Performance And Mechanism For Removal Of Chromium And Copper By Dithiocarboxyl Aminomethy-Polyacrylamide

Chromium and copper are two heavy metal elements that are highly concentrated in water bodies,mainly originating from industrial enterprises such as electronics,non-ferrous metal processing,and mining,which discharge wastewater.Such wastewater not only contains a large amount of heavy metal ions but also numerous organic pollutants,mostly metal chelating agents such as ethylenediaminetetraacetic acid(EDTA),pyrophosphoric acid,and citric acid.These agents easily form stable complexes with heavy metals,making traditional methods of removing heavy metals ineffective.Therefore,to effectively remove water samples containing Cr(Ⅵ),Cu(Ⅱ),and Cu complexes while solving the problem of additional dosage of other chemicals required by traditional chemical precipitation methods,this study used dithiocarboxylic acid amine methyl polyacrylamide(DTAPAM)as a heavy metal flocculant.The study investigated the performance and mechanism of DTAPAM in removing water samples containing Cr(Ⅵ),Cu(Ⅱ),and Cu complexes under hydrodynamic conditions,DTAPAM dosage,pH value,inorganic substances,organic substances,initial concentration of heavy metals as factors.Characterization methods such as Zeta potential measurement,UV-visible absorption spectroscopy,infrared spectroscopy,scanning electron microscopy and energy spectrum analysis were used.The main research results are as follows:(1)DTAPAM exhibits excellent removal efficiency of Cr(Ⅵ)under weakly acidic conditions,with pH 3.0 being the optimal initial pH value.However,the removal efficiency of total Cr by DTAPAM under different pH values is unsatisfactory.(2)DTAPAM demonstrates significant removal efficiency for water samples containing different initial concentrations of Cr(Ⅵ)(at pH 3.0).The maximum removal rates for water samples containing Cr(Ⅵ)with initial concentrations of 5mg/L,15mg/L,25mg/L,and 50mg/L are 92.75%,93.75%,97.28%,and 96.73%,respectively.(3)Inorganic cation Fe3+ significantly enhances the removal of both Cr(Ⅵ)and total Cr by DTAPAM.The maximum removal rate for total Cr is achieved through the complexation of DTAPAM and Fe Cl3 at a rate of 63.32%.(4)In a system where turbidity coexists with Cr(Ⅵ),turbidity inhibits the removal of Cr(Ⅵ)by DTAPAM,which slightly increases as turbidity increases.Except when the original turbidity is at 20 NTU and when the amount of added DTAPAM ranges from 60-270mg/L,turbidity significantly promotes the removal of total Cr by DTAPAM(increasing as turbidity increases).(5)The mechanism behind DTAPAM’s removal of Cr(Ⅵ)includes redox reactions,chelation precipitation,and flocculation sedimentation.(6)DTAPAM exhibits not only a good removal efficiency towards free Cu(Ⅱ),but also a high removal rate towards complexed Cu(Ⅱ).The maximum removal rates of Cu(Ⅱ)from EDTA-Cu,citric acid-Cu,and pyrophosphate-Cu by DTAPAM are 99.07%,99.44%,and 100%,respectively.(7)The pH value has a significant impact on the removal of Cu complexes by DTAPAM.Under highly acidic or alkaline conditions,the removal rate of Cu(Ⅱ)is relatively low.The optimal initial pH values for the removal of EDTA-Cu and citric acid-Cu by DTAPAM are 7.0,while the optimal initial pH value for the removal of pyrophosphate-Cu is 6.0.(8)The pH value has a minor effect on the chelation stability of DTAPAM-Cu.When the pH value ranges from 2.0 to 9.0,the logarithmic value of the chelation stability constant of DTAPAM-Cu ranges from 13.09 to 13.71,and lg K decreases as pH increases,changing from a positive to negative value.(9)When treating water samples containing Cu complexes with DTAPAM,DTAPAM competes with organic ligands for coordination with Cu(Ⅱ).This results in the formation of flocs that precipitate with Cu(Ⅱ)in organic ligands through chelation reactions.The flocs undergo coagulation mainly through adsorption bridging and net trapping and rolling effects between them,which promotes their sedimentation and enhances the removal efficiency of Cu(Ⅱ).