Humic substances adsorption

Gjessing (1976) found a markedly increased adsorption of aquatic humic substances onto montmorillonite with decreasing pH, which could be explained by charge neutralization of the humic substances. For soil humic substances, adsorption is assumed to be partly interlamellar, which requires... 

Newcombe G. (1994). Activated carbon and soluble humic substances adsorption, desorption, and surface charge effects. J. Colloid Interface Sci., 164, 452-62. 

Aggregation and fragmentation of colloidal particles has been investigated further employing natural polyelectrolytes like humic substances. Adsorption of humic acids on aluminum oxide was determined to resemble interfacial deposition on the basis of methods previously employed for the aluminum oxide/polyacrylic acid system [88]. Complexation by soluble aluminum ions produces pH drops that are very similar to that determined for polyacrylic acid, and essentially humic acids were determined to exert effects on the stability of colloidal aluminum oxide particles at pH 5 that are very similar to polyacrylic acid. 

Adhikari M, Das PK, Das K. 1986. Studies on adsorption and desorption of methyl parathion on humic substances. J Indian Chem Soc 63 1027-1029. 

Ochs, M. (1991), Humic Substances at Aquatic Interfaces A Comparison of Hydrophobic vs Coordina-tive Adsorption and Subsequent Effects on Mineral Weathering, Ph.D. Thesis, ETH Zurich, Switzerland. 

Keywords. Sorption, Interaction mechanisms, Organic pollutants, Solid phases, Adsorption, Partitioning, Humic substances, Humus, Organic matter... 

Adsorption mechanisms represent probably the most important interaction phenomena exerted by solid surfaces on the environmental fate of organic pollutants [65, 127-130]. Adsorption controls the quantity of free organic components in solution and thus determines their persistence, mobility, and bioavailability. The extent of adsorption depends on the amount and properties of both solid phase-humic substances (SPHS) and organic pollutants. Once adsorbed on an SPHs >an organic pollutant may be easily desorbed, desorbed with difficulty, or not at all. Thus sorption phenomena may vary from complete reversibility to total irreversibility. 

It is commonly reported that dissolved humic substances (i. e., DHS) tend to coat mineral particles and thereby affect the surface chemistry of those materials. DHS coat the surfaces of solid particles even when they are present at very low concentrations. They furthermore impart a negative charge to the surfaces which they coat. The organic coating is expected to have a great significance on subsequent adsorption of various pollutants [88,91-93,287,288]. 

Recall from Chapter 23.2.4 that humic substances are isolated from seawater by adsorption on a hydrophobic resin followed by elution using solvents of varying pH. The desorbed compounds are fractionated into two classes, humic acids fulvic acids based on their solubility behavior. A model structure for a humic acid is illustrated in Figure 23.10a in which fragments of biomolecules, such as sugars, oligosaccharides. 

Amy, G.L., Narbaitz, R.M., and Cooper, W.J. Removing VOCs from groundwater containing humic substances by means of coupled air stripping and adsorption, J. Am. Water Works Assoc., 79(l) 49-54, 1987. 

Piccolo, A., Celano, G., and Conte, P. Adsorption of gl3q)hosphate by humic substances, J. Agric. Food Chem., 44(8) 2442-... 

Humic substances. Analogous to the reactions described above, humic substances (the polymeric pigments from soil (humus) and marine sediments) can be formed by both enzymatic and non-enzymatic browning. High concentrations of free calcium and phosphate ions and supersaturation with respect to hydroxyapatite can sustain in soil, because adsorption of humic acids to mineral surfaces inhibits crystal growth (Inskeep and Silvertooth, 1988). A similar adsorption to tooth mineral in a caries lesion can be anticipated for polycarboxylic polymers from either the Maillard reaction or enzymatic browning. 

Zhang X, Minear RA (2006) Formation, adsorption and separation of high molecular weight disinfection byproducts resulting from chlorination of aquatic humic substances. Water Res 40(2) 221-230... 

Clay minerals, oxides, and humic substances are the major natural subsurface adsorbents of contaminants. Under natural conditions, when humic substances are present, humate-mineral complexes are formed with surface properties different from those of their constituents. Natural clays may serve also as a basic material for engineering novel organo-clay products with an increased adsorption capacity, which can be used for various reclamation purposes. 

Schofield RK, Samson HR (1954) Flocculation of kaolinite due to the attraction of opposite charged crystal faces. Discuss Faraday Soc 18 135-145 Schofield RK, Samson HR (1953) The defiocculation of kaolinite suspensions and the accompanying change-over from positive to negative chloride adsorption. Clay Miner BuU 2 45-51 Schulten HR (2001) Models of humic structures association of humic acids and organic matter in soils and water. In Qapp CE et al. Humic substances and chemical contaminants. Soil Science Society of America, Madison, Wl, pp 73-88... 

The toxin is also likely to be adsorbed or complexed by soil humic acids. If the reaction is a simple adsorption reaction, all or part of the toxin might later become available for absorption by a receiver plant. If the toxin is complexed or precipitated by its reaction with soil humic substances, then it would be deactivated. 

The behavior of phenolic compounds derived from decaying plant residues, or released from degrading humic substances, is dictated by the physico-chemical processes of adsorption and desorption. Equilibria between these processes determine the concentration of phenolic compounds in the soil solution and consequently the bioactivity, movement, and persistence of these substances in the soil. Surface interactions between phenolic compounds and colloidal matrices may promote their polymerization (25, 26) or protect them from microbial degradation and mineralization. 

---