Specific adsorption of NOM

Adsorption of NOM onto mineral surfaces produces a composite that possesses physical and chemical properties distinct from either of its constituent components. The ill-defined, heterogeneous nature of NOM makes the interpretation of data from the characterization of naturally occurring OMN complexes problematic. In this respect, studies involving NOM- component classes (e.g., lipids, proteins, etc.) and reference minerals may offer insights. The characterization of model NOM-mineral composites provides the opportunity to employ techniques specific to the interaction of interest. 

Three specific areas can be identified to serve as foci for expanding the research on this material (i) The nature of the organic components interactions need to be ascertained. Do the lipids (whose chemistry is dominated by aliphatic components) and humic (whose chemistry is dominated by aromatic, carboxyl, and carbohydrate components) actually exist as distinct domains in organo-mineral complexes (ii) What is the effect of the mineral surface on adsorbed macromolecule conformation How does conformation impact the adsorption of additional NOM components (iii) Finally, a better understanding of the interfacial chemistry of these organo-mineral composites needs to be developed in order to understand the fate of many organic contaminants introduced into natural systems. 

In a recent review of technological alternatives for NOM removal, Jacangelo et al. [558] presented field data that illustrate wide variability in adsorption capacities of activated carbon in a single location (e.g., exhaustion periods between 41 and 182 days). They concluded that these results are evidence of the site-specific nature of [dissolved organic carbon] removal by [activated carbon] and that the concerns regarding reliability of treatment practices to meet the new [regulations] have a sound basis. Clearly, much fundamental work remains to be done to understand fully the complex nature of these adsorbent/adsorbate interactions and thus be able to optimize both the physical and the chemical accessibility of the carbon surface to natural organic matter. 

A number of studies have focussed specifically on the effect of NOM on the adsorption of TCE, particularly those by Kilduff and coworkers [31,53—56]. In summary, they concluded that the greatest effect on adsorption of TCE was achieved by preloading the activated carbon with low-molecular-weight NOM. They suggested the NOM occupied the high-energy adsorption sites, thus... 

Adsorption is the physico-chemical interaction between solutes and the membrane. The adsorption of organics, or more specifically humic substances, is considered a major fouling mechanism in water treatment. NOM can either adsorb in the structure of the cake and give the cake cohesion, or in the bulk of the membrane. These interactions are strongly influenced by membrane solute affinities and the... 

Figure 11. (A) Changes of specific adsorption capacity of SBIX to NOM during the experiment and (B) Linear form of exponential curve ADC vs. C for calculation of p and 6...

The retardation of subsurface transport of TNT arises from this compound s absorption into NOM and adsorption onto mineral siloxane surfaces covered with weakly hydrated cations like potassium (but not sodium and calcium). While components of feldspars exhibit some siloxane surfaces, here we anticipate that most of the silox-anes occur in the aluminosilicate clay minerals (e.g., illite) because these particles have such high specific surface areas (Table 11.3). Hence, the total for TNT may be found at this site ... 

Packed beds of activated alumina can be used to remove arsenic, fluoride, selenium, silica, and natural organic material (NOM) anions from water. The mechanism, which is one of exchange of contaminant anions for surface hydroxides on the alumina, is generally called adsorption, although ligand exchange is a more appropriate term for the highly specific surface reactions involved (2). 

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