Study On Synthesis And Performance Of Polyacrylate Chelating Polymer Flocculant

Heavy metal ions and its compounds have significant toxicity and are notbiodegradable, they can move into human body through food chain, therefore, thewastewater containing heavy metal ions will do great harm to the environment and thehealth of human beings, so it is very urgent for us to treat polluted water. In existingwater treatment technology, chelated precipitating method is broadly used and provedto be simple, powerful and economical. So the development of effective and powerfulflocculants is becoming more and more important. This paper was based on thatacrylic acid was easily polymerized and dithiocarbamic acid possessed favourablechelating heavy metal ions, a polyacrylate chelating polymer flocculant （PACPF） wasdesigned and synthesized. The properties of PACPF were investigated systematicallyand applied it dealing with the actual electroplating wastewater.Amino ethyl methacrylate （AEMA） was synthesized by using Methylmethacrylate（MMA） and Ethanolamine（EOA） as raw materials through esterexchange reaction; then the homopolymer of AEMA, Polyamino ethylmethacrylate（PAEMA） was synthesized by free-radical polymerization; finally,PACPF was prepared for using PAEMA reacting with NaOH and CS₂by xanthationreaction. The optimum conditions of esterification reaction were as follows:n（MMA）∶n（EOA）=2.0:1, the amount of catalyst （Calcium hydroxide） and inhibitor（Phenothiazine） were1.5g,0.3g, respectively. Reaction time was4h and reactiontemperature was80℃. In the polymerization: m（APS）：m（AEMA）=1∶100, thetime of reaction was4h when temperature was60℃after inputting oxygen to disposeof nitrogen which lasted for30min. The optimum conditions of xanthation were that:n（PAEMA）∶n（NaOH）∶n（CS₂）=1：1.05：1.2, optimum temperature was30℃andoptimum time was4h. The final PACPF was characterized by IR,¹H NMR andelementary analysis.Taking the simulated wastewater as an example, the effect of dosage of PACPF,pH value, stability of precipitates and the leached rate of heavy metal wereinvestigated. The precipitates could be leached by acids to recover the heavy metalions. We found that, among a quite wide pH value, not only PACPF can removed thefree heavy metal ions easily, but also had the same effect on complexing heavy metalions with turbidity, the residual concentrations of heavy metal ions fully reach thefirst grade criteria of China’s Integrated Wastewater Discharge Standard （GB8978-1996）; PACPF had selectivity on different heavy metal ions, the generalselectivity order we found in the experiment was Cu²⁺＞Pb²⁺＞Cd²⁺＞Zn²⁺, and theflocs were so stable that not to produce second pollution in natural environment,furthermore, the heavy metal ions in the flocs could be recovered by leaching throughacids.Taking the actual electroplating wastewater as an example, the concentrations ofCOD, Cu²⁺and Ni²⁺were901.76mg/L,102.08mg/L and55.38mg/L, respectively.The effect of dosage of PACPF, pH value, stability of precipitates and the leached rateof heavy metal ions were investigated. The precipitates could be leached by acids torecover the heavy metal ions. When the actual electroplating wastewater was treatedby PACPF or Al₂（SO₄）₃alone, the results showed that the residual concentrations ofCu²⁺、 Ni²⁺and COD were much higher than Discharge Standard. Using thecombination of PACPF and Al₂（SO₄）₃, the actual electroplating wastewater can betreated effectively and fully met the China’s Emission Standard of Pollutants forElectroplating （GB21900-2008）. In neutral or alkali conditions, when the dosages ofPACPF and Al₂（SO₄）₃were7.5g/L,150mg/L, respectively, the removal rates of Cu²⁺,Ni²⁺and COD were99.52%,99.61%and96.45%, meanwhile, the residualconcentrations were0.49mg/L,0.216mg/L and32.25mg/L, respectively. Compare toPACPF, the combination of PACPF and Al₂（SO₄）₃had well settleability and the flocswere very stable. Cu²⁺and Ni²⁺in the flocs could be recovered by leaching throughacids.In a word, PACPF provided with simple treatment method, high efficiency andgood results. Therefore, it had good society and economy benefit, undoubtedly itwould have favourable application prospect in wastewater treatment.