| As an important source of heavy metal wastewater, the reasonable treatment of electroplating wastewater has been noticed by many researchers.Especially, with increasingly strict for electroplating wastewater emission regulations, the removl of cmplex heavy metal from wastewater has became a hot issue.Dithiocarbamate (DTC) as a kind of heavy metal capturing agent, has performed superior effectiveness in treatment of heavy metal ions, but the capture has a poor effectiveness in acidic condition. The paper aims to research and synthesize an effective multi-dithiocarbamate heavy metal capturing agent, and it was utilized for removing acid complex copper ions and trace complex nickel ions from wastewater.In this work, a multi-dithiocarbamate heavy metal chelating agent of N,N’-bis(2-mercaptoethyl)ethylenediamine (EDTC) was prepared using ethylenediamine and carbon disulfide as raw materials, and mixed solution of anhydrous ethyl alcohol and deionized water as solvent. The productivity of EDTC was evaluated according to organic solvent dosage, raw materials cusumption, reaction time, and reaction temperature through single factor experiments.The optimum synthetic conditions are obtained as follows: volume ratio of ethanol and deionized water was 1:2 in the mixed solvent, molar ratio of ethylenediamine to carbon disulfide was 1:2.5, reaction temperature was 25℃, reation time was 2.0 hour,and the productivity of EDTC was about 82.39%. The structure of EDTC wasconfirmed by ultraviolet spectra, Fourier transform infrared spectra, and elemental analysis. The result showed that the DTC group was formed in EDTC, while the molecule formula was N2C4H8S4. EDTC was insoluble in organic solvent, slightly soluble in water,but soluble in NaOH solution.And its melting point was 158℃.Then the simulated wastewater of acid complex copper ions and trace complex nickel ions were treated by EDTC, respectively. The removal performance of heavy metal wastewater by BDE was investigated according to EDTC dosage, initial concentration, pH, and reaction time through single factor experiments. The results showed that:50 mg/L of initial copper concentration, pH 3～9, MEDTC/MCu=8,3min of reaction time,1.0 mg/L of the coagulant aid (PAM) dosageand slower stirring for 3min, lead to less than 0.25 mg/L of residual Cu2+concentration with the removal rate of 99.5%. With the optimum conditons of dosages of EDTC are 60 mg/L,55 mg/L and 70 mg/L, respectively, pH 4～8,2min of reaction time and 1.0 mg/L of PAM dosage. The residual Ni2+ concentration could be decreased to less than 0.05 mg/L from the initial concentration of 5.0 mg/L, and the corresponding removal efficiency of Ni2+was more than 99%. And the residual concentrations of Cu2+ and Ni2+were all meeting the special emission limit of the emission standard of pollutants for electroplating of China EPA’s regulation.After that, Fourier transform infrared spectra and elemental analysis were applied to research the reaction mechanism between EDTC and acid complexing copper or nickel. The results showed that:the chelate reaction could take place between EDTC and heavy metal ions, Cu2+ or Ni2+was directly captured from its corresponding complex, forming an insoluble chelation with EDTC. Therefore the Ni2+ was removed efficiently. Besides, the stability and sedimentation property of chelated precipitates was also discussed, the SDLT results shown that EDTC-Cu and EDTC-Ni were all non-hazardous and stable in weak acid and alkaline conditions. |
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