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Adsorption and desorption of aliphatic amines, amino acids and acetate by clay minerals and marine sediments

Author(s): Wang XC, Lee C

Abstract

The adsorption and desorption behavior of three aliphatic amines, three amino acids, and acetate by organic-free clay minerals (kaolinite and montmorillonite) and by marine sediment was studied in laboratory experiments using 14C-labeled compounds. These compounds were chosen to represent basic, neutral, and acidic functional groups. Adsorption partition coefficients ranged from < 0.5 to 4.2 for acetate, < 1 to 15 for monomethyl-, dimethyl- and trimethyl amine, and < 1 to 128 for alanine, glutamic acid and lysine. Single desorption experiments were conducted using these compounds to calculate desorption partition coefficients. Repetitive desorption experiments and a consecutive desorption model were used to calculate partition coefficients for the reversible and resistant components of desorption. Adsorption of the three positively-charged amines and lysine was mostly reversible, but glutamic acid, alanine and acetate exhibited irreversible association. This is most likely related to the different adsorption mechanisms caused by the different functional groups on these compounds. Ion exchange and electrostatic interactions are more important for the positively-charged compounds while chemical interactions with surface organic functional groups may be more important for the neutral and negatively-charged compounds. Adsorption of amines, amino acids and acetate is greater in sediments with a higher organic content although the acidic and neutral compounds were affected more than the basic compounds. Oxidation state of the sediments may also be an important factor in adsorption behavior.

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