Fluoride Removal By Modified Granular Activated Alumina And Its Regeneration

Fluoride is an important element for human health. The proper level of fluoride is good for the formation of healthy teeth and bones, but an excess of intake of fluoride is harmful to human body. Thus, it is of significance to develop effective and economical defluorination methods. Through comparing the present defluorination methods, adsorption by activated alumina is an effective and mature method for defluorination, but the adsorption capacity of activated alumina is not high enough, so it is necessary to be modified in order to attain a higher adsorption capacity. So this paper studied the modification of activated alumina and defluorination properties, in addition, regeneration of the modified adsorbent was also studied in this paper.This paper had researched the 1-2 mm activated alumina modified by three kinds of salt solution (Al2(SO4)3,Fe2(SO4)3,FeCl3 solution respectively), and the modification method was direct immersion method. The influence of adsorption capacity of the salt solution concentration and modification time was also researched. The results showed that the concentration of salt solution and modification time had obvious effect to the adsorption capacity of the modified activated alumina. The best modification time of the three modified adsorbents was 3-6 h, the best concentration of Al2(SO4)3,Fe2(SO4)3N FeCl3 solution were 2.5%,3.0%,3.5% respectively. The results of defluorination experiments showed that the static capacity of modified adsorbents increased 4.0-7.0 times, the dynamic breakthrough volume was 1.5-2.0 times of unmodified activated alumina. The results of dynamic experiments showed that the activated alumina modified by Al2(SO4)3 and FeCl3 solution had serious dissolution of metal ions, while the activated alumina modified by Fe2(SO4)3 solution had good effect of defluorination and had no dissoloution Of metal ion. Comparing with other two modified adsorbents, the activated alumina modified by Fe2(SO4)3 solution had obvious advantages for fluoride removal. The static and dynamic experiments were studied in order to further investigate the defluorination performance of modified activated alumina by Fe2(SO4)3 solution. The results of the static experiments showed that there were some factors influencing the adsorption capacity of this modified adsorbent, including fluoride concentration, co-existing ions, pH values of the solution and so on. The results of the dynamic experiments showed that the defluorination effect can be increased clearly by modulating the pH value of the initial fluoride solution, and the breakthrough volumn ratio was over 1400 times when the pH value of the intial fluoride solution was 5.5. For the regeneration of the saturated modified activated alumina, this paper researched the regeneration conditions by using NaOH solution as the desorption solution and Fe2(SO4)3 solution as the activated solution, and the conditions including desorption solution concentration, desorption time and the effect of recycling times. The results showed that the best regeneration scheme was:1.0% NaOH solution desorption for 6 h-3.0% Fe2(SO4)3 solution activation for 6 h, the average breakthrough volume of the modified adsorption had no decline after continuous running 9 cycles.The activated alumina modified by Fe2(SO4)3 solution had excellent adsorption performance in the evaluation in the paper and it has a good application prospect.