Uranium (U) ion contamination in aquatic systems has received considerable attention worldwide. In this paper, an adsorption material was synthesized with Fe/Ca-based phosphate (CFB-PM) by a sol-gel method. The effect of pH, reaction time and initial concentration of U ions on its capacity of removing U ions from aqueous solution was investigated by static batch experiments. Comparative studies of U ion removal by CFB-PM with four sorbents, namely: nano zero-valent iron (nZVI), hydroxyapatite (HAP), hydroxyapatite-loaded nano zero-valent iron (HAP@nZVI) and high basicity steel slag loaded hydroxyapatite (HBSS@HAP), were performed. Results showed that U ion adsorption capacity of CFB-PM was better than that of nZVI, HAP, HAP@nZVI and HBSS@HAP. The adsorption capacity showed a decreasing order as: CFB-PM (643.34 mg/g) > HAP (549.86 mg/g) > HBSS@HAP (321.82 mg/g) > HAP@nZVI (153.62 mg/g) > nZVI (102.65 mg/g). SEM-EDS examination suggested that the adsorbed U ions were mainly in the form of spheres, sheets or petals on the surfaces of CFB-PM. XRD detection revealed several U-bearing mineral phases (i.e. Ca(UO2)2(PO4)2·3H2O, HPUO6·4H2O and (UO2)3PO4·4H2O). The U ion adsorption behaviors were further explored by FTIR spectroscopy. The uranium ion adsorption process of CFB-PM could be well described by quasi-second-order adsorption kinetics model and the Langmuir adsorption isotherm model. The separation coefficient (RL) was close to zero, indicating that U ion adsorption was dominated by single-layer chemisorption. The findings reported in this study have implications for applying the synthesized material for remediation of U ion-contaminated groundwater.
High dispersions of nano zero valent iron supported on biochar by one-step carbothermal synthesis and its application in chromate removal
