Heavy Metal Complexes Wastewater Treatment with Chelation Precipitation

In view of the existing technical problems about treatment of electroplating wastewater , the new technology of processing electroplating wastewater with organic heavy metal chelator-dithiocarbamates is developed. Using electroplating wastewater containing copper, nickel and chromium complexes with EDTA, ammonia and citric acid as an example, this study investigated the reaction mechanism and influencing factors of heavy metal removal efficiency from metal complexes using dithiocarbamates. The stability of chelating complexes was evaluated. Results showed that the chelator could remove copper, nickel and chromium up to 99% when the concentrations of copper, nickel, and chromium ions were 63.55, 58.69, and 52.00 mg/L, respectively. The effluent water after the treatment met with the concentration limitation of Integrated Wastewater Discharge Standard (GB8978-1996). Coexistence of these heavy metal complexes did not affect the efficiency significantly. Because chelator can be used directly to treat acidic wastewater containing heavy metals, it is unnecessary to destroy the constitution of metal complexes preliminarily, and therefore the cost for pH adjustment can be saved and the treatment process can be simplified. The leaching-out concentrations of heavy metal ions from the treatment with chelating complex were much lower than that of treatment with metal hydroxides, and below the concentration limitation in the Standard for Pollution Control on the Security Landfill Site for Hazardous Wastes (GB18598-2001).