Study On Removal Of Heavy Metal Complexes In Water By Discharge Plasma

In recent years,the degradation of complex heavy metals has become a research hotspot in the field of electroplating and printing wastewater treatment due to its strong toxicity and non-biodegradability.The complex heavy metal has a very strong complexing ability compared to the free heavy metal ion in water.The removal effect by the traditional alkaline precipitation method is often not obvious,and the degradation mechanism is still unclear.As a typical advanced oxidation technology,the degradation of complex heavy metals has been widely studied due to its high efficiency and green cleaning by discharge plasma.Therefore,this study is proposed to degrade heavy metal complexes in water by using the discharge plasma technology.In the experiment,natural heavy metal complexes?Cu-HA?and artificial heavy metal complexes?Cu-EDTA?were used as target pollutants.The degradation rules of two target pollutants in the discharge system were evaluated,and the possible degradation ways were proposed.The removal performance of Cu-EDTA was improved by“iron powder discharge plasma”system,and the reaction mechanism was analyzed.Provide theoretical data for the engineering application of complex metal heavy metal removal process in water.The main results are as follows:Firstly,the effects of discharge voltage on the typical heavy metal complex Cu-HA,solution p H,and pollutant properties on the degradation of Cu-HA were investigated.The experimental results show that the removal rate of Cu-HA reached86.1%after treatment at a discharge voltage of 18 k V and a p H of 9.0 for 50 min.Appropriately increasing the voltage can promote the degradation of Cu-HA,and p H is the alkaline environment to help the degradation of Cu-HA.Then,the degradation process conforms to the first-order kinetic model.From the two aspects of free radical trapping experiment and quantitative determination of active substances,the contribution size and action law of oxidative active substances were explored.The results of the study indicate that O₃,H₂O₂,·OH,¹O_2,and O₂·^-generated during the reaction to remove Cu-HA,·OH is the main free radical.Through UV-vis,EEM fluorescence,Zeta potential,particle size analysis,ATR-FTIR,GC-MS,ion chromatography,and other analytical methods to speculate the possible degradation pathway of Cu-HA.Studies have shown that the active substances?including O₂·^-,¹O₂,and·OH?generated by the discharge plasma attack the carboxyl and hydroxyl functional groups of HA,causing the Cu-O bond to break,the Cu-HA to decompose and release free Cu²⁺.In addition,the results of toxicity experiments show that the high-efficiency degradation of Cu-HA by discharge plasma significantly reduces its biological toxicity to Scenedesmus obliquus?SO?.Secondly,the effects of initial concentration and p H of Cu-EDTA on its degradation of heavy metal complex Cu-EDTA was analyzed.The experimental results found that the initial concentration of Cu-EDTA was 0.3 mmol L^-1 and the p H was 2.0 as the best conditions for the experiment,too high initial concentration and the solution environment of peracid or alkali were not conducive to the degradation of Cu-EDTA.From the analysis of the action of active substances,it was found that both O₂·^-and·OH contribute to the degradation effect of Cu-EDTA.The surface morphology of Cu-EDTA was analyzed by AFM,TOC,DOC,FTIR,XRD,and XPS.The possible degradation pathways and mineralization rules of Cu-EDTA were proposed by the surface morphology analysis,mineralization law,and precipitation composition..The experimental results show that free radicals attack the Cu-EDTA macromolecules,and the decarboxylation reaction leads to the breaking of the Cu-O and Cu-N bonds,and further reacts with each other to generate small molecules such as organic acids.Thirdly,a discharge plasma-iron powder combined system was constructed by adding iron powder to treat Cu-EDTA.The influence of the amount of iron added by Cu-EDTA in the combined system on the degradation effect of Cu-EDTA was investigated.The strengthening mechanism of“displacement-Fenton-flocculation”was explored.Then,the preliminary mechanism of the synergistic system was revealed with the help of FTIR,EEM,GC-MS,IC,SEM,XRD,and Raman characterization methods.The precipitation products were studied.The results of the study found that when the amount of iron powder added was 2.0 g/L,the removal rate of Cu-EDTA could reach nearly 100% after 2 min of treatment.