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 Cs-effect phenomenon, namely, the experimentally measured partition coefficient (Kp) value of a given system decreased with increasing the sorbent concentration (Cs), was observed in a number of adsorption systems. Classical Langmuir model cannot predict the Cs-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 Cs because of the existence of adsorbent particle–particle interactions. A semi-empirical Cs-dependent function of partition coefficient was derived, and it can predict the Cs-dependence of partition coefficient for both organic compounds and heavy metals.