Effect of surface heterogeneity on phosphorus adsorption onto mineral particles: experiments and modeling

Purpose: Adsorptive interaction at the solid-water interface plays an important role in the fate and behavior of phosphorus (P) in rivers and lakes and the resulting eutrophication. This study aims to investigate the contributions of heterogeneous morphology to P adsorption onto mineral particles. Materials and methods: The dominant minerals in Yellow River sediment, quartz, k-feldspar, and calcite are investigated with adsorption experiments and microscopic examinations. Taylor expansion is applied to quantitatively characterize the heterogeneous surface morphology. Results and discussion: The results reveal that locally concave or convex micro-morphology characterized by the second derivative term of the Taylor expansion, F₂, can be related to adsorption capacity due to its effect on surface-charge density and distribution. The distribution of adsorbed P as a function of F₂ was determined for selected particles composed of each of the pure minerals and was fit to a Weibull distribution. Each mineral was characterized by F_2a, the weighted average value of F₂, and Weibull distribution factors, and correlated with sorption isotherms. The developed relationships were used to accurately predict adsorption onto individual particles as well as pure mineral samples. Conclusions: Mineral particles have complex surface morphology, which affects the interface P adsorption. Micro-morphological characterization of F₂ and F_2a can be used to predict adsorption onto the pure minerals, and this study provides physical basis for predicting adsorption on sediment particles composed of these minerals.