Preparation and characterization of abandoned oyster shell-metal materials and their adsorption and mechanism of phosphorus in wastewater

Oyster shell was modified with Fe(Ⅲ) and Al(Ⅲ) (B-Fe-OS and B-Al-OS), and the modified products were calcined at 800 °C to prepare composites (Fe-OS and Al-OS). Analyses showed that CaCO3 was pyrolyzed to CaO under high temperature, and CaO chemically reacted with Al2O3 and Fe2O3 to form Ca2Fe2O5 and mayenite. And Fe(Ⅲ) and Al(Ⅲ) promoted the decomposition of CaCO3, especially B-Fe-OS, which reduced the pyrolysis peak of CaCO3 by 48 °C. The phosphorus removal tests showed that the saturation adsorption amounts of Fe-OS and Al-OS were 628.41 mg/g and 506.90 mg/g, respectively. SEM showed that a large amount of flocculent products were generated on the surface of composite materials after phosphorus removal. EDS and theory analysis proved they contained Ca3(PO4)2. The kinetic adsorption behavior of Al-OS and Fe-OS was fitting with Pseudo-second-order rate equation (R2 ≥ 0.999). The adsorption rate of Al-OS and Fe-OS was controlled by the outer film diffusion and the intra-particle diffusion together. The thermodynamic adsorption behavior of Al-OS and Fe-OS fitted Langmuir isotherm model (R2 ≥ 0.999). Analysis showed Al-OS and Fe-OS belonged to monolayer adsorption and they had strong ability to remove phosphorus.