Efficiency and mechanism for the control of phosphorus release from sediment by the combined use of hydrous ferric oxide, calcite and zeolite as a geo-engineering tool

In this research, the efficiency and mechanism for the suppression of phosphorus (P) liberation from sediment by the combined use of hydrous ferric oxide (HFO), calcite and zeolite as a geo-engineering tool were investigated. The results showed that the coexisting calcite enhanced the adsorption of phosphate onto HFO via the release of Ca2+ from calcite and the formation of phosphate-bridged Fe-P-Ca ternary complex on the surface of HFO. HFO/calcite/zeolite mixture exhibited good phosphate sorption performance, and the maximum phosphate sorption capacity was 35.9 mg P/g. The sorption of phosphate on HCZ could be primarily due to the surface adsorption of phosphate onto calcite and zeolite, the surface adsorption of phosphate onto HFO via the mechanisms of inner-sphere Fe-phosphate complex and phosphate-bridged Fe-P-Ca complex formation, and the precipitation of calcium phosphate. HFO/calcite/zeolite combined capping and amendment both can greatly cut down on the risk of the release of sedimentary P to the overlying water under the oxygen-poor condition, and the generation of a static layer with low concentrations of soluble reactive P and diffusive gradients in thin film-labile P in sediment was vital to the control of phosphorus liberation from sediment into the overlying water by these methods. Most (approximately 70%) of the total P bound by the HFO/calcite/zeolite combined capping layer existed in the form of moderately or highly stable P, which is not easy to be re-released under the circumstances of normal pH and reducing environment. Results of this work demonstrate that the combined used of HFO, calcite and zeolite as a geo-engineering tool is a sediment remediation strategy with a great application prospect for managing the internal loading of P in surface waterbodies.