Disodium N,N-bis-(dithiocarboxy)ethanediamine: synthesis, performance, and mechanism of action toward trace ethylenediaminetetraacetic acid copper (II)

A new effective multi-dithiocarbamate heavy metal precipitant, disodium N,N-bis-(dithiocarboxy) ethanediamine (BDE), was synthesized by mixing ethanediamine with carbon disulfide under alkaline conditions, and it was utilized for removing trace ethylenediaminetetraacetic acid copper (II) (EDTA-Cu) from wastewater. Its structure was confirmed by ultraviolet spectra, Fourier transform infrared spectra, scanning electron microscopy, thermogravimetric analysis, and elemental analysis. The removal performance of EDTA-Cu by BDE was evaluated according to BDE dosage, initial concentration, pH, and reaction time through single-factor experiments. With the optimized conditions of a pH range of 3–9, dosage ratio of BDE/Cu of 1:1, PAM dosage of 1 mg/L, and reaction time of 4 min, the removal efficiency of Cu 2+ was more than 98 % from simulated wastewater containing EDTA-Cu with initial concentrations of 5–100 mg/L. Treatment of actual EDTA-Cu wastewater showed that BDE performed superior effectiveness, and the average residential concentration of Cu 2+ was 0.115 mg/L. Besides, the stability of chelated precipitate and the reaction mechanism of BDE and EDTA-Cu were also introduced. The toxicity characteristic leaching procedure (TCLP) and semi-dynamic leaching test (SDLT) indicated that the chelated precipitate was non-hazardous and stable in weak acid and alkaline conditions. The BDE reacts with EDTA-Cu at a stoichiometric ratio, and the removal of Cu 2+ was predominantly achieved through the replacement reaction of BDE and EDTA-Cu.