Study On Preparation Of Ligand Exchange Flocculant And Its Performance Of Defluoridation

Drinking water safety is concerned in today's world. With industrial development, population expansion, source of drinking water are subject to different degrees of pollution. Worldwide shortage of water resources, deterioration of water environment and drinking water supply emergencies constitute the three major problems, which seriously threat to the safety of drinking water. Underground water quality in China is not optimistic. In many provinces (autonomous regions and municipalities), there are different endemics because of drinking the water which is not up to national standard, in which the most common is fluorosis disease due to drinking high fluoride water. Light sufferers were expressed as dental fluorosis, severe sufferers were expressed as skeletal fluorosis which can develop severe disease and even cause permanent disability, loss of working capacity. The current methods of defluoridation at home and abroad have advantages and disadvantages, and the disadvantages of method lead to it not conducive in remote rural and underdeveloped areas. So it is significant and necessary to research an efficient, safe, low-power fluoride materials to solve this social problem.This paper presents new idea and method of fluoride removal which is based on the Mannich reaction principle to synthesize graft flocculant, in which polyacrylamide (PAM) is as the main chain backbone, grafted with iminodiacetic acid (IDE) and diethylenetriamine (DETA). So the main chain of polyacrylamide can receive chelating groups. According to hard and soft acid-base theory, synthetic graft flocculant can chelated Fe3+/A13+ to synthesize ligand exchange flocculant. Because F"and Fe3+/A13+ can form stable complexes, with synthetic ligand exchange flocculant as the fluoride materials, through ligand exchange, we can achieve the purpose of reducing the fluoride concentration in water.Studies have shown that polyacrylamide can be grafted with IDE, DETA.Through flocculation experiments, we know the synthetic flocculant still has flocculation performance. Many factors like pH, material ratio, reaction temperature, reaction time, stirring rate were be considered in the research, and the author obtained graft flocculant which iminodiacetic acid in the grafting yield 36.9%, flocculation capacity expressed as the rate of turbidity up to 92.1%; the amination degree of DETA can reach 33.3%, the rate of turbidity is 91.2%. Next experiment shows that graft flocculant can chelated Fe+, Al3+, in certain pH, initial concentration,temperature and reaction time, iminodiacetic acid grafted PAM prepared ligand exchange flocculant can chelated 2.91mg Fe3+, the capacity of chelating Al3+ is 1.84mg/mL; DETA grafted PAM chelating Fe3+ content is 2.98mg/mL, Al3+ chelating capacity is 2.13mg/mL; Following research of defluoridation proved that ligand exchange flocculant can remove fluoride, and in the synthetic flocculant, fluoride removal capacity of the flocculant grafted with DETA chelating Al3+ is best, fluoride removal rate of 67.8%. By changing the way and adding a second deflocculation experiments can be further improved fluoride removal efficiency, in which the initial F- concentration of 4.88.0mg/L reduced to 1.20 mg/ L, fluoride removal rate of 76%.Acording the new idea and method of defluoridation and after a large number of experimental studies, ultimately, the author obtained a new type of fluoride reagents, which have good fluoride removal capacity of fluoride, and low energy consumption, simple operation. This new method fluoride offers the new idea and direction for researching defluoridation.