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Adsorption of humic substances on oxides

Organic adsorbates that are more hydrophobic exhibit different adsorption behavior, particularly at higher concentrations. Long-chain fatty acids adsorb to oxide surfaces in part through surface complexation, as shown by electron spin resonance spectroscopy (32). At higher concentrations at the surface, however, favorable interactions between sorbed molecules (hemimicelle formation) appear to dominate and result in greater than monolayer adsorption (40, 41). Because humic substances (like the fatty acids) are amphiphilic, both surface complexation and hydrophobic interactions may be involved in the adsorption of humic substances on oxide surfaces. [Pg.98]

The preceding discussion relies on an analogy between complexation in solution and complexation at the mineral surface, a fundamental tenet of the surface complexation model (27). Strong complexation of metals in solution by humic substances is well-documented (16, 42-44). Thus surface complex formation is a likely mechanism for the adsorption of humic substances on oxide surfaces. [Pg.102]

Adsorption of humic substances on oxides markedly affects particle surface charge and colloidal stability. In these effects, a contrast may be noted... [Pg.102]

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. [Pg.547]

Anion adsorption and then the exchange of anions mainly takes place on the protonated surface sites of silicates and other oxides (e.g., iron, manganese oxides) and hydroxides, as well as on the positive functional group (e.g., protonated amino groups) of humic substances. It is directed by electrostatic forces. The degree of anion exchange of rocks and soils is usually much less than that of cation exchange. [Pg.42]

An actual contribution of humic substances to metal oxide reduction in natural systems has not been demonstrated, and there are processes such as adsorption or decomposition that could limit their effectiveness. Kostka et al. (2002a) observed that AQDS additions elicited a larger increase in Fe(III) reduction by S. oneidensis growing on ferrihydrite than smectite clay minerals. This suggests that the influence of humic substances may depend on soil or sediment mineralogy. Nevertheless, there is ample evidence to suggest that a portion of the anaerobic metabolism that was previously attributed to direct enzymatic Fe(III) and Mn(IV) reduction was actually none-nzymatic reduction by microbially reduced humic substances. [Pg.4230]

Schlautman, M.A. and Morgan, J.J., Adsorption of aquatic humic substances on colloidal-size aluminum oxide particles Influence of solution chemistry, Geochim. Cosmochim. Acta, 58, 4293, 1994. [Pg.949]

The ability to control NOM adsorption through modification of surface chemistry was demonstrated previously [20] the uptake of several model humic substances and natural organic matter isolated from surface waters decreased significantly with increasing surface acidity (as measured by NaOH neutralization). The uptake was partially restored by subsequent heat treatment of the oxidized surfaces (i.e. OX 9/70 HT650). For the wood-based carbons, the impact of surface treatment on adsorption of organic matter was surprisingly small or absent. Overall, the reactivity of carbon surfaces to DOM uptake depended on the raw material type, activation conditions and surface treatment. [Pg.557]


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See also in sourсe #XX -- [ Pg.102 ]

See also in sourсe #XX -- [ Pg.102 ]




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Adsorption of humic substances

Adsorption on oxides

Adsorption/oxidation

Humic substances

Humic substances adsorption

Oxides adsorption

Substances oxidation

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