Study On Synthesis And Performance Of Poly (Diallyl Methyl Hydroxypropoxy Ammounium Chloride)-based Dithiocarbamate Sodium

Heavy metal wastewater pollution is a great threat, whether to environment or to human.Heavy metal pollution incidents occur repeatedly, which indicates that it is very urgent to treatpolluted water. Compared with other heavy metal wastewater treatments, the chelatingprecipitation posses a simple process, good treatment effect, especially suitable for thetreatment of large volumes of heavy metal wastewater. The key is the performance ofchelating flocculant. Given the problem that the charge neutralization effect cannot achievethe best resulting from the uneven distribution of positive charges on macromolecule chainsof an amphoteric chelating polymer flocculant (ACPF) based onpoly(dimethyldiallylamonium chloride-acrylamide) designed and synthesized by our researchgroup early, a novel amphoteric chelating polymer flocculant of poly(diallyl methylhydroxypropoxy ammounium chloride)-based dithiocarbamate sodium (PDAMHACDTC)was designed and synthesized. The synthesis conditions for PDAMHACDTC, its structure,chelation-flocculation properties and application performance were also investigated.(1) PDAMHACDTC was synthesized by using diallylmethylamine (DAMA),epichlorohydrin (ECH), triethylene tetramine (TETA), NaOH and CS2as raw materials, andthe suitable synthetic conditions for PDAMHACDTC were determined. The syntheticconditions for diallyl methyl epoxypropyl ammonium chloride (DAMEPC) are as follows:n(ECH)∶n(DAMA)=1.02∶1, reaction time7h, and reaction temperature60℃. Thesynthetic conditions for diallyl methyl hydroxypropyl multi-amidocyanogen ammonium(DAMHAC) are as follows: n(TETA)∶n(DAMEPC)=1～1.05∶1, reaction time6h, andreaction temperature80℃. The synthetic conditions for poly(diallyl methyl hydroxypropylmulti-amidocyanogen ammounium chloride)-based dithiocarbamate sodium (PDAMHAC)are as follows: c(DAMHAC)≥2.3mol/L, m(AIBA)/m(DAMHAC)=0.01:1, reaction time9h,and temperature70℃. And the appropriate synthetic conditions for PDAMHACDTC are asfollows: n(DAMHAC)∶n(NaOH)∶n(CS2)=1∶3.9∶3, reaction time3h and temperature25℃at the first stage, and reaction time1.5h and temperature45℃at the second stage. Thestructures of PDAMHACDTC were characterized by elemental analysis, FT-IR, NMRspectroscopy and ultravoilet spectroscopy, showing that the PDAMHACDTC has beensynthesized successfully.(2) The removal performances of PDAMHACDTC towards Cu2+, Ni2+, Zn2+, Pb2+, Cd2+,Hg2+and Mn2+were investigated, and the mechanism of chelation–flocculation was exploredpreliminarily. The results show that, when the molar ratios of–CSS–to Cu2+, Ni2+, Zn2+, Pb2+, Cd2+, Mn2+are all close to2:1, and the molar ratios of–CSS–to Hg2+is close to1:1, theremoval rates for these heavy metal ions at a wide pH scope are higher, and the residual heavymetal concentrations are all below the limit set by the China’s Integrated WastewaterDischarge Standard (GB8978-1996). When Cu2+、Ni2+、Zn2+、Cd2+and Mn2+coexist inwastewater, PDAMHACDTC has selectivity for different heavy metal ions, and the generalselectivity order is Cu2+＞Cd2+＞Mn2+＞Zn2+＞Ni2+.(3) The volumes of flocs produced by PDAMHACDTC are larger and their settlingcharacteristics are better than those produced by ACPF. The main reason is that eachmonomeric unit of PDAMHACDTC has a positive charge, the positive charges are distributedmore uniform than those of ACPF, therefore, PDAMHACDTC is more conducive toneutralize the excessively negative charges on micro-flocs than ACPF. This point is embodiedin that the higherζpotential of micro-flocs by PDAMHACDTC than those by ACPF at thesame–CSS–dosage. So it is conducive to promote the formation and growth of micro-flocs,and improve flocs′s structure, thus enhance chelation-flocculation effect.(4) The zinc sulfate wastewater was treated by PDAMHACDTC in combination withNa2CO3. The results show that when the value of pH is7～10.4, and Na2CO3dosage is0.6g/L, and PDAMHACDTC dosage is1.7g/L, the residual concentrations of Zn2+, Cd2+, Ni2+and COD can all achieve the first grade criteria of China’s Integrated Wastewater DischargeStandard. Using PDAMHACDTC to treate electroplating wastewater, when the value of pH is6.7～10.2, and PDAMHACDTC dosage is1.0g/L, the residual Cu2+, Ni2+and CODconcentrations of the treated water are all lower than the Emission standard of Pollutants forElectroplating (GB21900-2008).In summary, PDAMHACDTC designed and synthesized in this study has a positivecharge on every monomeric unit of the macromolecule chain, so the positive charges aredistributed uniformly. Therefore, PDAMHACDTC can neutralize more effectively theexcessive negative charges on the micro-flocs, and is beneficial for promoting the formationand growth of flocs, and improving the flocs′s structure, thus enhancing its chelating abilitiesand flocculation and settling performance. This study has solved the problem that the unevendistribution of positive charges on ACPF, so the PDAMHACDTC synthesized can remove theheavy metal ions more effectively.