Natural siderite and calcium-derived Siderite/Ca composites for wastewater phosphate adsorption: Preparation, properties and mechanism

Abstract

The effective removal of phosphate from wastewater and prevention of eutrophication of water bodies are of great significance. This study develops and compares the phosphorus removal performance of natural siderite with three different modification methods: thermal activation, hydrothermal treatment, and surface precipitation. The calcium-modified siderite composite (SID-Ca) exhibited excellent phosphorus removal performance for low to medium concentration phosphate wastewater (PO₄^3--P < 15 mg/L), with a maximum adsorption capacity of 33.4 mg/g, which was 7.4 and 5.3 times higher than that of natural siderite (SID) (4.51 mg/g) and hydrothermally treated siderite (SID-H) (6.28 mg/g), respectively. SID-Ca did not show significant differences in adsorption performance at high levels of co-existing ions (SO₄^2-, NO₃^-) at 500 mg^/L. Following characterisation by XRD, XPS, FTIR and MAPPING, it was concluded that the phosphorus removal mechanism of the SID-Ca composites was primarily the inner complexation in ion exchange and ligand exchange. By leveraging the exceptional stability and low cost of natural siderite to develop a modified siderite using straightforward co-precipitation, a novel approach for phosphate adsorption in wastewater was established, and its removal mechanism was elucidated.