Experimental Study On Treating High Fluorine-containing Water By Synthesizing LDH In Situ

Layer double hydroxide(also called LDH) has similar laminated structure as brucite and its anions between layers can be easily exchanged, so it has specially excellent anions-exchanging properties, which has been extensively applied into catalyst preparation, compound materials synthesizing, biological medicine and environment engineering.Systematic study is carried out on the influencing factors and better reaction conditions of treating high fluorine-containing water by synthesizing LDH in situ, and research of elementary reaction mechanism and discussion of secondary pollution probability is also included.Single factor experiments have been done to investigate the impacting rules of Mg/Al molar ratio, pH value, time and temperature on treating high fluorine-containing water by synthesizing LDH in situ and their controlling methods. Based on the results, orthogonal experiments are designed to obtain better effective experimental conditions for this method, which has been confirmed as follow: Mg/Al molar ratio 2:1, temperature 50°C and pH value 9.5. The Fluorine removal efficiency under this condition can reach above 78%. Then by XRD, FT-IR analysis, elementary reaction mechanism has been presented. It's concluded that the remove of Fluorine is mainly by intercalation of F" anions into LDH layers, and LDH synthesizing in situ and intercalation of F" is two separate step in the whole process. Finally, the Fluorine-containing products of this process are testing for the Fluorine-holding property and the Fluorine-removing performance of three methods, synthesizing LDH in situ, aluminium chloride and pure LDH products, is compared. Results indicate that after LDH containing-Fluorine being dried under 70℃, the stability of F" anions intercalated is greatly increased and hardly induce the environmental secondary pollution. Comparing aluminium chloride, the Fluorine removal efficiency by synthesizing LDH in situ is a little lower, but the solid products with a better performance of Fluorine-holding. In contrast to pure LDH products, synthesizing LDH in situ has a more simple process and calls for lower cost, which will benefits its application.