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United States Department of Agriculture

Agricultural Research Service

Title: Mechanisms for Sorption of Organic Bases on Mineral Surfaces in Aqueous Systems

item Laird, David

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: October 31, 1997
Publication Date: N/A

Technical Abstract: Mechanisms by which organic bases are sorbed on hydrated smectite surfaces were investigated. Three Ca-saturated reference smectites (Otay, SPV, and Panther Creek) were dispersed in distilled water containing 5 micromoles of pyridine or 3-butylpyridine. The pH was adjusted between 7.5 and 3 using 0.01 M HCl. After a 2 h equilibration, the amount of pyridine or 3-butylpyridine sorbed on the clay and the amount of Ca desorbed from the clay were determined. The results indicate negligible sorption of pyridine for neutral systems and nearly total sorption of pyridine for pHs less than the pKa of pyridine (5.20). Equivalent amounts of Ca were desorbed from the clays indicating that pyridine was sorbed as a protonated species by ion exchange. By contrast, 40 to 90% of added 3-butylpyridine was sorbed on the clays at neutral pHs while only small amounts of Ca were desorbed. The results suggest that 3-butylpyridine is initially retained by hydrophobic bonding between the alkyl tail of the molecule and hydrophobic microsites located between the charge sites on smectite surfaces.

Last Modified: 4/21/2015
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