Submitted to: Clay Minerals Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/11/2009
Publication Date: 6/11/2009
Citation: Boyd, S.A., Johnston, C.T., Laird, D.A., Teppen, B.J., Li, H. 2009. A Comprehensive Analysis of Organic Contaminant Adsorption by Clays [abstract]. In: Programs and Abstracts, Clay Minerals Society 46th Annual Meeting, June 5-11, 2009, Billings, MT. p. 73. Interpretive Summary:
Technical Abstract: Macroscopic studies of nonionic organic contaminant (NOC) sorption by clays have revealed many important clues regarding factors that influence sorption affinity, and enabled the development of structural hypotheses for operative adsorption mechanisms. Integrating this understanding with knowledge gained from complementary molecular scale methodologies including X-ray diffraction, vibrational spectroscopies and molecular/quantum mechanical simulations has provided a comprehensive view of the central structural factors, forces and mechanisms responsible for NOC sorption by smectite clays. Based on these studies, we conclude: (1) Sorption of NOCs by smectites can take values along a continuum from zero up to 100 g NOC per kg clay. The critical factors that control sorption are a complex interplay among the functional groups of the NOC, the layer charge of the clay mineral, and the hydration of interlayer cations. (2) An optimal inorganic sorbent for NOCs should be a Cs+-saturated smectite with a low layer charge resulting from tetrahedral substitution. These criteria maximize the size and hydrophobicity of adsorption domains parallel to the clay surfaces while optimizing (near 12.5 Å) the adsorption domains perpendicular to the clay surfaces to promote solute dehydration and interaction with opposing siloxane sheets. Such clays may adsorb 10% of their weight for NOCs with multiple, strongly complexing functional groups (for such solutes, K-smectites are nearly as effective). In contrast, such clays adsorb only 1% by weight of more hydrophobic NOCs that lack the ability to form strong complexes with interlayer cations.