminium for silicon in the lattice structure of clays. A further example is the adsorption of lattice ions... 

Feldspar, among many natural substances such as termite mount-clay, saw dust, kaolinite, and dolomite, offers significant removal ability for phosphate, sulfate, and color colloids. Optimization laboratory tests of parameters such as solution pH and flow rate, resulted in a maximum efficiency for removal of phosphate (42%), sulfate (52%), and color colloids (73%), x-ray diffraction, adsorption isotherms test, and recovery studies suggest that the removal process of anions occurs via ion exchange in conjunction with surface adsorption. Furthermore, reaction rate studies indicated that the removal of these pollutants by feldspar follows first-order kinetics. Percent removal efficiencies, even under optimized conditions, will be expected to be somewhat less for industrial effluents in actual operations due to the effects of interfering substances [58]. 

Kummert, R. Stumm,W. (1980) The surface complexation of organic acids on hydrous y-AI2O3. J. Colloid Interface Sd. 75 373—385 Rung, K.H. McBride, M.B. (1989) Adsorption of para-substituted benzoates on iron oxides. Soil Sd. Soc. Am. J. 53 1673-1678 Rung, K.H. McBride, M.B. (1989a) Coordination complexes of p-hydroxybenzoate on Ee-oxides. Clays Clay Min. 37 333-340 Kuntze, H. (1982) Iron clogging in soils and pipes. Analysis and treatment. DVWK Bull. 10. Parey, Hamburg, Berlin, 123 p. 

McBride, M.C. (1985) Influence of glycine on Cu adsorption by micro crystalline gibbsite and goethite. Clays Clay Min. 33 397-402 McCafferty, E. Zettlemoyer, A.C. (1970) Entropy of adsorption and the mobility of water vapor on a- Fe20. J. Colloid Interface Sci. 34 452-460... 

Mineral segregation in industry relies heavily on the selective adsorption of macromolecules onto the surfaces of those minerals that have particular industrial applications. This selectivity is governed mainly by the surface chemistry of the mineral and the type of polymer used as a flocculant. " Effectiveness of flocculation depends upon the charge, concentration and molecular weight of the polymer, and also the pH and salt concentration of the clay suspension. The bonding between the anionic flocculant polyacrylamide (PAM) and clay mineral surfaces has been effectively reviewed recently by Hocking et al and the reader is referred to this should they require an in-depth literature review. For more information on general colloidal chemistry of clay suspensions the reader is referred to the review of Luckham and Rossi." ... 

---