Adsorption Kinetics for Urban Rainfall-Runoff Metals by Composite Oxide-Coated Polymeric Media

Abstract

A manganese oxide-coated polymeric media (MOPM) utilized in sorptive filtration systems as a rainfall-runoff or snowmelt unit operation and process media was characterized using scanning electronic microscopy and adsorption kinetics were studied using a flow-through batch reactor. Results indicated the MOPM adsorption kinetics can be described as a fast adsorption reaction occurring within 30 min followed by a slower reaction that continued from 5 to 15 h, as a function of initial pH and sorbent dosages. A potential driving kinetic model was developed based on an elementary second-order rate law. Modeled results were compared to experimental data using this model and a series of comparative kinetic models. Manganese oxide surface morphology and the ability of a parabolic diffusion model to predict the adsorption kinetics of MOPM suggest diffusion-controlled adsorption for divalent heavy metals on MOPM. Based on a goodness of fit test, the potential driving model best represented the experimental data. Using the potential driving model, it was found that rate constants increased with increasing solution pH, but were independent of sorbent dosages. Results indicated that metal ions with the highest adsorption affinity had the highest rate constants. Observed porosity, the excellent fit of the potential driving model, and breaks in Elovich model plots all suggest a complex adsorption mechanism. Results suggest MOPM can be an effective media for rainfall-runoff and snowmelt metal adsorption.