Reaserch On The Treatment Of Heavy Metal-containing Wastewater By Flocculation And Adsorption

This paper mainly gives a detailed description of the processing method of thepollutants of heavy metal and research development of flocculating agent, it alsoprospects the research direction of the processing method of the pollutants of heavymetal.This thesis makes a synthesized analysis of the pollutants of heavy metal whichis requested to deal with by this experiment, according to the requested processingeffect, and combining with the characteristics of various processing methods, which isa treatment process using chemical and physical method and then membraneseparation technology. At the pretreatment stage, it mainly researches two kinds ofprocessing methods, Coagulaton and sedimentation and chitosan-adsorption, and itused the single factor experiment and orthogonal test to determine the best conditionof these processing method, and then, to choose the best processing method, bycomparing their processing effects and economic effects.The pollutants used in this experiment contains cadmium, lead, copper and zincand their density are2mg/L,5mg/L,50mg/L and60mg/L, and their turbidity reachabout450NTU, according to some iron and steel enterprises’ characteristics ofsmelting pollutants, which is configured by Cu(NO3)2·6H2O, Zn(NO3)2·6H2O,Pb(CH3COO)4·3H2O,Cd(NO3)2·4H2O and kaolin.The method of coagula-ton and sedimentation mainly uses PFS and PAM asflocculating agent to deal with simulated compound pollutants of heavy metal, and itsprocessing effect is good. The best condition of processing method defined by singlefactor experiment and orthogonal test is that: reaction PH value of pollutants is9, theinput quantity of polymeric ferric sulfate(PFS) and polyacrylamide(PAM) are250mg/L and5mg/L, in the fast mixing process, the mixing speed is140rpm, the timeof mixing is4min, yet in the slow mixing process, mixing speed is60rpm, the time ofmixing is15min, after this, the density of lead and copper can not be checked by theatomica orption ectrophotomete, and density of cadmium and zinc respectivelyreaches0.027mg/L and0.056mg/L, both of them have reached the nationalrequested emission standard, more over, after this process, the turbidity of pollutantsis lower than10NTU, and their pH value are near to neutral. However, the density ofcadmium hasn’t reached the iron and steel enterprises’ requested standard of sewagerecovery. The method of chitosan-adsorption can eliminate simulated compound pollutantsof heavy metal, and the operation process is brief, the best condition of processingmethod defined by single factor experiment and orthogonal test is that: reaction pHvalue of pollutants is8, the input quantity of chitosan is200mg/L, adsorption time is40min, after this, the density of lead and copper can not be checked by the atomicaorption ectrophotomete, and density of cadmium and zinc respectively reaches0.031mg/L and0.062mg/L. The density of this four heavy metalions all have reached thenational emission standard, the turbidity of pollutants is lower than10NTU and thepollutants is neutral, but the density of cadmium is a little higher than the iron andsteel enterprises’ requested standard of sewage recovery.Through the economic analysis of this two pretreatments, it can be found that, byusing the method of coagula-ton and sedimentation, the cost of dealing with thepollutants of1m3is about0.37yuan, however, by using the method ofchitosan-adsorption, the cost is53.52yuan. We can see clearly that cost of the lattermethod is more expensive.