Preparation Of Heavy Metal Chelating Agent RDTC And Investigations On Its Performance Of Treatment Of Heavy Metal Wastewater

A dithiocarbamate heavy metal chelating agent RDTC was synthesized with tetraethylenepentamine,1,2-dichloroethane, CS2and NaOH at normal conditions. RDTC was characterized by IR and UV spectra. When the sulfur contained is29.5%, the agent’s performance was improved effectively by adding5%N,N’-bis-(dithiocarboxy) piperazine (BDP) to complex with RDTC.The treatment efficiencies of free ions and complex copper(II), nickel (II) and lead (II) simulated wastewaters by RDTC were investigated. Effects on the removal of heavy metal was also investigated including the dosage of RDTC, the pH and turbidity of wastewater; the performance of RDTC to decreasing turbidity, the sedimentation performance of resulting floc and the stability of precipitates was also investigated. The treatment of mixed and real heavy metal wastewater (HEDP pre-electroplating copper wastewater) was carried out with RDTC.The experimental results showed the results as follows:1. The optimized dosage of RDTC to treat wastewater containing50mg/L free Cu2+ions or25mg/L free Ni2+ions or100mg/Lfree Pb2+was13.6,7.6and8.4mL/L respectively. After the treatment, the residual metal ion concentration was Cu2+0.033,Ni2+0.043and Pb2+0.071mg/L, which completely met the Integrated Wastewater Discharge Standard (GB8978-1996).2. To treat the complex heavy metal wastewater, in order to make the residual heavy metal ion at the same level as the treatment of free ions, the optimized dosage of RDTC should be increase. The increased dosage was12%to treat CuEDTA wastewater, CuCA (citric acid, CA)、NiCA、NiTA(tartaric acid,TA)and PbCA was6%、0%、5%and8%respectively.3. The selectivity of RDTC was good, the sequence of RDTC was Cu2+>Pb2+>Cd2+>Ni2+4. The appropriate pH ranges of Cu2+, Ni2+and Pb2+wastewater were pH≥3, pH>5and pH>4respectively.5. The substance causing turbidity was favorable for the removal of heavy metal ions, which could be eliminated by RDTC with heavy metal ions together.6. The initial pH of wastewater presented great effect on the performance of resulting floc. To free Cu2+ions, CuCA and CuEDTA, the optimized pH was about5,7 and6respectively; To free Ni2+ions, NiTA and NiCA, the optimized pH was about4,9and7respectively; To free Pb2+ions and PbCA, the optimized pH was both about5. Besides, adding Al2(SO4)3could improve sedimentation performance effectively.7. The precipitates produced from the complex of RDTC with heavy metal were highly stable both in weak acidic and alkaline environment.8. To treat theHEDP pre-electroplating copper wastewater, RDTC could remove the Cu2+ions and met the Integrated Wastewater Discharge Standard (GB8978-1996).