The sewage which often contains high amount of phosphate can cause seriouspollution, if they do not be disposed and discharged into the environment directly. Thephosphate in water is one of the main factors causing eutrophication. When a certainconcentration of phosphate is reached, eutrophication will occur and damage theecological environment of the water. Therefore, the sewage must be dephosphorizedbefore being discharged into the environment.Fly ash is a waste produced by the energy power plants, and improper disposal couldpollute the environment. Fly ash has a certain adsorption performance because of itsunique physical and chemical properties, and can be used as an adsorbent in thewastewater treatment field. If fly ash is used to deal with the phosphate in the biologicalwastewater directly, the effect is bad. So fly ash must be modified to improve theadsorption performance.This paper adopted wet process modification and chose the four modification agentsuch as hydrochloric acid, sodium hydroxide, aluminum sulfate and ferric chloride tomodify fly ash. Then we found that the phosphorus removal effect of fly ash modifiedby ferric chloride was the best one. The proper operating conditions of phosphorusremoval was determined by the static adsorption experiment: the concentration ofphosphorus in100mL simulation wastewater was30mg/L, the amount of the modifiedfly ash was1g, the room temperature was25℃, the pH of the solution did not need tobe adjusted, the removal rate of phosphorus could reach to99%, the adsorptioncapacity of the modified fly ash could be up to2.97mg/g; In the treatment of functionalwastewater, when the dosing quantity of the modified fly ash was1.5g, the wastewatercould meet emission standard after being processed.To further study the thermodynamics and kinetics of the modification of fly ashwhich was dephosphorized by ferric chloride, we found that phosphorus removalprocess was a spontaneous physical adsorption process and it accorded with fly ashLangmuir isothermal adsorption equation, Lagergren level2adsorption rate equationcould be used to fit the experimental data very well, and the control stage of the adsorption process was the internal diffusion stage of the particle. The spread withinrate constant(kid) was0.7321mg/(g·min-1/2).In order to explore the phosphorus removal mechanism of modifying fly ash, fly ashwas characterized by XRD, BET, SEM, EDS and infrared spectrum. The researchreveals that besides the increased surface area of the modified fly ash, the moreimportant reason is that the surface of fly ash particles adsorbs Fe3+and produces staticadsorption effect with the anion of water, which is the main cause of improving theperformance of fly ash. Through the different testing methods, we can get theconclusion that the phosphorus removal process of fly ash modified by ferric chlorideis a kind of physico chemical adsorption process.The dynamic testing study showed the fly ash packing column, the water intakevelocity, the initial concentration of water and other factors had big influence on thethrough time of beds. |