Sorption of water-soluble oligomers on sediments

The adsorption and desorption of oligomers of nonionic poly(ethylene glycol) (PEG) and cationic poly(ethylenimine) (PEI) were measured on several sediments. These oligomers adsorb strongly, particularly at low aqueous concentration, even though they are water-soluble. The adsorption isotherms have a Langmuir shape. Sorption capacity correlates with the cation-exchange capacity for PEI and the sediment clay content for PEG but not with the sediment organic carbon content. Sorption increases for a given oligomer with increasing molecular weight. Lowering the solution pH increases PEI adsorption and decreases PEG adsorption. Adsorption/desorption reversibility is less than 50% at high aqueous concentrations and diminishes to 10% or less at low aqueous concentrations. Additional study results are discussed.