Preparation And Performance Of Polydithiocarboxyl Acrylamide Used As Macromolecular Heavy Metal Flocculant

The heavy metal wastewater contains a large amount of copper and chromium,which is one of the main causes of water environment destruction,and these heavy metals can be enriched by organisms easily,which will be harmful to human and aquatic organisms.The traditional chemical precipitation method is a common method for treating heavy metal wastewater due to its low cost,mature technology and convenient management.However,it also has the disadvantages of unstable removal effects and producing a large number of sludges.So it has been a hotspot for scholars to develop a kind of more efficient heavy metal processing material which can make full use of the existing processing units of the traditional chemical precipitation method.Polyacrylamide（PAM）is often used as a coagulant in water treatment to remove granular and colloidal contaminants from wastewater,while it can not remove dissolved heavy metal ions.Based on this,if the strong ligand groups of heavy metal ions could be grafted onto the PAM molecular chain,it would simultaneously remove the heavy metals and the turbidity.In this paper,acrylamide（AM）,carbon disulfide（CS₂）and sodium hydroxide（NaOH）are used as the raw materials to prepare the intermediate product dithiocarboxyl acrylamide（DTAM）with the ability to capture heavy metal ions,and a novel heavy metal flocculant polydithiocarboxyl acrylamide（PDTAM）is prepared by polymerizing the intermediate product DTAM with AIBI as the initiator.The main influencing factors during the preparation of PDTAM are confirmed by single factor experiments and the optimal preparation conditions are determined by orthogonal experiments.The solution characteristics,isoelectric point and storage stability of PDTAM are studied.The composition and structure of PDTAM are characterized by elemental analysis and infrared analysis,the weight-average molecular weight of PDTAM is measured by multi-angle laser light scattering instrument.The removal efficiencies on Cu²⁺,Pb²⁺and turbidity of PDTAM are studied by flocculation experiments.The stability constant,stability and recovery of chelating flocs are determined.The infrared spectroscopy,scanning electron microscopy and X-ray spectrometer are used to study the structure,surface morphology and chemical composition of flocs.The main experimental results are as follows:（1）The optimal conditions for the preparation of PDTAM are obtained by the single factor experiments and the orthogonal experiments,the removal rates of Cu²⁺and Pb²⁺in water samples are taken as the index,the mixed reaction time t₀ is 30 min,the mixed reaction temperature T₀ is 20°C,the AM mass concentration is 5%,the reactant ratio[n（NaOH）:n（CS₂）:n（AM）]is 2:2:1,the pre-reaction temperature T₁ is 35°C,the pre-reaction time t₁ is 60min,the main reaction temperature T₂ is 50°C,the main reaction time t₂ is 150 min,the initiator AIBI dosage is 0.24 g,the polymerization temperature is 60°C,and the polymerization time is 18 h.（2）The chemical composition and structure of PDTAM are characterized by elemental analysis and infrared analysis,indicating that the dithiocarboxyl group is successfully grafted onto the PDTAM molecular chains.The molecular weight of PDTAM is determined by multi-angle laser light scattering instrument.The weight-average molecular weights are 3.530×10⁴g/mol and 3.485×10⁴g/mol,respectively,indicating that the final product PDTAM is successfully synthesized by polymerizing the intermediate product DTAM.（3）PDTAM has good treatment effects on water samples which contains different concentrations of Cu²⁺or Pb²⁺,and there is an optimal dosage.The removal performance of PDTAM is poor with the water samples containing Cu²⁺,when the pH is too high or too low.When treating water samples containing Pb²⁺,the removal performance of PDTAM is better at a higher pH value.The presence of EDTA,sodium citrate（SC）,sodium pyrophosphate（TSPP）and turbidity in simulated wastewater can have inhibiting or promoting effects on the heavy metal ions removal with PDTAM.The presence of turbidity substances can promote the Cu²⁺and Pb²⁺removal,and PDTAM can effectively reduce the turbidity in the system while removing heavy metal ions.（4）The structure,chemical composition and surface morphology of the flocs PDTAM-Cu and PDTAM-Pb are characterized by infrared spectroscopy,scanning electron microscopy and X-ray spectrometry,indicating that the dithiocarboxy groups have reacted with the heavy metal ions.The stability of chelating flocs PDTAM-Cu is good,PDTAM-Cu has almost no leaching in weak acid,neutral and alkaline environments.The recovery performances in hydrochloric acid,sulfuric acid and nitric acid recovery liquids are good.The chelating floc PDTAM-Pb has good stability in weak acid,neutral and alkaline environments.The recovery performances in hydrochloric acid and nitric acid solution are good while in sulfuric acid recovery liquid the recovery performance is poor.The chelation constants of the two flocs are determined by Unicam UV300 UV-Vis spectrophotometer.The results show that the ratio of-CSS^-to Cu²⁺and Pb²⁺is 2:1,and the stability constants of the chelating flocs PDTAM-Cu and PDTAM-Pb are 1.58×10¹22 and 3.47×10¹²,respectively.（5）The macromolecular heavy metal flocculant PDTAM is applied to the smelter wastewater and electroplating wastewater,respectively,which shows that PDTAM has good Cu²⁺removal effects,and the turbidity of the system is significantly reduced,which indicates that PDTAM has a good application prospects.