Performance Of Fluoride Removal In Drinking Water By Fe(â…¢)-modified Heterozygous Absorbent

Fluorine is an essential trace element in human body, suitable amount of the fluorine is good for human health. However fluorine over intake will cause a kind of diseases generally called "fluorosis", which leads to the fluorine osteopathy, fluorine spot tooth and so on. Drinking water containing high concentration of fluoride ions is the primary reason. As human pay more attention to the environment and health, fluorine drinking water gets more and more attention. It is urgent to develop novel and efficient technology about eliminating the fluorine.Fe(Ⅲ)-modified macroporous sulfonic acid resins and Fe(Ⅲ)-loaded cotton cellulose adsorbents were separately used as the absorbents in the paper. The adsorbents were characterized by FTIR spectrum and X-ray diffraction (XRD). Batch experiments were carried out to investigate the adsorption potential. The results were simulated with dynamics models and thermodynamics models.The static experiments indicated that the two absorbents all have a good adsorption performance. The adsorption of fluoride on Fe(Ⅲ)-modified resins and the Fe(Ⅲ)-loaded ligand exchange cotton cellulose adsorbents is independent of pH value, and the saturated adsorption capacity increase with the increase of temperature. The static saturated adsorptive capacity of the former achieves 2.6006 mg·g-1 in the 298K and the latter is 9.0995 mg·g-1. Langmuir and the Freundlich isotherm can describe the fluorine adsorption characteristic well. The existence of interfering ions in the solution have no influence on the F- adsorption.The Adsorption kinetics showed that the fluoride adsorption onto Fe(Ⅲ)-modified macroporous sulfonic acid resin followed the Elovich dynamic model and the pseudo-second order kinetic equation well. The pore diffusion is not the only control step of adsorption rate. Both extra-and intra-particle diffusion contributed to the adsorption process. The Boyd dynamic equation analysis showed that diffusion external diffusion is the primary control step. The adsorption behavior onto Fe(Ⅲ)-loaded cotton cellulose adsorbents followed the pseudo-first order kinetic equation and the pseudo-second order kinetic equation well. The pore diffusion is not the only control step, Both extra-and intra-particle diffusion contributed to the adsorption process. And the intra-particle diffusion is the primary control step.The thermodynamic study indicates that the positive value of△H shows an endothermic process and the negative value of△G shows an spontaneous process. The positive value of△S indicates the adsorption is an entropy impressing process and the increased randomness at solid/solution interface during the adsorption processes.The breakthrough curves were eliminated with the column adsorption experiment. The column adsorption experiment indicated that the penetration of the adsorption column bed speeds up as the velocity increases. As to Fe(III)-modified macroporous sulfonic acid resins, when the flow velocity increases from 20 BV·h-1 to 40 BV·h-1, the breakthrough bed volume drops from 102BV to 92 BV; as to the Fe(III)-loaded cotton cellulose adsorbent, when the flow velocity increases from 20 BV·h-1 to 40 BV·h-1, the breakthrough bed volume drops from 154BV to 146BV.