The Synthesis,Structure Characterization And Properties Of Polymer Decolorizing Flocculants Made FromDicyandiamide And Formaldehyde

Wastewater containing water-soluble dyes is one of sewages that are most difficult to be treated. Conventional flocculants widely used in the treatment of wastewater containing suspended dyes usually yield poor decoloration rate in the treatment of wastewater containing dissolved dyes. The cationic condensation polymer of dicyanodiamide(DCD) and formaldehyde(HCHO) showed special performance in the decolorization of wastewater containing dissolved dyes. On the basis of the investigation of factors affecting the polymerization of DCD-HCHO and properties of DCD-HCHO polymers, a highly efficient decolorizing flocculant nominated DFA is synthesized using AlCl3·6H2O as catalyst and NH4Cl as modifier. The molecular structure of DFA is characterized by IR, 1HNMR and 13CNMR. Its electric charge density and intrinsic viscosity are measured. The interaction between active red X-3B and DFA is studied thermodynamically with the method of equilibrium dialysis. Factors affecting the flocculation of dye solution, such as shaking style, temperature, pH and dye concentration of the solution, electric charge density and intrinsic viscosity of flocculants, are discussed. The qualitative relationship between the structures of various dyes and their decoloration efficiency is analyzed. DFA shows a high performance in decolorizing solutions of active dye, acidic dye and direct dye as well as suspension of vat dye and disperse dye. Preliminary tests show DFA a potential decolorizing flocculant in the dispose of wastewater from printing and dyeing plants. The following conclusions can be drawn from the research:(1) DFA, a DCD-HCHO polymer synthesized using AlCl3.6H2O as catalyst and NH4Cl as modifier, is a highly efficient cationic decolorizing flocculant. Its electric charge density and intrinsic viscosity are higher than the corresponding polymer prepared in the absence of AlCl3·6H2O.(2)Characterization of DFA by IR, 1HNMR and 13CNMR shows it possesses several active groups that can react with dyes in one or another way to perform decolorization. Some possible chain segment structures are listed below:(3) Study of the structure-property relationship of DFA manifest that electric charge density and intrinsic viscosity are directly related to decolorizing efficiency. Decolorizing efficiency is improved with the increase of electric charge density and intrinsic viscosity of flocculants.(4) Thermodynamical study of the interaction between active red X-3B and DFA shows that the binding constant K1 varies with temperature and getsits summit on a temperature of 303K(30℃). The result suggests that the mechanism of decolorizing flocculation of dye solution with DFA is a multiple function of electric neutralization, absorptive bridging and interaction between flocculant and solvent.(5) Study of factors affecting the flocculation of dye solution gives the optimized conditions of decolorizing operation: DFA concentration:300-600mg/L;pH:4-10;temperature:20-30℃.(6)The decolorizing performance of DFA for solutions of active dye, acid dye ,direct dye and suspension of vat dye and disperse dye as well as wastewater from printing and dyeing plant is compared with that of polyacrylamide(PAM),polyacrylnitrile-dicyanodiamide ,polymer(PAN-DCD), DC-491(a commercially available DCD-HCHO polymer flocculant) and several other flocculants. The decolorizing performance of DFA is superior to that of PAM,PAN-DCD,DC-491,etc.