Study On Granulation Method And Adsorption Effect Of Some High Efficient Adsorbents For Fluoride Removal

This paper focuses on the production of practical granular adsorbents for fluoride removal. Adsorption capacity and mechanical strength of granular adsorbent were taken into objective function. Granulation methods, fluoride removal performance as well as the adsorption mechanism of the adsorbent were researched for granular lanthanum alginate and granular iron-lanthanum complex hydroxides adsorbent.Granular lanthanum alginate was prepared by cross-link method. It was applied in fluoride removal and the results showed that the adsorption rate is fast and the adsorption kinetics was in accordance with second order reaction rate equation; the adsorption isotherm fitted Langmuir equation well; the adsorption process was mainly affected by pH and SO42-; the optimal pH was 4.0 and the maximum adsorption capacity was 197.2 mg/g. The adsorption mechanism of lanthanum alginate was ion exchange as seen from the studies. These adsorbents had good mechanical strength but could cause significant swelling. Granular iron-lanthanum complex hydroxides adsorbent was prepared using two methods, namely:extrusion and dropping method. Granular iron-lanthanum complex hydroxides adsorbent prepared by extrusion method was in bar shape. It adsorption rate was fast and the adsorption kinetics was in accordance with first order reaction rate equation; the adsorption isotherm fitted Langmuir equation well; the optimal pH range was 5-7, the maximum adsorption capacity was 12.1 mg/g at the optimal conditions. HCO3- and HPO42-affected the adsorption process largely. In column test the breakthrough volume of our adsorbent was much higher than that of activated alumina; the dynamic adsorption capacity was over 3 times of that of activated alumina. But the adsorbent's mechanical strength reduced a lot when soaked in water for a long time.Granular iron-lanthanum complex hydroxides adsorbent prepared by dropping method was in ball shape. Its adsorption rate was fast and the adsorption kinetics was in accordance with second order reaction rate equation; the adsorption isotherm fitted Langmuir equation well; adsorption process was maily affected by pH and SO42-, the optimal pH was 4, the maximum adsorption capacity was 30.1 mg/g on the optimal conditions. In column test breakthrough volume was 2326, which is 8-10 times of that of activated alumina. The adsorbent had good mechanical strength.Studies showed that granular lanthanum alginate had high adsorption capacity, but with high lanthanum element content, which lead to high application price. Granular iron-lanthanum complex hydroxides adsorbent prepared by extrusion method wasn't suitable for application because of its poor mechanical strength. Granular iron-lanthanum complex hydroxides adsorbent prepared by dropping method had good adsorption capacity and mechanical strength, so it had the potential of application.