Preparation Of Composite Oxide Adsorbent For Recovery Of Iron And Aluminum From Red Mud And Its Fluorine Removal Performance

Fluoride is one of the few chemicals that has a significant impact on the drinking water.The presence of fluorine in drinking water is beneficial to the production and maintenance of healthy bones and teeth when its content is within permissible limits,while excessive intake of fluoride causes dental or skeletal fluorosis.According to the World Health Organization(WHO)guidelines,the upper limit of fluoride concentration in drinking water is 1.5 mg/L.In the drinking water health standards of China,the standard of fluoride concentration is below 1.0 mg/L.Adsorption methods are generally considered attractive for defluoridation because of its effectiveness,ease of operation,and economical efficiency.Nevertheless,some limitations such as high cost or low adsorption capaticy of the materials may be presented during the defluoridation process.To solve this problem,in this paper,the composite oxide adsorbent was prepared by using iron and aluminum recovered from red mud as the main raw material.Iron and aluminum are the main raw materials for the preparation of adsorbents from the red mud leached.The results showed that under the conditions of 3 mol/L HCl with L/S ratio 16:1 mL/g at 95? for 1.5 h,the leaching ratio of iron was 95.4%,while that of aluminum was 66.7%.After the acid leaching,the crystal phase of hematite disappeared and was completely leached by hydrochloric acid.We synthesized a Fe-Al composite oxide adsorbent which used the iron and aluminum as the main raw materials from the red mud leached.The optimum conditions of preparation:the molar ratio of Fe3+/Al3+ was 1:1,and the pH value was 7.5.Through the analysis of its characterization,it can be seen that the Fe-Al adsorbent was amorphous and the surface was rough with different sizes.The BET surface area and average pore diameter of the adsorbent were 283.3 m2/g and 2.4 nm,respectively.A Fe-Al-La adsorbent with high fluoride removal performance was prepared on the basis of Fe-Al adsorbent.The optimum conditions of preparation:the molar ratio of Fe3+/Al3+/La3+ was 2:2:1,and calcination temperature at 80?.Through the analysis of its characterization,it can be seen that the Fe-Al-La adsorbent was amorphous,and the surface of adsorbent was rough and composed of the aggregates of amorphous particles with different sizes.The BET surface area and average pore diameter of the adsorbent are 371.47 m2/g and 10.2 nm,respectively.Batch sorption experiments were conducted to evaluate the fluoride removal performance,and the results showed that the composite was fitted well with the Langmuir isotherm and pseudo-second-order kinetic model.The Fe-Al-La adsorbent showed high fluoride removal efficiency in a wide range of pH(3-9),and the maximum adsorption capacity was 74.07 mg/g.The FT-IR and XPS analyses showed that the hydroxyl group of the adsorbent is involved in the process of fluoride removal.All metals were present as trivalent form and participate in the removal of fluoride.The adsorption mechanisms for fluoride were electrostatic interaction and ion-exchange.