Study On Pilot Process And Mechanism Of Treating Fluorine-containing Industrial Wastewater By Sludge Recycle Process

The treatment of fluorine-containing industrial wastewater is difficult,and it is often impossible to meet the standard with traditional coagulation and sedimentation processes.In this thesis,based on an in-depth study of the fundamental properties of calcium fluoride particles,comparison of the characteristics of three typical coagulant flocculating characteristics and effluent effect,the introduction of a new sludge return process for the treatment of fluoride-containing wastewater,and determine the pilot operation The best control conditions for the best results.The study on the properties of calcium fluoride particles shows that the theoretical solubility of calcium fluoride is 8.17 mg/L,which is close to the allowable emission standard.When the pH is greater than 5,it can completely react.Increasing the calcium ion dosage can effectively reduce the calcium fluoride solubility.However,increasing the solution ion concentration increases the calcium fluoride solubility.Calcium fluoride colloidal particles are positively charged in water,and their zeta potential pH increases and decreases.The particle size belongs to the scope of colloidal particles,the natural sedimentation rate is slow,and it is necessary to add auxiliary coagulant to settle.The results of the traditional coagulation sedimentation process showed that under the optimal conditions,the effect of effluent between FeCl₃ and PAC was similar,the remaining fluoride ions could be reduced to 10.5g/L,PFS could be reduced to 12mg/L,and the flocculation characteristics were compared.Strength and recovery after crushing.show that,Too low and too high pH value and dosing amount were unfavorable to floc formation.PAC controlled pH=8.5,dosage 50mg/L,PFS controlled pH=8,dosage 50mg/L,FeCl₃ controlled pH=7,Dosage 50mg/L,the flocculation speed was the fastest,the floc size was the largest,and the size of FeCl₃flocs was 1.5 times as large as that of PFS and PAC and the floc formation speed was faster,the optimal alkalinity was lower.Dosing rate was an important factor affecting the floc strength and recovery performance.With the increased of dosage,the floc strength of FeCl₃,PFS,PAC floc increased to 50%,60%,70%respectively,but the recovery performance decreased,which can be reduced from 120%to less than 20%.Under the same conditions,the recovery factor of FeCl₃ was 0.5 times that of PFS and PAC.Sludge reflow process for the treatment of fluorine-contained industrial wastewater:Pilot tests show that pH₁=11,pH₂=8.5,PAC dosing volume 50 mg/L,PAM dosing volume 3 mg/L,sludge return ratio 40%under actual operation The floe size formed by the process is the largest,and the best effluent effect is achieved.The fluoride ion in the effluent can be reduced to 6.37 mg/L.The mechanism of the sludge reflow process is elaborated:the return sludge can enhance the contact flocculation effect and its surface is formed."Pectin"has a strong adsorption effect,return sludge equivalent to increase the amount of Ca?OH?₂ dosing,in which calcium fluoride crystal nuclei can promote the formation of calcium fluoride.