Synthesis and evaluation of zirconia/magnetite/zeolite composite for controlling phosphorus release from sediment: A laboratory study

Although the conventional zirconium-based solid-phase phosphorus (P)-inactivating agents (ZrPIAs) have high potential for controlling P release from sediments in aquatic systems, they are difficultly retrieved from sediments after their application. Therefore, it is very necessary to develop new ZrPIAs that can be readily retrieved from sediments after their application. In this study, a novel magnetic ZrPIA, i.e., zirconia/magnetite/zeolite composite (ZMZ) was prepared, characterized and used as a sediment amendment to control the release of P from sediments. The adsorption performance and mechanism of phosphate on ZMZ were studied using batch experiments and XPS analysis. The impact of ZMZ addition on the releasing flux of P from sediments to the overlying water as well as on the fractionation and bioavailability of P in sediments was studied using microcosm incubation experiments. In addition, the stability of P captured by ZMZ was also investigated. Results showed that ZMZ exhibited high adsorption ability towards phosphate, with a maximum phosphate adsorption capacity of at least 4.1 mg P/g, and phosphate adsorption onto ZMZ was mainly controlled by inner-sphere complex formation mechanism. The ZMZ addition greatly decreased the releasing flux of P from sediments into the overlying water in anoxic environment, with a DTP (dissolved total P) reduction efficiency of 61.8-97.8%. Moreover, the added ZMZ could immobilize mobile P in sediments by changing P species from Na2S2O4/NaHCO3-extractable P (BD-P) to NaOH-extractable P (NaOH-rP) and residual P (ReseP). Furthermore, the bioavailability of P in sediments could be reduced by the addition of ZMZ. The stability evaluation of P captured by ZMZ after its application showed that a majority of P adsorbed by ZMZ existed in the form of NaOH-rP and ReseP, which were difficult to be re-released into the water column under common pH (5-9) and reducing condition. In summary, the above results demonstrate the high potential for the application of ZMZ as an amendment in the control of P release from sediments.