Zirconium loaded on tannin foam for efficient adsorptive removal of fluoride at low concentration in a wide pH range

Recently, fluoride (F-) pollution in groundwater and surface water is widespread all around the world. Although adsorption is regarded as one of the simplest and cost-effective processes for removing F-, the removal efficiency of F- has always been restricted by the low adsorption ability and poor stability of adsorbent. In this study, zirconium (Zr(IV)) loaded on tannin foam (TF) was synthesized and utilized as adsorption material for efficient removal of F-. It was found that the amount of Zr loaded on TF affected the adsorption of F- and the optimal mass ratio of Zr/TF was 0.25. Through static adsorption experiments, the optimal material exhibited highly efficient adsorption performance for different concentrations of F- (2.0-20 mg L-1), with the removal efficiency as high as around 80% in a wide pH range of 3.0-10.0. Co-existing ions could reduce the adsorption of F(- )on TF-Zr, especially CO32- with the F(- )removal efficiency of only 38.4%. Moreover, the adsorption data were highly adjacent with the Langmuir adsorption model with monolayer coverage and pseudo-second-order kinetic model. The calculated maximum adsorption was 10.2 mg g(-1) at 25 degrees C, which was higher than most of the other forms of materials. The thermodynamics of F- adsorption was found to be a spontaneous and exothermic process. It was identified that the highly effective adsorption performance was ascribed to the powerful complex adsorption between Zr(IV) and F-, porous properties of tannin foam matrix, and exceptional stability of Zr(IV) as well. Finally, dynamic adsorption experiment revealed that 3.8 g Zr-TF material could continuously remove 11.02 L water contaminated by low concentration (2.0 mg L-1) of F with adsorption capacity of 5.8 mg g(-1). The present work could provide an alternative material for effective removal of fluoride in aqueous solution.