Mechanisms of pore water organic matter adsorption to montmorillonite

• Published in: Marine chemistry 2000-08, Vol.71 (3), p.309-320
• Main Authors: Arnarson, Thorarinn S, Keil, Richard G
• Format: Article
• Language: English
• Subjects: Adsorption; Coastal sediments; Dissolved organic matter; Earth sciences; Earth, ocean, space; Exact sciences and technology; External geophysics; Geochemistry; Liberty Bay; Mechanisms; Mineralogy; montmorillonite; Physical and chemical properties of sea water; Physics of the oceans; Pore water; Puget Sound; Silicates; USA; USA, Washington, Puget Sound, Liberty Bay; Washington; Water geochemistry
• ISSN: 0304-4203; 1872-7581
• DOI: 10.1016/S0304-4203(00)00059-1

The extent and mechanisms of adsorption of marine pore water organic matter to montmorillonite were studied in a series of batch and sequential adsorption experiments. Pore water natural organic matter (pNOM) and easily extracted natural organic matter (eNOM) were collected from Liberty Bay (Puget Sound, WA, USA) sediments. The pNOM and eNOM were each divided into two size fractions using a 1000 D ultrafilter. Batch adsorption isotherms were approximately linear, and the >1000 D fractions of both pNOM and eNOM had larger partition coefficients ( K d) than the 1000 D pNOM and eNOM, and ∼1.6 l/kg for 1000 D fractions during batch isotherm experiments. Adsorption of NOM was found to decrease with increased temperature, suggesting that hydrophobic effects were not the dominant adsorption mechanisms in this system. Ion exchange was also not an important adsorption mechanism because adsorption increased with ionic strength. The observed enhancement in adsorption with ionic strength indicated that van der Waals interactions were important in the adsorption of NOM. Ligand exchange was found to be a significant mechanism since the presence of SO 4 2− in solution reduced the amount of NOM adsorbed. Ca 2+ enhanced adsorption slightly more than Na +, suggesting that cation bridging was involved. The relative contributions of van der Waals interactions, ligand exchange and cation bridging were estimated to be approximately 60%, 35% and 5%, respectively, for adsorption of NOM in a CaCl 2 solution.