COMPETITIVE ADSORPTION, DISPLACEMENT, AND TRANSPORT OF ORGANIC-MATTERON IRON-OXIDE .2. DISPLACEMENT AND TRANSPORT

The competitive interactions between organic matter compounds and mine ral surfaces are poorly understood, yet these interactions may play a significant role in the stability and co-transport of mineral colloids and/or environmental contaminants. In this study, the processes of co mpetitive adsorption, displacement, and transport of Suwannee River na tural organic matter (SR-NOM) are investigated with several model orga nic compounds in packed beds of iron oxide-coated quartz columns. Resu lts demonstrated that strongly-binding organic compounds are competiti vely adsorbed and displace those weakly-bound organic compounds along the flow path. Among the four organic compounds studied, polyacrylic a cid (PAA) appeared to be the most competitive, whereas SR-NOM was more competitive than phthalic and salicylic acids. The transport of SR-NO M is found to involve a complex competitive interaction and displaceme nt of different NOM subcomponents. A diffuse adsorption and sharp deso rption front (giving an appearance of irreversible adsorption) of the SR-NOM breakthrough curves are explained as being a result of the comp etitive time-dependent adsorption and displacement processes between d ifferent organic components within the SR-NOM. The stability and trans port of iron oxide colloids varied as one organic component competitiv ely displaces another. Relatively large quantities of iron oxide collo ids are transported when the more strongly-binding PAA competitively d isplaces the weakly-binding SR-NOM or when SR-NOM competitively displa ces phthalic and salicylic acids. Results of this study suggest that t he chemical composition and hence the functional behavior of NOM (e.g. , in stabilizing mineral colloids and in complexing contaminants) can change along its flow path as a result of the dynamic competitive inte ractions between heterogeneous NOM subcomponents. Further studies are needed to better define and quantify these NOM components as well as t heir roles in contaminant partitioning and transport.