| With the speeding up of the urbanization and industrialization, the water shortagesbecome an increasingly outstanding problem and the water pollution becomes one of themajor issues which mankind is facing in the21st century. To solve these problems,wastewater treatment is an effective way. The wastewater which has high turbidity and darkcolor is a kind of pollution which can be hardly deal with. So synthesizing the cationicpolyacrylamide flocculants with good flocculating performance and multi-functions has greattheoretical significance and application value in the treatment for high turbidity and dark colorwastewater. In this paper, the cationic polyacrylamide flocculants were synthesized byaqueous solution copolymerization using acrylamide(AM) and methacryloxyethyltrimethylammonium chloride(DMC) as monomers and ammonium persulphate as initiator. Based onsimilar compatibility principle, the product (white amorphous solid cationic polyacrylamide)was separated from the reaction system by reducing the polarity of the solvent. In this paper,the molecular weight and cationic degree were used to characterize the synthesized productand synthesis reaction. In order to evaluate the activity of AM and DMC, the reactivity ratiosof the cationic copolymer were determined. In this paper, the self-made P(AM-DMC) wasalso used for the study on the flocculating performance to prove that it has good practicalapplication performance in the wastewater treatment.The synthesis of single-factor experiments investigated the impact of pH value,theamount of initiator, reaction time, total monomer and mass ratio monomer on the relativemolecular mass and cationic degree. Through the orthogonal experiments, the optimizedsynthesis conditions of the polymerization are determined. The optimum conditions ofpolymerization are obtained as follows: the pH value is6, the amount of initiator is1.5ml(5g/L), the reaction time is40min and the total monomer is8%(m(DMC):m(AM)=1:3).Under these conditions, the P(AM-DMC) with1.72×106g/mol molecular weight and14.32%cationic degree was synthesized.The reactivity ratios of the cationic copolymer were obtained by the Fineman-Rossmethod, Kelen–Tudos method and Yezrielev-Brokhina–Roski method, respectively. Theresults show that the values of the reactivity tatios determined by K-T method and YBRmethod are more accurate. The reactivity ratios of DMC and AM are rDMC=0.595rAM=3.737calculated by K-T method and YBR method. The F-f graph shows that the type ofcopolymerization reaction is no constant ratio point copolymer.The self-made P(AM-DMC) under the optimized synthesis conditions was used for the study on the flocculating performance. The evaluation index was the turbidity removal rate ofbentonite solution and the color removal rate of Methylene blue solution. Through thesingle-factor experiments and the orthogonal experiments, the optimized conditions offlocculation are determined. For bentonite solution, the optimized conditions of the turbidityremoval rate are obtained as follows: the amount of flocculants is1.0ml(0.05%), the pH valueis4, the stirring rate is100r/min and the standing time is10min. The turbidity removal rate ofbentonite solution can reach66.12%. For Methylene blue solution, the optimized conditionsof the color removal rate are obtained as follows: the amount of flocculants is0.8ml(0.05%),the pH value is8,the stirring rate is100r/min, the amount of bentonite is100mg/L and thestanding time is10min. The color removal rate of Methylene blue solution can reach94.58%.Under these optimized conditions, the turbidity removal rate and the color removal rate for thepapermaking wastewater which was collected from Ningxia province can reach79.99%and88.25%. The residual rate of flocculants in water is9.41%. From the above data, theself-made P(AM-DMC) can meet the basic needs of practical application and its advantage issmall amount, good effect, and less residual in water. |
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