Properties Of Heavy Metal Chelating Flocculants With Polyacrylamide And Its Derivatives Modified By Mercaptoacetyl Reaction

When the water is contaminated by heavy metals,harmful substances will enter the human body through various ways,causing acute and chronic poisoning,which can threaten human health.Currently,chemical precipitation method is mainly adopted for the terminal treatment of heavy metal wastewater,but it has defects such as unsatisfactory treatment effect,poor sedimentation of sediments,large amount of sludge and heavy metal re-dissolution,etc.Therefore,seeking new treatment methods for heavy metal wastewater has become a research hotspot.In this thesis,polyacrylamide and its derivatives are used as precursors to prepare a series of new heavy metal chelating flocculants by chemical synthesis methods which introduce strong coordination group thiol groups of heavy metal ions into their molecular structures,including mercaptoacetyl polyacrylamide（MAPAM）,mercaptoacetyl aminomethy-polyacrylamide（MAAPAM）,mercaptoacetyl hydroxymethy-polyacrylamide（MAMPAM）and mercaptoacetyl sulfomethy-polyacrylamide（MASPAM）.The flocculants has the dual functions of chelation and flocculation and can be directly applied to the treatment of heavy metal wastewater.In this thesis,heavy metal chelating flocculants of thiol acetylated modified polyacrylamide and its derivatives are studied.The flocculation experiment are used to investigate the performence of flocculants for the removal of turbidity,copper and cadmium.The solution properties of flocculants,morphological characteristics of chelating flocs and stability constants of chelates are also discussed.The main results are given as follows.（1）Both MAPAM and MAMPAM are anionic heavy metal chelating flocculants while MAAPAM and MASPAM are amphiphilic macromolecular flocculant which isoelectric points is 8.8 and 2.2（distilled water system）respectively.The turbidity removal performance of MAAPAM is slightly inferior to the other three.When Fe（III）salt is present in the system,the highest removal rates of turbidity of MAPAM,MAAPAM,MAMPAM and MASPAM at their respective optimal dosage points are 94.7%,88.8%,94.0%,and 96.4%,respectively.Compared with the flocculants alone,the highest removal rate of turbility increases by 18%,11.8%,17.8%and 18.5%,respectively.（2）MAPAM,MAAPAM,MAMPAM and MASPAM have good removal performance for Cu（II）and Cd（II）in the water sample.When the pH value of the system is 6.0 and the concentration of heavy metal ions is 25 mg/L,for a single water sample containing Cu（II）.the highest removal rates of Cu（II）by MAPAM,MAAPAM,MAMPAM and MASPAM are96.0%,99.9%,96.3%,94.7%,respectively.For four flocculants,the trapping order of Cu（II）is that:MAAPAM>MAMPAM>MAPAM>MASPAM.For a single water sample containing Cd（II）,the highest removal rates of Cd（II）by MAPAM,MAAPAM,MAMPAM and MASPAM are 74.9%,73.7%,74.5%and 69.3%,respectively.The order of capture of Cd（II）by four flocculants is that MAPAM>MAMPAM>MAAPAM>MASPAM,For the mixed heavy metal system of Cu（II）and Cd（II）,the trapping order of the four flocculants is:Cu（II）>Cd（II）.（3）When MAAPAM is combined with polyethylamine sodium xanthate（PEX）to treat the water samples with Cu（II）initial concentration of 100 mg/L,the removal rate of Cu（II）is up to 99.6%).It can effectively solve the high processing cost due to the high treatment cost of PEX and the large dosage of MAAPAM.It can not only achieve the standard discharge,but also reduce the treatment cost,which is beneficial to practical applications.（4）The ultraviolet absorption characteristics of MAPAM,MAAPAM,MAMPAM and MASPAM to Cu（II）and Cd（II）are studied by ultraviolet spectroscopy.The results show that MAPAM,MAAPAM,MAMPAM and MASPAM have strong chelating ability to Cu（II）and Cd（II）.The sulfhydryl groups（-SH）and Cu（II）,Cd（II）are all formed stable chelates at 2:1.The stability constants of the chelates formed by MAPAM,MAAPAM,MAMPAM,MASPAM and Cu（II）is 6.0758×10¹²,6.9756×10¹²,6.8158×10¹²,6.0617×10¹²,respectively.The stability constants of the chelates formed by MAPAM,MAAPAM,MAMPAM,MASPAM and Cd（II）The constants is 7.3399×10¹¹,6.3544×10¹¹,7.0218×10¹¹,6.0141×10¹¹,respectively.（5）The coexistence of turbidity in the system promoted the removal of Cu（II）by MASPAM,while the coexistence of EDTA,sodium citrate and sodium pyrophosphate show an inhibitory effect on MASPAM capture of Cu（II）.The fractal dimension results of the chelated flocs show that the removal rate of the corresponding heavy metal ions is better with a larger the fractal dimension.