|HERMOSIN, M. CARMEN|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2005
Publication Date: 1/6/2006
Citation: Cruz-Guzman, M., Celis, R., Hermosin, M., Koskinen, W.C., Nater, E.A., Cornejo, J. 2006. Heavy metal adsorption by montmorillonites modified with natural organic cations. Soil Science Society of America Journal. 70:215-221.
Interpretive Summary: If heavy metals accidentally reach high concentrations in soil as in an accidental spill, they have to be immobilized as soon as possible to avoid further potential water contamination.. The potential off-site movement of these metals can be decreased by creation of sorptive or immobilizing zones in the soils by incorporating an appropriate adsorbent in the affected area. Clays modified with organic cations have been shown to have potential to be adsorbents for some metals in these situastions. However, the nature of the organic cation on the clay influences the adsorption capacity and selectivity of organobentonites for selected metals. Consequently, a suitable selection of the chemical characteristics of a natural organic cation, as compared to the use of synthesized alkylammonium cations, can optimize the adsorbent properties for metals of the organoclays, which lack in general of specificity. In general, organoclays with high affinity for selected metals showed a higher resistance to desorption than organoclays with less affinity for them. These results reveal that organoclays might be potentially useful as agents to selectively immobilize metals in soils or to delay their movement towards underground waters and as supports these results will aid scientists in their development of inexpensive and efficient organoclays to be used to decontaminate spill sites. The viability of the use of natural organic cations to prepare organoclays is particularly interesting for minimizing the impact of the adsorbent once added to soil or aquifers.
Technical Abstract: Replacement of natural inorganic cations of clay minerals with organic cations has been proposed as a strategy to improve the adsorptive capacity of clay minerals for heavy metals. The organic cations most commonly used for this purpose have been quaternary ammonium ions containing alkyl or aryl chains without specific functional groups. In this work, we evaluated the ability of two bentonites (SWy-2 and SAz-1) exchanged with four natural organic cations containing diverse functional groups (L-carnitine, L-cysteine ethyl ester, L-cystine dimethyl ester, and thiamine) as adsorbents in a variety of heavy metals). For comparison purposes, the adsorptive properties of two “classical” organobentonites, hexadecyltrimethylammonium- and phenyltrimethylammonium-exchanged bentonites, were also determined. Most organobentonites displayed higher affinity for the metals than the untreated bentonite, but the improvement in adsorption capacity varied depending on the characteristics of the metal and the interlayer organic cation. The results demonstrate that selective modification of smectitic clay minerals with natural organic cations containing appropriate functional groups can be a useful strategy to improve their performance for the removal of specific heavy metals from the environment.