Phosphorus removal by in situ sprayed ferric chloride in Dianchi Lake: Efficiency, stability, and mechanism

In this work, ferric chloride was applied to remove phosphorus from natural water bodies of Dianchi Lake. The feasibility and efficiency of phosphorus removal using ferric chloride are reported. The factors that influence the stability of Fe-P coprecipitates formed during the phosphorus removal process (including temperature, pH, coexisting ions, fast mixing speed (FMS), and fast mixing time (FMT)) were studied in detail. Results show that ferric chloride can efficiently remove phosphorus, and Fe-P coprecipitate exhibits high stability. In a water temperature range of 10–35 °C and pH range of 3–11, the phosphorus in the Fe-P coprecipitates is stable and is not released. The maximum phosphorus release efficiency is 9.2% at a pH of 3, and 16.10% at a pH of 11. The presence of Ca2+ and CO32− has little effect on the stability of Fe-P coprecipitates, and the differences in fast mixing speed and time have little effect on the stability of Fe-P coprecipitates. Furthermore, on the basis of Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis, adsorption and ligand exchange were identified as the main phosphorus removal mechanisms by ferric chloride. These findings demonstrate that ferric chloride is a promising candidate for highly efficient and stable phosphorus removal from water of Dianchi Lake.