Preparation Of Magnetic Anion Block Coagulant TAPAM-PDA-Fe₃O₄ And Its Coagulation Performance Study

In recent years,China is strictly monitoring and controlling the discharge of wastewater,and water pollution treatment is the top priority.However,with the continuous development of economy,the amount of wastewater produced is increasing and complicated,so it is urgent to study the treatment of wastewater.Coagulation is a common and very important treatment method in wastewater treatment,in which the key factor is the coagulant which can significantly affect the coagulation effect.Therefore,the research on new coagulants is of great significance.Polyacrylamide（AMPM）is an organic macromolecule coagulant widely used in wastewater treatment.It has strong electronegativity,with good coagulation effect,and can remove positively charged organic/inorganic pollutants by means of electro-neutralization,adsorption bridge,etc.In this paper,using PDAC as the cationic template and 2-acrylamide-2-methyl-1-propane sulfonic acid（AMPS）as the anionic monomer with high grafting efficiency and heat resistance,the template polymerization reaction with acrylamide（AM）was carried out under the irradiation of ultraviolet light,and the anionic polyacrylamide coagulant（TAPAM）with anionic block structure was prepared.Then,PDA and magnetic Fe₃O₄nanoparticles were simultaneously grafted onto TAPAM to prepare the final novel magnetic anion block coagulant（TAPAM-PDA-Fe₃O₄）.Two kinds of coagulants,PDA and APAM-Fe₃O₄,were used as the control group.The three kinds of coagulants were applied to the treatment of methylene blue dye wastewater,crystal violet dye wastewater and nickel（Ni（II））wastewater.The coagulation effect of TAPAM-PDA-Fe₃O₄ was studied.The main research work and conclusions of this paper are as follows:（1）Preparation of TAPAM-PDA-Fe₃O₄.In order to optimize the polymerization conditions,the effects of pH value,n（PDAC）:n（AMPS）,n（AMPS）:n（AM）,n（AM）:n（DA）,n（DA）:n（Fe₃O₄）on the intrinsic viscosity and conversion of TAPAM-PDA-Fe₃O₄ were investigated by single factor experiments.Moreover,response surface analysis was used to explore the influence of six factors on the intrinsic viscosity of the polymerization product TAPAM-PDA-Fe₃O₄ through the design of six factors and three levels,so as to obtain the optimized preparation conditions:When pH value was 8.5,n（PDAC）:n（AMPS）was 0.2,n（AMPS）:n（AM）was 1.0,n（AM）:n（DA）was 1.2,n（DA）:n（Fe₃O₄）was 2.8,and reaction time was 95.0 min,the intrinsic viscosity of TAPAM-PDA-Fe₃O₄ reached1758.445m L/g.（2）Characterization of TAPAM-PDA-Fe₃O₄,APAM-Fe₃O₄ and PDA.Fourier transform infrared spectroscopy（FTIR）showed the characteristic peaks of AM,AMPS and PDA,indicating successful polymerization and grafting.X-ray photoelectron spectroscopy（XPS）analysis showed that Fe₃O₄ particles and PDA were grafted successfully,which showed that Fe₃O₄ particles and PDA were grafted successfully.Thermogravimetric/differential thermal analysis（TGA/DSC）results show that the thermal stability is strong in the range of 27.7～109.7℃.The characteristic peak of Fe₃O₄in X-ray fluorescence diffraction（XRD）and the saturation magnetization of 50.6 Emu/g indicated that the grafting of Fe₃O₄ particles was successful.Scanning electron microscopy（SEM）showed that the specific surface area of the polymeric product was the largest and the densest,indicating that its structure was more conducive to good coagulation effect.（3）The treatment of simulated methylene blue dye,simulated crystal violet dye and simulated Ni（II）wastewater was studied.At the same time,taking the target pollutants as the treatment object and the concentration removal rate of the target pollutants as the index,the coagulation experiments were carried out by comparing the two coagulants TAPAM-PDA-Fe₃O₄ with PDA and APAM-Fe₃O₄.The effects of pH value,initial concentration,dosage and stirring speed on the removal rate of target pollutants were discussed.The reaction mechanism of TAPAM-PDA-Fe₃O₄ was studied by zeta potential for simulated methylene blue dye and simulated Ni（II）wastewater.At the same time,it is found that TAPAM-PDA-Fe₃O₄ not only has the best coagulation effect,but also can adapt to a wide range of pH,with less dosage and cost saving.The experimental results show that:Under the conditions of pH 9,initial concentration of methylene blue 4mg/L,dosage of TAPAM-PDA-Fe₃O₄ 200mg/L and stirring speed 200rad/min,the removal rate of methylene blue by TAPAM-PDA-Fe₃O₄was the highest,which was 97.5%.At the same time,TAPAM-PDA-Fe₃O₄ can achieve stable coagulation effect with high removal rate in the pH range of 5～9,and the removal rate is higher than that of PDA and APAM-Fe₃O₄.Under the conditions of pH 9,initial concentration of crystal violet 50mg/L,dosage of TAPAM-PDA-Fe₃O₄ 300mg/L and stirring speed 200rad/min,the maximum removal rate of crystal violet dye by TAPAM-PDA-Fe₃O₄ is 99.8%,which can be completely removed.And TAPAM-PDA-Fe₃O₄ can achieve high coagulation effect at pH 4～9,which is better than the other two coagulants.Under the conditions of pH value of 8,initial concentration of Ni（II）wastewater of20mg/L,dosage of TAPAM-PDA-Fe₃O₄ of 8mg/L and stirring speed of 160rad/min,the removal rate of Ni（II）wastewater is the best,reaching 99.8%.The pH range is 4～8.