Metal Organic Frameworks of ANA Topology as an Effective Adsorbent for Co(II) and Mn(II) in Solution

Long-lived radionuclides such as 60Co and 54Mn in radioactive waste water must be properly treated to protect the environment from long-term radioactive hazard. In this study, nine zeolite imidazole frameworks (ZIFs) were initially synthesized to investigate an effective adsorbent for Co(II) and Mn(II) in solution. Zeolite imidazole framework-14 (ZIF-14) with good performance was selected, and subsequent characterization and adsorption performance tests were conducted. The results show that ZIF-14 has good hydrothermal stability within 520 °C. Under the conditions of pH = 6.72, T = 303 K and the initial concentration of 500 mg·L–1, the saturated adsorption capacity for Co(II) and Mn(II) reached 148.55 mg·g–1 and 252.85 mg·g–1, respectively. The analysis of thermodynamic parameters shows that the adsorption process of ZIF-14 to Co(II) and Mn(II) is spontaneous and endothermic. The pseudo-second-order kinetic model, Langmuir isotherm model, and Boyd model are more in line with the adsorption process of Co(II) and Mn(II) by ZIF-14, which proves that the active sites on the surface of ZIF-14 are evenly distributed, and the adsorption process is single-molecule chemical layer adsorption. In addition, the liquid film diffusion dominates the adsorption rate during the adsorption process of Co(II) and Mn(II) by ZIF-14. ZIF-14 has good selectivity for cobalt and manganese in both high-concentration interference ion solution and multimetal ion solution with the same concentration. Moreover, ZIF-14 still has good adsorption performance after five times of elution.