One-step Synthesis Of Cotton-like Ca-Al-La Composite As Highly Efficient Adsorbent For Fluoride Removal

Fluoride is a naturally occurring element in minerals. Drinking water is the primary source of fluoride intake for human beings. Although fluorine is an essential constituent for both humans and animals in low concentration, dental or skeletal fluorosis could be induced by long-term ingestion of high-concentration fluoride in drinking water. According to the World Health Organization (WHO) guidelines, the upper limit of fluoride concentration in drinking water is1.5mg/L. In the "drinking water health standards"(GB5949-2006) in the specific provision:fluoride content in drinking water standard is not higher than1.0mg/L. Adsorption has been found to be superior to other techniques for fluoride removal based on initial cost, flexibility, simplicity of design, ease of operation and maintenance. The applicability of adsorbent is the key to adsorption. The natural material as bauxite、serpentine、zeolite and bentonite is economic, but adsorption capacity is not good and the operation is the complex. Some the absorbent of rare earth is in high efficiency, but the use of single rare earth element is high cost, not suitable for mass production. To develop and investigate a no secondary pollution and feasible fluoride adsorbent has important scientific and practical significance.Ca-Al-La composite was successfully synthesized as an adsorbent for fluoride removal by an easy one-step hydrothermal process. The as-prepared samples were characterized by XRD, SEM, FTIR, BET and XPS. Batch sorption experiments were conducted to study the influence of various factors such as pH, initial fluoride concentration, equilibrium contact time, co-existing anions on the sorption of fluoride and experiments of natural settlement. The fluoride adsorption by the Ca-Al-La composite agreed well with the Langmuir model. The maximum adsorption capacity of the adsorbent is26.17mg/g. The fluoride adsorption kinetics over the adsorbents was well described by the pseudo-second-order kinetic model. The effects of co-existing anions on the sorption of fluoride followed the decreasing order of PO43->HCO3-> SO42-> NO3-> Cl-. In addition, the removal ability fluctuated slightly over the pH range of2-11, which means that this composite can adapt to a wide range of pH for fluoride adsorption. Besides high adsorption capacity, surprisingly, it is not only cotton-like morphology but also uniform and rules.