Phosphorus adsorption on natural sediments: Modeling and effects of pH and sediment composition

Abstract

The classic Langmuir isotherm equation was modified to describe phosphorus (P) adsorption on P-polluted sediments. The P adsorption characteristics of six sediment samples from Chinese Taihu Lake were studied by short-term isotherm batch experiments and related to sediment composition. The maximum P adsorption capacities (PAC) and P-binding energy constant (k) were obtained by nonlinearly fitting sorption data using the modified Langmuir isotherm model. Native adsorbed exchangeable phosphorus (NAP), the zero equilibrium P concentration value (EPC 0), and partitioning coefficients ( K p) were subsequently calculated by corresponding formulae. K p and PAC were linearly related to the contents of active Fe and Al in sediments by least squares regression analyses ( R 2 ≈ 0.9 for both). The effect of pH in a wide range on adsorption process was investigated and H 2PO 4 − was presumed to be the preferential sorption species in overall sorption process. The fact that the amount of P sorbed and zeta potential of sediment particles have no necessary relationship reveals that a strong contribution to the P binding still comes from a ligand-exchange process on the Me–OH 2 + and Me–OH sites rather than electrostatic attraction. In addition, the influence of oxidation–reduction potential (ORP) was investigated and discussed and the dual nature of sediments as a pool or source of P in natural waters was evaluated in site T1–T4.