Sorption kinetics of organic chemicals: Methods, models and mechanisms

Rate-limited or, nonequilibrium, sorption of organic chemicals by natural sorbents (i.e., soils, sediments, and aquifer materials) has been a topic of interest for quite some time. The impact of nonequilibrium sorption on transport of organic chemicals in the subsurface has recently come under increased scrutiny as groundwater contamination has become a major issue. The purpose of this paper is to provide a brief review of the rate-limited sorption of organic chemicals by natural sorbents. The proposed processes held responsible for nonequilibrium sorption will be presented, as will a discussion of recent experiments whose results provide elucidation of rate-limiting mechanisms. Several models have been proposed to simulate sorption kinetics, and the transport of solutes influenced by nonequilibrium sorption; these will be reviewed. A large array of techniques are available for the study of sorption kinetics. However, much of this work has been oriented towards the study of inorganic chemicals. We will discuss two techniques that, in addition to the standard batch time study, have received the greatest amount of use in investigating nonequilibrium sorption of organic chemicals.