Fluoride Removal From Drinking Water By Zr-Modified Granular Activated Alumina

To improve the adsorption capacity and to expand the application range of pH were set as the main objectives, the modification of granular activated alumina (GAA) by ZrOCl2·8H2O and the adsorption performance of the modified adsorbent named Zr-GAA were studied in this paper. What’s more, the effect of the particle sizes on the adsorption performance of Zr-GAA was investigated.In this article, effects of modifying concentration、modifying time and soild-to-liquid ratio on defluorination of Zr-GAA were studied. When the modifying concentration was 2.0g/L, modifying time was 12h and the soild-to-liquid ratio was 1:20, the optimum conditions were obtained. When the equilibrium concentration of fluoride was 1.0mg/L, the adsorption capacity of Zr-GAA was 3.50mg/g.The results of ICP showed that the amount of Zr loading to the surface of GAA was 32.58mg/g.The effects of contact time, dosage, pH, initial fluoride concentration, co-existing ions, and other factors were studied in the batch experiments, and then the adsorption kinetics, adsorption isotherm and controlling steps were analyzed. The results showed that the adsorption of F on Zr-GAA mianly occurred in the first 60min, and reached steady in 180min, the adsorption rate increasd at least by 25% compared with GAA. In order to make the residual F concentration less than 1.0mg/L in the initial concentration of 5.15mg/L, the dosage of GAA was 4 times of Zr-GAA, so the adsorption capacity of Zr-GAA had been greatly improved. The advantage of GAA was outstanding, especially in the process of treating the solution with low concentration of fluoride. When the initial pH of solution was in the range of 4.5-9.7, the water treated by Zr-GAA could still meet the requirements of drinking water, but the range of GAA was 4.5-7.8, so the conclusion that the application range of Zr-GAA was expanded was obtained. SO42-, HCO3- had an adverse effect on the adsorption capacity of Zr-GAA for F. The pseudo-second-order model, Langmuir and D-R adsorption isotherms could better fit the adsorption of Zr-GAA, the process of liquid film diffusion was the controlling step.The effect of the height of Zr-GAA packed in the column on the break--through time was investigated in the continuous experiments, and the adsorption capacity of per unit volume of Zr-GAA was obtained. The results showed the higher of the height of Zr-GAA packed in the column, the longer of the breakthrough time and the greater of the adsorption capacity for fluoride as well as the removal rate of fluoride. When the column packed with Zr-GAA was 25.4cm, the breakthough time was 195h, the adsorption capacity for fluoride was 2.80mg/g and the removal rate of fluoride was 97.68%. Bohart- Adams model predicted the adsorption capacity for fluoride onto Zr-GAA was 45.45mg/LCompared with the adsorption performance of Zr-GAA with three different particle sizes, namely 0.513、0.338、0.178mm, the results showed that the adsorption rate, the adsorption capacity and the diffusion coefficient increased when the particle size decreased.And the particle size also had an effect on the adsorption potential (E), the value of E got bigger with the decrease of particle size, and the chemical adsorption was more obvious in the smaller particle size.By the analysis of the paper, the adsorption performance of Zr-GAA is excellent for defluoridation, and the improvements of the adsorption capacity and the application range of pH are obvious. So Zr-GAA has a good possibility for pratical application.