Phosphorus adsorption onto clay minerals and iron oxide with consideration of heterogeneous particle morphology.

Particle morphology plays an important role in solid-water interface adsorption, which affects the fate and behavior of phosphorus (P) in rivers and lakes and the resulting eutrophication. In this paper, three minerals including kaolinite, montmorillonite and hematite were considered to investigate the contributions of particle morphology to P adsorption using adsorption experiments and microscopic examinations. The Taylor expansion method is applied to quantitatively characterize the heterogeneity of surface morphology. The results reveal that local concave or convex micro-morphology characterized by the second order term of Taylor expansion F2, can affect the local adsorption capacity due to its effect on the distribution of surface charge and reactive sites. Moreover, the adsorbed P at different F2 here fits to a Weibull distribution, which can further define the representative average adsorption onto individual particles. A weighted average morphology factor F2a is derived to characterize the surface heterogeneity, and correlated with average P adsorption of particular mineral particles. In addition, the Sips model can successfully fit the experimental data of different minerals, and the heterogeneity parameters γ and adsorption capacity Qm in the model are proved to be functions with the basic mineral properties, including particle size, surface site density and morphology characterization as well. It is concluded that the complex surface morphology plays a significant role in particle adsorption and the morphological role need to be considered in the adsorption model in order to better describe the adsorption in system with heterogeneous solid surface.