[Efficiency of Sediment Amendment with Zirconium-Modified Kaolin Clay to Control Phosphorus Release from Sediments in...

A zirconium-modified kaolin- clay (ZrMK) was prepared and used as a sediment amendment to control the release of phosphorus (P) from sediments in heavily polluted rivers under low dissolved oxygen (DO) condition. Results showed that the ZrMK exhibited excellent adsorption performance of phosphate in water. The phosphate adsorption capacity of the ZrMK increased with the increasing of loading amount of zirconium in the ZrMK. The phosphate adsorption capacity of the ZrMK increased with the increase of the precipitated pH value from 8 to 10, remained basically unchangeable with the increase of the precipitated pH value from 10 to 11, but decreased with the increase of the precipitated pH value from 11 to 12. The phosphate equilibrium adsorption data of the ZrMK can be better described by the Langmuir isotherm model than the Freundlich isotherm model when the ZrMK was prepared with the precipitated pH value 10. Sequential extraction of P from the phosphate-adsorbed ZrMK showed that most of phosphate-P bound by the ZrMK (about 84% of total P) existed in the form of the metal oxide P (NaOH-P) and residual P (Res-P), which was unlikely to be released under hypoxia and common pH (5-9) conditions. The fluxes of phosphate-P and total P (TP) from sediments into the overlying water column were greatly reduced with the adding of ZrMK to sediments under low dissolved oxygen conditions. The ZrMK-amended sediments exhibited much higher phosphate adsorption capacity than the original sediments, and the former had much lower phosphate adsorption/desorption equilibrium concentration (EPC,) than the latter. Our findings suggest that the ZrMK can be used as an efficient sediment amendment for controlling P release from sediments in heavily polluted rivers under low dissolved oxygen conditions.