Synthesis And Properties Of Decolorizing Agent Of DCD-FA And EPI-DMA

Dicyandiamide-formaldehyde(DCD-FA)decolorant can be used as one of the effective products that are used in flocculation sedimentation to treat printing and dyeing wastewater.However,the settling effect is not optimized due to the low molecular weight of the condensation polymer formed by dicyandiamide and formaldehyde and the small flocs obtained by the interaction between dye molecules.Therefore,to improve the decolorizing performance of DCD-FA decolorant,a modified DCD-FA flocculant is synthesized with hexamethylenetetramine as modifier and used in the simulated textile wastewater treatment experiment to study its flocculation ability.First of all,single factor experiments were performed to determine the possible effects of molar ratio of reaction materials,reaction temperature and reaction time on the decolorizing performance of the modified decolorant flocculant.The results indicated that the best molar ratio of each material as follows: dicyandiamide: formaldehyde: ammonium chloride:hexamethylenetetramine=1:3.2:0.76:0.02.It is also discovered that the optimum reaction temperature is 85? and the optimum reaction time is 3.5 h.In the case of the same dosage and the same settling time,the modified decolorant outperformed the unmodified decolorant greatly.The unmodified decolorant has a decolorization rate of 89.3% with small flocs and slow settling speed,whereas the modified decolorant has a decolorization rate as high as 98.2% with thick and dense flocs and fast settling speed.Researchs and discussions also took place to determine the possible effects that a series of flocculating conditions may have on the decolorizing performance of this product.These conditions include stirring conditions,flocculation temperature,concentration of dye wastewater,dosage of decolorant,p H value and inorganic salts.The results shown that thedecolorizing performance of the product was optimized by suitable stirring rate and stirring conditions.When a dosage of 100 mg/L is used under the best flocculation temperature,which is 30?,the decolorization rate could reach 98.2%.Furthermore,the relationship between the concentration of dye wastewater and the amount of decolorant has certain practical significance in the treatment of printing and dyeing wastewater.The applicable conditions of the product are acidic and neutral,and it is best suitable for p H=4.It is also found that the salt resistance of the modified decolorant is better than that of the unmodified decolorant.Epichlorohydrin-dimethylamine(EPI-DMA)decolorant that is a cationic flocculant has high cationic degree but low molecular weight.Both of which are very important for its decolorizating performance.In order to improve the situation and increase both the molecular weight and molecular chain of the polymer,EPI-DMA modified decolorizing flocculant was synthesized by using diethylenetriamine as cross-linking agent and flocculation experiments in the simulated dye wastewater were conducted.Similarly,single factor experiments were used to determine the optimum molar ratio of epichlorohydrin to diethylenetriamine and the finding is as follows:epichlorohydrin: dimethylamine: diethylenetriamine=1:0.95:0.05,the optimum reaction temperature is 95? and the polymerization time is 5?6 h.In the case of the same dosage and the same settling time,the modified flocculant had a better performance than the unmodified flocculant.The decolorization rate of the unmodified decolorant is 46.4% with small flocs and the slow settling speed.On the contrary,the decolorization rate of the modified decolorant is 82.3% with thick and dense flocs and fast settling speed.The effects of stirring conditions,flocculation temperature,concentration of dye wastewater,dosage of decolorant,p H value,mixed usage with four kinds of polyacrylamide(PAM),and inorganic salts on the decolorizing performance of the product were discussed.The findings remain as the decolorizing performance of the product is optimized by suitable stirring rateand stirring conditions.The best flocculation temperature is 20?.When a dosage of decolorant is given as 125 mg/L,the decolorization rate could reach82.3%.Mixed usage with four kinds of PAM: amphiphilic,anionic,cationic and nonionic improved the decolorization rate.The each PAM concentration is 2.5 mg/L,the mass ratio of modified flocculant to PAM is 9:1 and the total dosage is 125 mg/L.The anionic PAM is found to be the best with a decolorization rate reaching 85.2%.The applicable condition of the product is acidic.A decolorization rate of 91% was obtained in its best suitable environment of p H=4.The modified decolorant has better salt tolerance than the unmodified decolorant,while the modified decolorant combined with anionic PAM has even better salt tolerance than both.