Study On The Treatment Of Fluorine-containing Wastewater By Crystallization Induced TMF Membrane

With the rapid development of industry,the fluorine ore mining and processing,the production of fluorine and its fluoride will produce a large amount of fluorine-containing wastewater,which will bring great harm to the environment and human beings.At present,chemical precipitation is widely used in the treatment of industrial fluorine-containing wastewater,but the presence of high moisture content sludge,unstable operation of the process,the disadvantages of poor settlement.Therefore,this thesis designs crystallization-inducing joint TMF fluoride film process,the TMF membrane system is mainly used for advanced treatment of the secondary chemical coagulation sedimentation section,so that the final effluent[F-]is less than 1 mg/L,and the fluorine removal effect is better.First,based on the CaCl₂-PAC-PAM defluoridation process,a pilot test on fluorine-containing wastewater was carried out,the optimal operating parameters of the process were determined by a single factor test method;Secondly,CaF2 was added as a seed crystal in the chemical precipitation stage,and investigated the influence on removal of sludge sediment and other process parameters before and after contrast segments seeded,the single factor experiment and orthogonal test are used to determine the optimal scheme for the implementation of the process after seeding;In order to make the fluorine removal effect better,the study design CaCl₂-seed-PAC-PAM fluoride membrane combined TMF processes and experimental pilot study,obtain the optimal operating process parameters of the pilot test.The main findings are as follows:?1?The optimum process parameters for the treatment of fluorine-containing wastewater by CaCl₂-PAC-PAM process are:primary chemical coagulation section,Calcium:fluorine molar ratio was 3,the pH was 10,the reaction stirring speed was controlled to 180 r/min,the static settling time was 100 min,and the PAC dosage was 350 mg/L.Under this condition,the fluoride ion concentration of 15 mg/L liter down to 3.2 mg/L,and the pH was 10.Secondary chemical coagulation section,Secondary Calcium:Fluorine molar ratio was 1.7,stirring speed of 160 r/min,allowed to settle time was 35 min,PAC 260mg/L,PAM dosage 3mg/L.After two final treated effluent not reach lmg/L or less standard,the final effluent[F-]was 2.18mg/L,pH value of 8,the sludge moisture content is about 75%higher.?2?The calcium fluoride as a seed crystal and added to the chemical precipitation section,obtained after seeding process by orthogonal optimal reaction conditions:the one chemical coagulation pH control section 9,Calcium:Fluorine molar ratio is 2,seed crystal dosage of 0.2g/L,PAC 300mg/L,a fluorine ion concentration of the effluent was 2.5mg/L,pH 8.5.The secondary chemical coagulation section was added with calcium chloride according to a calcium:fluorine molar ratio of 1.1,the resting time was 70 min,the PAC dosage was 150 mg/L,and the PAM dosage was 4 mg/L.Two residual fluorine concentration of the final effluent 1.12mg/L,pH 7.5.It can be seen that the dosage of the agent is reduced,the moisture content of the sludge is reduced to about 60%,and the effect of removing fluorine is enhanced,but the fluorine concentration does not reach the standard of lmg/L or less.?3?Pilot experiments were carried out on the defluorination process of CaCl₂-seed-PAC-PAM combined with TMF membrane.The process optimum operating parameters are:influent fluoride concentration between 5?15mg/L,pH between 8 and 9,fluoride wastewater was 0.4L/min,calcium chloride tank concentration was 0.870g/L,and reagent addition flow rate was 0.04L/min,the amount of seed 2.7g/L,flow rate 0.04L/min,PAM concentration of agent tank 0.06g/L,adding an agent flow rate of 0.03L/min,the concentration of PAC canister was 3.5g/L,and the flow rate of drug addition was 0.06L/min,the final effluent fluoride ion concentration was below lmg/L,and the pH between 6 and 9,which is up to standard discharge.The results showed that:CaCl₂-seed-PAC-PAM combined with TMF membrane defluorination process can not only stabilize the effluent,but also effectively improve the defluorination efficiency,and has a good application prospect and environmental significance.