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 C-13 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 Delta H degrees, Delta S degrees and Delta G degrees were also calculated to prove the adsorption process being exothermic and spontaneous. (C) 2012 Elsevier Ltd. All rights reserved.