Study On Disposal Of Pb²⁺ And Zn²⁺ In Wastewater By Macromolecular Heavy Metal Flocculant CSAX

A novel macromolecule flocculant with the function of trapping turbidity and removing heavy metal ions has been synthesized by using corn starch as matrices through cross-linking, graft copolymerization and sulfonation reaction. The flocculant called Crosslinked Starch-graft-poly Acrylamide-co- sodium Xanthate?CSAX?.The structures of CSAX were characterized with fourier transform infrared spectroscopy?FTIR?, scanning electronic microscope?SEM?, and Energy dispersive X-ray spectrometry?EDS?. CSAX as a flocculant, has the high efficiency for the removal of Pb²⁺ and Zn²⁺ in waste and wastewater from lead and zinc smelter through flocculation test.There are six sections of experimental studies in the thesis :We conducted the experiment to investigate the molecular structure of CSAX and its molecular shape, and the removal efficiency in lead and zinc wastewater treatment by detecting pH, turbidity, heavy metal ion and coexisting ions concentration. The result showed that CSAX can remove 95% Pb²⁺ and 83% Zn²⁺, indicating the binding capabilities of CSAX to remove Pb²⁺ and Zn²⁺. pH value significantly influence on the removal rate of Pb²⁺ and Zn²⁺. Specifically, the removal rate increase with the increase in pH value in the range of pH<7.Turbidity can promote the removal rate of Pb²⁺ and Zn²⁺ under conditions. There is a stoichiometric relationship between heavy metal and CSAX due to the chelating reactions. Greater initial concentration of Pb²⁺ and Zn²⁺ contributed to the higher removal rate by the chelating reaction between heavy metal ions and flocculants. Alkali metal and alkaline-earth metal have no influence of the remove rate. Anion with weak coordination ability will not impact on the removal of Pb²⁺ and Zn²⁺. EDTA inhibit the removal rate of Pb²⁺ by CSAX. Low dosage of humic acid can promote the removal rate of Pb²⁺.Based on the single factor experiment, different response surface experimental designs were used to optimized CSAX to remove Pb²⁺ and Zn²⁺ conditions.The model fitting degree was good,and the model was significant. Experiments proves the effectiveness and validity of the designed method.To improve elimination of Zn²⁺ in wastewater by enhanced coagulation with CSAX and modified attapulgite clay as coagulant aid.The effects of modified attapulgite clay preparing conditions were studied.Response surface optimized enhanced coagulation conditions.The result showed that the modified attapulgite clay used as assistant coagulants improved the removal of Zn²⁺ efficiently.CSAX was applied to the actual wastewater to verify the applicability. It showed that less-polluting industrial waste once flocculation experiments can make the concentration of heavy metals in the effluent standard,while high-polluting industrial waste required a multi-stage flocculation experiments to effluent standards.The microscopic studies of CSAX flocs indicated that CSAX flocs' surface and interior presented highly irregularity.The research also indicated that CSAX flocs' structure and establishment possessed fractal characteristics.The influence CSAX dosage, pH and concentration of heavy metal ions to form floc fractal dimension were studied.The results showed that at the optimum dosage, the optimum pH value, and a suitable heavy metal ion concentration, floc shape most irregular, the largest surface area, pore maximum fractal dimension who was the greatest, the highest removal rate accordingly.Stabilization of product and feasibility of heavy metals recycling were discussed. It can be seen that CSAX-Pb and CSAX-Zn floes in the water fairly stable and will not cause secondary pollution.With a strong acid soak floc, heavy metal leaching rate of 80%, indicating that recovery of heavy metals in the floc is feasible.