TIME-DEPENDENT ADSORPTION IN NEAR COASTAL MARINE-SEDIMENTS - A 2-STEPMODEL

Many important physical and chemical processes occur at phase boundari es. The role of surface phenomena is frequently underestimated or over looked although surfaces play a significant role in many natural scien ce disciplines. Experimental data from the literature indicate that in adsorption from solution, most of the adsorbates move to the adsorben t surface in a relatively short time period. Actual adsorption equilib rium, however, may take longer to establish. in this study time variab le parametric experiments were performed with Co and a suspended mar:n e sediment sample. Two different time dependencies were observed: a ra pid step that reached equilibrium in 5-10 days, while a slower step co ntinued for more than 100 days. Observed behavior was simulated with a time-dependent model that differentiates the slow and fast steps. The fast step was considered to be due to diffusion of the adsorbate to t he external and macropore surface of the adsorbent and exchange at sur face sites, while the slow step was considered as diffusion of adsorba te into the adsorbent micropore capillaries where adsorptive binding o ccurs. (C) 1998 Elsevier Science Limited. All rights reserved.