Experimental study on the adsorption and interaction of P and Cd in polluted sediment from Dongting Lake

A series of experiments was performed to elucidate the effects of the adsorption and interaction of different concentrations of P and Cd on the availability of P and Cd. First, the sediments before and after maturation were subjected to X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared (FTIR) spectroscopy. The results revealed that the composition and main components of the sediment were unchanged by maturation. The adsorption results fitted by the Freundlich equation revealed that the maximum concentration of Cd in the sediment changed from 979.12 mg/L to 980.92 mg/L and 1215 mg/L after the addition of 1 mg/L and 2 mg/L P, respectively. The maximum concentration of P in the sediments increased from 397.57 mg/L to 403.19 mg/L and 422.89 mg/L after the addition of Cd concentrations of 5 mg/L and 50 mg/L, respectively. A batch experiment was subsequently performed with multiple groups of P and Cd at the same concentration. The results revealed that the content of available Cd was the highest when the content of P was 180 mg/kg and that the content of available P was the highest when the content of Cd was 1 mg/kg. However, when the concentrations of P and Cd exceeded a certain level, Cd₃(PO₄)₂ precipitated. Finally, the experimental results were reverified by XPS, and the results revealed that the contents of P and Cd in the sediments increased through adsorption and precipitation between P and Cd.