Study On Preparation Of Chelating Flocculant And Its Performance Of Removing Cd²⁺, Hg²⁺and Pb²⁺from Wastewater

With economic development, social progress,population growth, drinking water safetyhas become an issual of universal concern in today’s world. Worldwide water shortages, waterpollution and deterioration of water environment, seriously affect the safety of drinking water.The water pollution of heavy metal ions is a typical representative. The Minamata diseasecaused by mercury pollution and the Itai-itai disease caused by cadmium pollution in Japan,the excessive blood lead of children in Fengxiang in Shannxi and Wugang in Hunan show theseriousness of water pollution caused by Cadmium, Mercury and Lead.Solve the waterpollution of heavy metal ion scientific and effectively has become a very importantproblem.The methods to remove heavy metal pollution has both advantages anddisadvantages, is not suitable for the underdeveloped areas.It is very necessary to serch asolution of efficient, security, low-cost and low-power to solve the water pollution of heavymetalion.According to hard and soft acid-base theory, diethylenetriamine（DETA） andtriethylenetetramine（TETA） can be chelated with Cd²⁺, Hg²⁺and Pb²⁺. Because of theadvantages of the flocculant in water treatment, using the Mannich reaction principle, for theskeleton of the main chain of the polyacrylamide（PAM）, DETA and TETA graft up to theformation of a new type of flocculant, the experiments confirmed that the flocculant not onlyhas the ability of flocculation and sedimentation, but also has the ability of chelating Cd²⁺,Hg²⁺and Pb²⁺.By the single fator experiment in the synthesis of Amine grafted flocculant, we can knowthe best reaction conditions for synthesis of diethylene triamine is as follows:the solution pHwas adjusted to9, the temperature was set up to50℃, add1.4mL formaldehyde to100mL1%PAM and reaction1h, then add1.5mL DETA and reaction3h. The degree of reaction of theamine can reach34.26%. The best reaction conditions for synthesis of triethylene tetramine isas follows:the solution pH was adjusted to8, the temperature was set up to50℃, add1.3mLformaldehyde to100mL1%PAM and reaction1h, then add1.5mL TETA and reaction3h. The reaction of amination degree can reach33.73%.The new flocculant grafted by amine has the ability to chelating heavy meatal ions.While pH, temperature, initial concentration, stirring time and settling time conditions areidentified, the DETA clelating flocculant can remove95.3%cadmium,96.8%mercury,94.4%lead; the TETA clelating flocculant can remove96.4%cadmium,99.4%mercury,95.2%lead.The interference experiments show that the common inorganic ions won’t effect thereaction of removing heavy metal ions. That shows the new clelating flocculant has a goodselectivity to remove heavy metal ions. With a secondary removing exprements, theconcentration of cadmium was reduced to less than0.1mg/L, the concentration of mercurywas reduced to less than0.05mg/L, the concentration of lead was reduced to less than1mg/L.It can meet the requirements of the heavy metal ions from wastewater emission standards.In the experiments, the change of the structure of matterinfrared spectrum were identifiedby the infrared spectrum in the process of amine grafted flocculant synthesis and chelatingheavy metal ions, then it was confirmed that the flocculant chain linked with chelation groupsand the chelating flocculant could chelate and adsorpt the heavy metal ion.The experimental results demonstrated that the process of amino grafting flocculantadsorption heavy metal ions meet the process of Langmuir isothermal adsorption. And theisothermal adsorption equation and saturated adsorption of qmin all the adsorption processwere fitted on the basis of experimental data.Also, the saturated adsorption to cadmium,mercury and lead of the diethylenetriamine chelating flocculant was1.67mg/mL,1.67mg/mLand1.43mg/mL respectively, and the saturated adsorption to cadmium, mercury and lead ofthe triethylenetetramine chelating flocculant was1.43mg/mL,2mg/mL and1.43mg/mLrespectively.According to the thermodynamic theories, we could find that the activation energy of theprocess of amino grafting flocculant chelating heavy metal ions was56.67kJ/mol, then itcould be known that the process of amino grafting flocculant chelating heavy metal ionsbelonged to the chelating reaction process, and it could carry out more easily under normaltemperature. And the process of amino grafting flocculant chelating heavy metal ions was practicable from the point of view of soft hard acid-base theory. Meanwhile, the experimentalresults were tested and verified on the basis of soft hard acid-base theory and chelating stableconstants.Through the experiment, we could find the new method to remove heavy metal ion, also,get the new type of reagent of removing heavy metal ions. In the meantime, the reagent hasmany advantages, such as effective removal efficiency, easy operation, and low energyconsumption, provided new ideas and direction for heavy metal pollution of water treatment.