Study On The Fluoride Removal With Activated Alumina Modified With Two Salts And Its Regeneration

A simple and efficient modified method for activated alumina was established. According to the results of static experiments, the adsorption effect of activated alumina modified with Fe2(SO4)3 and Al2(SO4)3 was best. The adsorption characteristic of fluoride in water on Fe2(SO4)3-Al2(SO4)3-MAA, and the effect of pH of fluoride solution and co-existing ions on adsorption of F-was studied in the paper. BET, SEM and XRD were performed to characterize activated alumina before and after modification. The regeneration method of Fe2(SO4)3-Al2(SO4)3-MAA was studied. The main results were summarized as following:1. According to the results of single-factor experiment and orthogonal experiment, the adsorption effect of activated alumina modified with Fe2(SO4)3 and Al2(SO4)3 was best. The best modification condition:the activated aluminas was soaked in 0.2% Fe2(SO4)3 solution for lh with a solid/solution ratio of 1:5 and then soaked in 0.5%Al2(SO4)3 solution for 0.5h with a solid/solution ratio of 1:5.2. The adsorption characteristic of fluoride in water on Fe2(SO4)3-Al2(SO4)3-MAA was studied. The fluoride adsorption kinetics on the modified activated alumina was well described by the pseudo-second-order kinetic model. The fluoride adsorption by modified activated alumina was consist with the Langmuir model. The maximum sorption capacity of modified activated alumina for fluoride was 6.25mg/g at 298K, significantly higher than activated alumina. During the adsorption, △G0<0, △H0>O, △S0>0. It indicated that the adsorption thermodynamics of fluoride is a spontaneous and endothermic process.3. The effect of pH of fluoride solution and co-existing ions on adsorption of F- was studied in the paper. Maximum fluoride removal occurred at pH 6. Fluoride sorption was mainly influenced by the presence of PO43-. NO3-, Cl- and SO42- had little influence on fluoride sorption onto Fe2(SO4)3-Al2(SO4)3-MAA.4. Activated alumina was analyzed through BET, SEM and XRD. The results of BET and SEM showed that, the surface area and the number of pore of activated alumina was increased after modified. After adsorption experiment of fluoride, the surface area of Fe2(SO4)3-Al2(SO4)3-MAA was decreased. The surface of adsorbents became smooth and compact. According to the results of XRD, the crystal structure of activated alumina was not changed after modified with Fe2(SO4)3 and Al2(SO4)3.5. According the results of safety evaluation, the solution adsorption by Fe2(SO4)3-Al2(SO4)3-MAA had no dissolution of metal ion. This showed that it was safe defluorination by Fe2(SO4)3-Al2(SO4)3-MAA.6. The regeneration method of Fe2(SO4)3-Al2(SO4)3-MAA was studied. The best regeneration condition:the saturated modified activated alumina was desorbed in 0.5mol/L NaOH solution for 2h with a solid/solution ratio of 1:5, and then activated in Fe2(SO4)3 and Al2(SO4)3 solution.