Characteristics of heavy metals capturing agent dithiocarbamate (DTC) for treatment of ethylene diamine tetraacetic acid–Cu (EDTA–Cu) contaminated wastewater

An efficient and water-soluble (102 g/kg at 293 K) heavy metals capturing agent was developed for removal of copper in ethylene diamine tetraacetic acid–Cu (EDTA–Cu) wastewater. The agent was synthesized through nucleophilic reaction of carbon disulfide and hydrazine hydrate. Infra-red, ultraviolet and 13C Nuclear Magnetic Resonance (NMR) spectra and elemental analysis demonstrated that the agent was one of Tetrathio Bicarbamic Acid (C2H4N2S4) containing dithiocarbamate groups and was named DTC–TBA for short. Effect of DTC–TBA dosage, pH, reaction time, flocculant polyacrylamide (PAM) dosage and temperature on Cu2+ removal efficiency was investigated through single factor batch jar experiment for treatment of simulated EDTA–Cu wastewater with DTC–TBA. The optimized condition was pH of 3–5, molar ratio of DTC–TBA/Cu of 1.2:1, reaction time of 3 min, and PAM dosage of 2–6 mg/L. The removal efficiency of Cu2+ was greater than 99% with initial concentration of 100–1000 mg/L, and the maximum adsorption capability with DTC–TBA towards Cu2+ was 287.05 mg/g. Treatment of actual EDTA–Cu wastewater showed that DTC–TBA was efficient and average concentration of residential Cu2+ was 0.372 mg/L. These results indicated that DTC–TBA was stable in acidic condition and promising for application even when pH was below 3. Cu2+ was replaced by DTC–TBA at a stoichiometric ratio from EDTA–Cu. The adsorption kinetics and isotherm data could be well elucidated with pseudo-second-order equation and Langmuir model respectively. Thermodynamic parameters, involving ΔHO, ΔSO and ΔGO were also calculated to prove the adsorption process being exothermic and spontaneous.

► Efficient and water-soluble heavy metals capturing agent.
► High adsorption capability for Cu2+ from EDTA–Cu wastewater.
► Possessing more effective performance than other DTC-type agents at pH below 3.
► Deepened discussion of reaction mechanism from adsorption process and structure.