The effect of sorbent concentration on the partition coefficient of pollutants between aqueous and particulate phases

During studying the distribution of pollutants between the aqueous and particulate phases, an anomalous C-s-effect phenomenon, namely, the experimentally measured partition coefficient (K-p) value of a given system decreased with increasing the sorbent concentration (C-s), was observed in a number of adsorption systems. Classical Langmuir model cannot predict the C-s-effect. In this paper, a surface component activity (SCA) model was proposed, which suggests that surface component (adsorption site or adsorbed solute) activity coefficient is a function of C-s because of the existence of adsorbent particle-particle interactions. A semi-empirical C-s-dependent function of partition coefficient was derived, and it can predict the C-s-dependence of partition coefficient for both organic compounds and heavy metals. (C) 2011 Elsevier B.V. All rights reserved.