Study On The Preparation And Mechanism Of Sodium Alginate Entrapped Sludge Gel Beads For Fluoride Removal

Coagulation process is a basic pretreatment method of water purification widely used in water supply plants.Aluminum salt coagulant is widely used in water supply treatment process because of its effectiveness and low cost.The by-product of water treatment is feedwater aluminum sludge.In recent years,people’s requirements for drinking water quality have gradually increased.In order to meet the increasing demand,the construction scale of water treatment plant has been gradually expanded,resulting in a sharp rise in the discharge of water supply sludge.The annual output of water supply sludge is huge,but the cost of sludge landfill disposal is high,and most countries prohibit discharge to water bodies.Therefore,more appropriate disposal methods must be found.The resource utilization of sludge can not only solve the negative impact of sludge on the environment and reduce the economic burden of water plants and related industries,but also provide new ideas for the application research of sludge in other fields.In order to achieve the goal of sludge recycling,a new type of adsorption material,SAS Sodium alginate entrapped sludge gel beads,was developed in this study.In order to achieve the purpose of fluoride removal,the specific research contents are as follows:Preparation of sludge gel beads:first,the sludge from the south north water treatment plant was selected and then modified by three ways of acetic acid,aluminum sulfate solution and high temperature calcination to further improve the adsorption performance.The results showed that the best modification conditions were to calcinate 4h at 400℃.Due to the strong dispersion of sludge powder in water and difficult to recover,this study takes sludge granulation as the research goal and sodium alginate as the embedding agent.The optimal preparation scheme is determined through orthogonal test,that is,the embedding amount of sludge is 12g/100m L,the concentration of sodium alginate is 1wt%,and the concentration of calcium chloride is 2wt%.The surface of the prepared gel beads is rough and there are honeycomb pore structures with different sizes.The N₂ adsorption desorption curve shows that the material is mesoporous material.The influencing factors of adsorption and regeneration experiments:the influence of sludge gel ball dosage,adsorption time,temperature,p H and coexisting ions on the performance of fluoride removal were investigated by using the control variable method.The best dosage of sludge gel ball was 8g/L,and the adsorption process showed a"fast adsorption and slow equilibrium"adsorption trend.The temperature control was best at20℃,and the adsorption capacity decreased with the increase of p H.It shows good adsorption performance in the range of 6～8.The influence of coexisting ions on the properties of gel spheres is NO₃^-<Cl^-<SO₄^2-<PO₄^3-.The regeneration test was carried out with Na OH,Na Cl,Na NO₃ and HCl respectively,and the regeneration effect of the above regeneration solution was not ideal.Research on adsorption mechanism and application performance:according to the analysis of adsorption kinetics,the fitting coefficient of quasi second-order kinetics is the highest,indicating that the adsorption process is mainly chemical adsorption.The study of adsorption isotherm shows that Freundlich adsorption isotherm model can better describe the adsorption process,indicating that the adsorption process belongs to multi-molecular layer adsorption.Thermodynamic studies show that the adsorption process is a spontaneous exothermic reaction,and the decrease of temperature is conducive to the adsorption reaction.Combined with the analysis of the morphology,elements and functional groups of the gel beads before and after adsorption,the adsorption mechanism includes physical adsorption,ion exchange and electrostatic attraction.The concentration of residual heavy metal ions after sludge gel ball adsorption is in line with the safe concentration limit.The mass loss rate before and after the gel ball adsorption is 3.75%,and the mechanical strength is better.Compared with the other two kinds of fluoride removal adsorbent in the research group,the application cost is the lowest.Therefore,the sludge gel ball has certain practicability and economy.In conclusion,using aluminum sludge as raw material and sodium alginate as embedding agent,fluoride removal materials with good adsorption performance can be prepared,which can not only realize the resource utilization of sludge and reduce the economic burden of sludge disposal in water plants,but also provide new ideas for the research of fluoride removal adsorbents.