Selective recovery of Ag(I) from industrial wastewater using zeolite imidazolate framework-8: performance and mechanisms.

The recovery of silver from wastewater is of great significance due to its economic and environmental interest. In this work, zeolitic imidazolate framework-8 (ZIF-8) was chosen to adsorb Ag(I) from wastewater for the first time. The adsorption performance was assessed by adjusting the pH value, uptake time, initial concentration of Ag(I), as well as temperature. The saturated adsorption capacity for Ag(I) onto ZIF-8 can reach 446.7 mg·g-1, which shows that ZIF-8 not only possesses remarkable adsorption performance but also is superior to the reported adsorbents. The selectivity coefficients of ZIF-8 for Ag(I)/Cd(II), Ag(I)/Ni(II), and Ag(I)/Co(II) are 8.242, 8.315, and 136.3, respectively. The Sips adsorption model matches adsorption isotherms of Ag(I) onto ZIF-8 well, and the pseudo-second-order model is more suitable to illustrate the kinetics data. Thermodynamic experiment indicates that the adsorption process of Ag(I) is an exothermic reaction. Mechanism studies suggest that the redox reaction of Ag occur in the adsorption process. In addition, the study of recycling use indicates that the stable adsorption performance being maintained after recycle twice. Thus, a promising adsorbent is introduced to recover Ag(I) from wastewater in this work.