Study On The Combined Treatment Of Fluorine-Containing Wastewater By Precipitation And Adsorption

With the rapid development of China’s nuclear industry,a large amount of fluorinecontaining wastewater is generated in the process of uranium conversion.Untreated or substandard treated fluorine-containing wastewater is discharged into the environment,which poses a serious hazard to human health and causes great pollution to the natural environment.In this paper,fluorinated wastewater is treated by precipitation and adsorption methods.This paper first treated the simulated fluorinated wastewater(containing 7000 mg·L-1 fluoride)by precipitation method.In the precipitation defluoridation stage,calcium hydroxide was used as precipitant,polymeric aluminum chloride(PAC)as a coagulant,and polyacrylamide(PAM)as a coagulant,and experiments were conducted to make the fluoride ion concentration lower than 10 mg·L-1 and determine the optimal defluoridation parameters.After that,deep fluoride removal was carried out,and the adsorbent FTBCC-Mg/La(C)was prepared by loading bimetallic(Mg/La)on French plane tree ball crude cellulose(FTBCC)using co-precipitation method,and FTBC-Mg/La(U)was prepared by reacting French plane tree ball cellulose(FTBC)with bimetallic(Mg/La)using the ultrasound-assisted method,and the preparation conditions of both materials were optimized,We also optimized the preparation conditions,characterized and investigated the fluoride removal performance of the two materials,and applied the deep fluoride removal to the two materials,and finally compared the materials and the fluoride removal effect.The main results are as follows:1.The best process of fluoride removal by precipitation is as follows:for the simulated fluorine wastewater of 7000 mg·L-1,the optimal calcium-fluoride ratio(Molar ratio)is 1,the reaction time is 40 min,the reaction pH is 6,the settling time is 120 min,and the effluent fluoride ion concentration is 19.23 mg·L-1 at room temperature with PAC as a coagulant and PAM aa s coagulant.The reaction time is 30 minutes,the reaction pH is 7,the settling time is 90 minutes,and the fluorine ion concentration is 7.82 mg·L-1.After several experiments,the fluorine ion concentration of the effluent is stabilized below 10 mg·L-1,which meets the national emission standard.2.FTBCC-Mg/La(C)composite material was prepared by co-precipitation method,the best preparation conditions:the molar ratio of magnesium salt and lanthanum salt was 1:1,the total concentration of magnesium ion and lanthanum ion was 1 mol·L-1,the reaction pH was 10,and the roasting temperature was 500℃.In treating the simulated fluorinated wastewater of 10 mg·L-1,the optimal treatment conditions were:the optimal dosage of FTBCC-Mg/La(C)composites was 3.0 g·L-1,the optimal reaction pH was 3,and the optimal adsorption time was 3 h.After the treatment,the fluoride ion concentration in the wastewater was reduced to 0.633 mg·L-1.The FTBCC-Mg/La(C)composites showed The maximum adsorption amount(qmax)of FTBCC-Mg/La(C)composites at 298 K and 308 K were 9.76 mg·g-1 and 10.98 mg·g-1,respectively,and the adsorption process was a heat absorption process.the Langmuir model(R2=0.9992-0.9994)could better describe the adsorption process.the fluoride removal process of FTBCC-Mg/La(C)composites was more consistent with the pseudo-secondary kinetic model.Ultimately,FTBCC-Mg/La(C)depth fluoride removal was better,and the effluent stability was less than 1 mg·L-1 after several verifications.3.FTBC-Mg/La(U)composites were prepared using ultrasound-assisted method.The best preparation conditions:the molar ratio of magnesium salt and lanthanum salt is 1:1,the total concentration of magnesium ion and lanthanum ion is set to 0.9 mol·L-1,and the best preparation ultrasonic time is 20 min.When treating the wastewater with fluoride ion concentration of 10 mg·L-1,the best treatment conditions are:the best dosage of FTBCMg/La(U)composite is 0.9 g·L-1,the best reaction pH The maximum adsorption amount(qmax)of FTBC-Mg/La(U)composites at 298 K,308 K and 318 K were 28.19 mg·g-1,30.41 mg·g-1 and 32.40 mg·g-1,respectively.The Langmuir model(R2=0.9988-0.9995)could better describe the adsorption process.The fluoride removal process of FTBC-Mg/La(U)composites was more consistent with the pseudo-secondary kinetic model.Finally,FTBCCMg/La(C)is more effective in deep fluoride removal,and the effluent is stable after several verifications for deep fluoride removal from fluoridated wastewater.According to the above results,both adsorbents can be used for deep treatment of fluoridated wastewater.However,compared with FTBCC-Mg/La(C),the adsorption performance of FTBC-Mg/La(U)material is more excellent and the use environment is neutral,which shows a wide application prospect in the treatment of fluoride-containing wastewater.