Role of organic acidity in sorption of natural organic matter (NOM) to oxide surfaces

Very strong organic acids (acid groups ionized at pH 3.0) represent a significant portion of the total acidity (4--25%) in samples of organic matter isolated from two lakes, a landfill leachate, and a Krafft mill effluent. On the basis of model compound behavior and established complexation constants, these very strongly acidic groups are predicted to be the key to the formation of strong surface complexes between organic molecules and oxide surfaces. This prediction was confirmed for the sorption of aquatic natural organic matter (NOM) on to preformed iron oxide surfaces. A significant fraction of the carboxylic acidity in polymeric analogs to NOM is due to weak acids (which ionize above pH 8.0L If a portion of the weak acidity in aquatic NOM currently attributed to phenols were actually clue to carboxylic acids, significant discrepancies in the understanding of NOM behavior could be reconciled.