Immobilization of phosphorus from water and sediment using zirconium-modified zeolites

Adding sorbents to sediments has been suggested as an effective technology for contaminated sediment remediation. In this study, a zirconium-modified zeolite (ZrMZ) was prepared, characterized, and used as a sediment amendment to control phosphorus (P) release from eutrophic lake sediments. The efficiency of ZrMZ in immobilizing P from water and sediments was investigated through a series of experiments. The phosphate adsorption capacity for ZrMZ decreased with increasing water pH. The adsorption of phosphate on ZrMZ followed a pseudo-second-order kinetic model. The equilibrium adsorption data of phosphate on ZrMZ could be well described by the Langmuir isotherm model with a maximum monolayer adsorption capacity of 10.2 mg P/g at pH 7 and 25 °C. Sequential extraction of P from the phosphate-adsorbed ZrMZ suggested that most of P bound by ZrMZ existed as the NaOH extractable P (NaOH-P) and residual P (Res-P) and was unlikely to be released under natural pH and reducing conditions. The addition of ZrMZ into sediments reduced the inorganic P activity in the sediments by transforming bicarbonate-dithionite extractable P (BD-P) to NaOH-P and Res-P. The contents of bioavailable P such as water-soluble P (WS-P), NaHCO3 extractable P (Olsen-P), and algal available P (AAP) in sediments reduced after the sediments were mixed with ZrMZ, making P in the sediments more stable. The addition of ZrMZ into sediments significantly reduced the releasing flux of P from the sediments to the water column under different conditions. Results of this study indicate that the ZrMZ is a promising sediment amendment for controlling the internal P loading of lake sediments.