Research On F^- Adsorption By Two Types Of La₂O₂CO₃ Adsorbent

Fluoride is a naturally occurring element in minerals.Fluoride is essential to dental health when ingested at concentrations between 0.7 and 1.0 mg/L. However, water intake with high F- concentrations can cause dental and skeletal fluorosis, increasing susceptibility to renal diseases and cancer, as well as affecting brain development and reduced intellectual coefficient in school-age children. 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"（GB5949-2006） in the specific provision: fluoride content in drinking water standard is not higher than 1.0mg/L Adsorption is the most widely used method to remove Fluoride. It has many advantages such as high efficiency, stable effluent, simple process and convenient operation, economical. Properties of adsorbent is a key factor affecting the adsorption process, economic, efficient agent become the constant pursuit of the goal.Rare earth element widely exists in nature. It has been aroused widely concern due to its excellent biological properties and ion exchange, and excellent adsorption capacity.In order to develop a good adsorbent to remove fluoride, two La₂O₂CO₃ adsorbent in this paper, was used to remove fluoride from groundwater.The as-prepared sample was characterized by X-ray diffraction（XRD）, Fourier transform infrared（FT-IR）, scanning electron microscopy（SEM） and Brunauer-Emmett-Teller（BET） surface area measurement. A series of batch sorption experiments were conducted to study the influence of various factors such as p H,adsorbent dose, initial fluoride concentration,temperature, equilibrium contact time and co-existing anions on the sorption of fluoride. Using batch methods, we studied the adsorption-desorption-regeneration behavior of fluoride onto the adsorbents. According to the FT-IR and SEM analysis, the mechanisms of fluoride removal by the adsorbent and its regenerations were suggested.XRD analysis indicated that the adsorbent was La₂O₂CO₃, FT-IR analysis indicated that the hydroxyl groups on the adsorbent surface were involved in the fluoride adsorption.The fluoride adsorption data on the particle La₂O₂CO₃ adsorbent agreed well withthe Langmuir mode. The saturation adsorption capacity of particle La₂O₂CO₃ adsorbent was 27.63 mg/g. The fluoride adsorption data on the spherical La₂O₂CO₃ adsorbent agreed well with the Freundlich mode. The adsorption process followed the second-order model for fluoride. The qe,cal obtained from second order accord well with the qe,exp from the experiment. The effects of co-existing anions on the sorption of fluoride followed the decreasing order of HCO3- > HPO42- > SO42- > NO3- > Cl-.Experiment data shows that the particle La₂O₂CO₃ adsorbent has a better adsorption effect than the spherical La₂O₂CO₃ adsorbent.The uesd La₂O₂CO₃ adsorbent could be regenerated by sodium hydroxide, when the sodium hydroxide’s concentration is 1.0mol/L, the particle La₂O₂CO₃ adsorbent can be reused in applicability. The water sampling from a village in Hunan containing fluoride, it could be adsorbed effectively by the particle La₂O₂CO₃ adsorbent.