Preparation Of Alumina With Different Morphologies And Its Aplication In Defluoridation From Water

The World Health Organization pointed out that when the concentration of fluoride in water exceeds 1.5 mg·L^-1,it will cause harm to human health and cause diseases such as dental fluorosis and skeletal fluorosis.According to statistics,more than 200 million people around the world drink fluoridated water,and more than 70 million people suffer from fluoride-related diseases.Therefore,it is very important to remove excess fluoride ions from drinking water.There are many methods for fluorine removal,of which adsorption is the most cost-effective method.Industrially,activated alumina is often used as an adsorbent for removing fluoride ions in water.Activated alumina is generally prepared by calcining boehmite at high temperature and undergoing topological transformation.Boehmite with different morphologies will have different exposed crystal planes,thus possessing some special chemical properties.However,flake and fibrous alumina will have different stacking methods from spherical alumina,so it is possible to break through the contradiction that traditional alumina cannot have both large specific surface area and large pore diameter.Nano-alumina with specific morphology has gradually become a new favorite in the field of materials due to its unique properties.The controllable preparation of boehmite with specific morphology has very important application value.Based on the previous research results in laboratory,the sodium aluminate-aluminum sulfate neutralization method was used,and the primary particle shape was controllably prepared by adjusting the pH value of the titration end point,the crystallization time,the crystallization temperature and the crystallization method.Boehmite with flake,rhombic flake and fibrous morphology were obtained by calcining it to obtain activated alumina with different morphologies.The adsorption properties of activated alumina with different morphologies for fluoride ions in water were systematically studied,and relationship between alumina adsorbent structure and adsorption performance were explored.The adsorption study results show that,based on the similar specific surface area,activated alumina with different morphologies exhibited different adsorption capacities.The saturated adsorption capacities of spherical,flake,rhombic flake and fibrous alumina were 35.0,87.5,46.5 and 49.0mg·g^-1,respectively.This is attributed to differences in the number of surfactant sites and pore structure.The results of studies shows that the adsorption process of fluoride ions by alumina adsorbents with different morphologies conformed to the pseudo-second-order kinetic model and the Freundlich isotherm adsorption model.In order to reduce the production cost and improve the repeated utilization rate of adsorbents,activated alumina is regenerated,so as to improve the overall efficiency of the activated alumina for defluorination.The adsorbed activated alumina is released by different regeneration methods to release the adsorbed fluoride ions and restore the adsorption capacity.Then,the regeneration process of alumina with different morphologies was studied comprehensively.The regeneration results shows that the morphology and pore structure of alumina adsorbents were affected by regeneration,and the adsorption capacity decreased with the regeneration times.Comparing several alumina adsorbents with different morphologies,the specific surface area and pore structure parameters of fibrous alumina adsorbent are basically unchanged after regeneration,and the morphology is basically unchanged after five times of regeneration,and can still maintain a high adsorption capacity.It shows that the fibrous alumina has strong stability and is suitable for multiple regeneration cycles.