Study On Preparation Of Macromolecule Heavy Metal Flocculant MAPEI And Its Performance

As the fresh water resource reduce increasingly and all over the world attach importance to environmental protection gradually, people give more and more notice to the development of the water treatment flocculants. Flocculants can increase solid/liquid desperation efficiency, and have been applied to many industry regions. Cationic polymeric flocculants which can dissolve in water very well are a kind of efficacious medicaments, and have good application in water treatment, paper manufacture, smelt mineral and so on. Therefore, to look for efficiently and multi-function polymeric cationic flocculants is one of the the point research contents of the environmental science and the engineering realm nowadays.Flocculation is one of the most important methods for water treatment. But the main objecs of flocculation only are the hydrophobic colloids and suspended particles, not soluble species. Industrial wastewater containing heavy metal ions contaminates biotic environment greatly, such as chromium, copper, nickel, mercury and so on. Because heavy metal ions have a low-grade biodegradability, play along with food chain and beaccumulated in living body at last, destruct living body's normal metabolism. Now the treatment of wastewater containing heavy metal ions has been paid great attention.In this thesis, a new tape of novel water-soluble macromolecule heavy metal flocculant mercaptoacetyl polyethyleneimine(MAPEI)was synthesized by reacting polyethyleneimine with mercaptoacetic acid. MAPEI not only removes turbidity-causing substance by flocculation,but also soluble heavey metal species by chelation efficiently. Treatment of waste water containing heavy metal ions with MAPEI can chelate with Cu²⁺,Ni²⁺,Hg²⁺,Pb²⁺ under room temperature, the chelation is firm, so MAPEI can remove both soluble heavey metal species and insoluble substances, reduce subsequent equipments and make disposal heavy metal wastewater easier.The reseach of MAPEI contains two parts, preparation of macromolecule heavy metal flocculant and its performance. The frist part is to reseach some factors which effect the synthesis experiments, such as concentration of reactant, proportionality of reactant, reacing time, the sequence of reactant, the dosage of catalyzator and so on. Based on the experiments results the optimum synthetic condition has been defined, as follows: under room temperature, concentration of polyethyleneimine is 4%, the mole ratio of PEI and TGA is 1 : 2, reacting time 12 hour, the sequence of reactant(more important factor)is PEI,catalyzator and TGA, the catalyzator ,of amidation reaction is carbodiimide hydrochloride(EDC), the dosage of EDC is Imol·L^-1 6ml. The final synthesized MAPEI by optimurn synthetic condition is evaluated by using infrared optical spectrum analysis and elemental analysis, it contains 4.598% sulphur.The second part of this experiments is to study on MAPEI's performance by using the target water sample with tap water or electroplating wastewater individually, main factors which affect the removal rates of heavy metal and turbidity and its mechanism. For example, the effect of dosage of MAPEI, pH value, heavy metal and turbidity-causing substance coexited, settling time, stability of precipitates or MAPEI, the leached rate of heavy metal and so on. The experiments results shows that(such as Cu²⁺): (1)MAPEI has strong binding effect with Cu²⁺, the removal rate of Cu2 reached above 95%; (2)The pH value has a little effect on the removal of Cu²⁺ or turbidity in the pH rage 2～5, lower pH value ofwasrewater is more suitable for the removal of turbidity, but higher pH value is more suitable for the removal of Cu²⁺: (3)When Cu²⁺ and turbidity-causing substance coexist in water sample, Cu²⁺ and turbidity-causing substance promote the removal of each other, and the residual concentration of Cu²⁺and turbidity decrease further: (4)The existence of Na⁺,Mg²⁺,Ca²⁺ in wastewater can promote the removal of Cu²⁺, and make the optimum dosage rage of MAPEI become wider. When Fe³⁺ ions coexist in wastewater, the removal rate of Cu²⁺ will decrease evidently if the MAPEI is not enough in pH3, but it will promote the removal of Cu²⁺ in pH5; (5)The dimension of chelate is more dense, and the sediment is less; (6)The precipitates containing heavy metasl is stable, could be leached by hydrochloric acid to recover the heavy metal, the leached rate could reach 80%; (7)MAPEI is easily oxidized under room temperature.