Humic acids, interaction with clays

Since lignins are polymers of phenolics and are major plant constituents with resistance to microbial decomposition, they are the primary source of phenolic units for humic acid synthesis (178, 179). Once transformed, these humic acids become further resistant to microbial attack and can become bound to soils (180) form interactions with other high molecular weight phenolic compounds (ex. lignins, fulvic acids) and with clays (181) and influence the biodegradation of other organic substrates in soils (182, 183). 

Vecchio A, Finoli C, Simine DD, Andreoni V (1998) Heavy metal biosorption by bacterial cells. Fresenius J Anal Chem 361 338-342 Walker SG, Flemming CA, Ferris FG, Beveridge TJ, Bailey GW (1989) Physicochemical interaction of Escherichia coli cell envelopes and Bacillus subtilis cell walls with two clays and ability of the composite to immobililze heavy metals from solution. Appl Environ Microbiol 55 2976-2984 Wightman PG, Fein JB (2001) Ternary interactions in a humic acid-Cd-bacteria system. ChemGeol 180 55-65... 

Rashid, M. A., Buckley, D. E., and Robertson, K. R. (1972). Interactions of a marine humic acid with clay minerals and a natural sediment. Geoderma 8,11-27. 

Tombacz, E., Gilde, M., Abraham, I. and Szanto, F. (1988). Effect of electrolyte concentration on the interaction of humic acid and humate with montmorillonite, Appl. Clay Sci. 3, 31-52. 

Figure 5.3. A humic acid macromolecule interacting with a surface of a clay mineral. The proposed macromolecular structure of the soil humic acid (HA) is based on the following common average characteristics of humic acids MW 6386 Da elemental analysis (%) C, 53.9 N, 5.0 H, 5.8 0,35.1 S, 0.5 C/N, 10.7 NMR information (%) aliphatic C, 18.1 aromatic C, 20.9 carbohydrate C, 23.7 metoxy C, 4.9 carboxylic C, 8.4 ketone C, 4.5 phenolic C, 4.2 functional groups (cmol/g) carboxyl, 376 phenol, 188 total acidity, 564. The structure was created using the ACD/ChemSketch program. [HA-clay complex Chen s group, unpublished (2008). Individual HA molecule Grinhut et al., 2007.]...

Commonly, the amount of metal ions adsorbed by the solid surface increases with increasing pH for humic substances, clays, or clay—humic acid mixtures. Metal-ions adsorbed in acid media increase with pH until the threshold value required for partial dissolution of solid and formation of soluble metal-humate complexes is exceeded (Fig. 3.18). Metal-organic complexes experience three types of interactions, which... 

The zeta potential of bare kaolinite clay was determined to be —17.6 mV at pH 5.0. The strong interaction of aluminum ions with kaolinite clay at pH 5.0 was evidenced by (1) the positive values of the potential determined as a function of clay dose (Sample I) and (2) the low residual concentrations of aluminum ions in the supernatant as a function of the clay dose (Samples I and II) (Figure 25). Since the degree of hydrolysis of A1C13 determined at pH 5.0 is function of the aluminum ion concentration below a concentration of 10 mol/L, the net positive charge of the residual aluminum ions in the supernatant is expected to increase with clay dose. Therefore the interaction between modified clay and humic acids should be a function of the aluminum ion concentration, but in the present context only the relative concentration of aluminum ions and acidic groups a = [Al]/[RCOOH] is taken... 

In contrast to humic acids, proteins constitute a class of compounds that are chemically well defined, prevalent in soils, and able to form complexes with clay surfaces. Therefore, in order to study the interactions of anthropogenic chemicals with organic matter/clay complexes, we have started a series of MD simulations dealing with the adsorption of proteins by phyllosilicate surfaces. These investigations can be extended to humic acid coated clays, because many of the functional groups in proteins are the same as those in humic acids. 

Denecke MA, Reich T, Pompe S, Bubner M, Heise KH, Nitsche H, Allen PG Bucher JJ, Edelstein NM, Shuh DK, Czerwinski KR (1998b) EXAFS investigations of the interaction of humic acids and model compounds with uranyl cations in sohd complexes. Radiochim Acta 82 103-108 Dent AJ, Ramsay JDF, Swanton SW (1992) An EXAFS study of uranyl ions in solutions and sorbed onto sihca and montmorillonite clay colloids. J Colloid Interface Sci 150 45-60 d Espinose de la Caillerie J-B, Kermarec M, Clause (1995a) Impregnation of y-alumina with ( ) and ( ) ions at neutral pH Hydrotalcite-type coprecipitate formation and characterization J Am Chem Soc 117 11471-11481... 

A new research field in the chemistry of neptunium, plutonium, and other light actinides developed in the late 1970s in the context of environmental contaminations and nuclear waste management. The aim was to unravel their behavior in natural environments (see, e.g., Watters et al. 1983 Kim 1986). This is a difficult task because of the complex chemistry many oxidation states, polymerization, interaction with less defined natural partners such as humic acids, clays, and various rocks play a role. Included is also the development of techniques for the determination of actinide elements and their speciation in extremely low concentrations. 

Abstract The adsorption of ionic surfactants on different soil components such as silica, clay minerals, and humic acids was studied. The adsorption processes were controlled by flow microcalorimetry to determine the molar adsorption enthalpies of surfactant accumulation on clay and silicate surfaces. The evaluation of adsorption results for cationic surfactants has shown different mechanisms for solids having permanent (kaolinite, illite, montmorillonite) and pH-dependent surface charges (silica gels and powders). The adsorption mechanism for surfactants on silica surfaces with pH-dependent charges has been explained in terms of the development of charges on the surfaces and their interaction with... 

Considering the pH range 4—10 as the geochemical range, the redox potential due to the breakdown of water due to redox processes, the rare earths are predominantly present as Ln(III). Since the anions OH- and CO2 are present in natural environments, rare earths combine with these anions to form insoluble hydroxides and carbonates and hence immobilized. At lower pH, rare earth ions are adsorbed on clays, which are natural ion exchangers. The interactions of rare earth ions with humic and fulvic acids in soils, and Fe/Mn oxides are so strong, that they become immobile. 

A summary of the earlier studies with model compounds is in the classic review by M. M. Mortland, Qay-organic complexes and interactions, Advan. Agron. 22 75 (1970). See also D. J. Greenland, Interactions between humic and fulvic acids and clays, Soil Sci. 111 34 (1971). 

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