Preparation Of Heavy Metal Agent TDTC And Its Removal Characteristics Of Complex Heavy Metals

With the continuous development and progress of industrial technology,the problem of heavy metal wastewater pollution is becoming serious,and the excessive discharge into the environmental water body will cause serious pollution to the water.As an important source of heavy metal wastewater,the effective removal of complexed heavy metals present in electroplating wastewater is currently a difficult and hot research area.The general precipitation method has the problem of low removal rate for acidic and low concentration complexed heavy metal wastewater,and the development of efficient Dithiocarbamate（DTC）heavy metal traps is a feasible and effective method.In this study,a heavy metal chelator containing multiple dithiocarbamate groups was prepared and synthesized by a mild and rapid reaction method using triethylenetetramine and other raw materials,and named as TDTC.During the preparation process,the preparation process parameters were optimized through single-factor experiments such as sodium hydroxide dosage,carbon disulfide dosage,reaction time,reaction temperature and organic solvent ratio,and the best preparation process parameters were obtained as follows:the TDTC yield reached 82.27%at a sodium hydroxide dosage of 0.15 mol,n（CS₂）:n（TETA）=2.2:1,reaction time of 2.0 h,V glycol/V_H2O=1:1,and reaction temperature of25°C.TDTC was characterized and analyzed by scanning electron microscopy（SEM）,elemental analysis,infrared spectroscopy（FTIR）and X-ray photoelectron spectroscopy（XPS）,respectively.The characterization results showed that the heavy metal trap had successfully synthesized dithiocarbonyl groups,and the molecular formula of TDTC was also obtained as C₈S₄N₄H₁₆.TDTC was applied to the removal of complexed heavy metals from electroplating wastewater.In the study of treating various acidic complexed copper（EDTA-Cu,CA-Cu,TA-Cu）at a concentration of 50 mg·L^-1,the effects of TDTC dosing,initial p H,reaction time and flocculant dosage on the removal of various complexed copper were investigated.The experimental results showed that the removal rate of the three complexed copper was above 99.4%at a TDTC dosage of 1 mmol·L^-1,an initial p H range of 3～8,a reaction time of 3 min,and a flocculant addition of 1 mg·L^-1,which met the copper emission limit of the corresponding standard（GB21900-2008）.The effects of TDTC dosing,initial p H,reaction time,complexing agent concentration and coexisting ions on the removal of multiple complexed nickel（CA-Ni,TA-Ni,SP-Ni）at a concentration of 5 mg·L^-1were investigated.The experimental results showed that the removal rates of SP-Ni and CA-Ni were 99.56%and 99.23%,respectively,when the initial p H was 4～8,the reaction time was 4 min,and the TDTC dosage reached 80 mg·L^-1,and the removal rate of CA-Ni reached 97.89%at the dosage of 90 mg·L^-1,both of which were much smaller than the relevant emission limit of Ni(<0.1 mg·L^-1),the increase of sodium pyrophosphate and sodium tartarate concentrations had a certain promotion effect on complexed nickel removal,while the increase of citric acid concentration had a certain inhibition effect on removal.The chelating mechanism of trapping agent for complexed copper and nickel was studied by infrared spectroscopy（FTIR）,X-ray photoelectron spectroscopy（XPS）and elemental analysis,and the recovery of trapping precipitation was also investigated.The results of mechanism investigation show that the main mechanism of TDTC’s action on complexed Cu and Ni is to remove them by chelating them into insoluble chelate precipitates through the contribution of electrons from S and N atoms on the DTC functional group,and chelating them with the heavy metal ligands on the complexing agent.Nickel oxide can be recovered from the chelated precipitation of TDTC and complexed nickel by pyrometallurgical methods,and the recovered product has a high purity and recovery rate of more than 90%,so that the valuable metal can be recycled.