Prepauration Of Heavy Metal Capturing Agent DTC-U And Its Application

As society progresses, the environment pollution is increasing. Human health and ecological balance are threatened by heavy metal wastewater due to its special hazards. Dithiocarbamate (DTC) as a kind of heavy metal capturing agent, has good capture effect to heavy metals, but the capture effect is poor when used in acidic conditions. The paper aims to research and develop a new type of DTC metal capturing agent, and expect to use it in treatment of heavy metal wastewater in acidic environment. The main research contents are as follows:(1) In this study, a new heavy metal capturing agent containing DTC is synthesized by using urea and carbon disulfide, which is named DTC-U. The effects of raw materials consumption, reaction time, temperature on productivity are investigated. The optimum synthetic conditions are obtained as follows:molar ratio of urea to carbon disulfide to sodium hydroxide is1:2.2:2.2, volume ratio of carbon disulfide to ethanol equals1:1.5, reaction temperature is35℃, and reaction time3hours. DTC-U is characterized by infra-red spectrum, the result confirm that the DTC group is formed in the molecule. The solubility experiment show that DTC-U is highly soluble in water and insoluble in common organic solvents such as ethanol and acetone. The melting point determined by verification regulation of melting-point-measuring instruments with capillary method is108℃.(2) DTC-U is used to treat the wastewater containing Pb2+, Cd2+, Cu2+separately. The effects of dosage, pH, reaction time, flocculating agent on removal rate are investigated. The results show that the three types of wastewater can meet the request of the criterion (GB25466-2010) under the experiment conditions of pH=5, room temperature, dosage of DTC-U about20mg/L,40mg/L,45mg/L separately, dosage of PAC and PAM used as flocculating agent about100mg/L and5mg/L respectively, reaction time8to12minutes.(3) The capture ability of DTC-U to different heavy metal ions when they coexisted in wastewater is also studied in this paper. The results show that the capture ability of DTC-U to Pb2+, Cd2+, Cu2+and Zn2+ions in wastewater following the sequence of Cu2+>Pb2+>Cd2+>Zn2+, and the residual concentration of the four kinds of heavy metal ions can meet the national discharge standards, the dosage of DTC-U is less than that when the four ions present alone separately in wastewater, while they can not achieve the same result when treated by alkali precipitation.(4) The capture ability to heavy metal ions of DTC-1and DTC-2synthesized by ethanediamine and triethylenetetramine respectively is compared with that of DTC-U in this paper. For neutral wastewater, DTC-U takes on better removal effect for Cd2+, while DTC-1and DTC-2have better removal for Cu2+and Pb2+respectively. Three of them are show better removal effect for the three kinds of ions than that of sodium sulfide. But for acid wastewater (pH<6) containing Cd2+, Pb2+and Cu2+, the removal effect of the three ions treated by DTC-U are better than that of DTC-1, DTC-2and sodium sulfide. Furthermore, the formation of hydrogen sulfide can be avoided when sodium sulfide used in acidic environment.In conclusion, DTC-U is synthesized with simple method. Its raw materials are low cost, less toxic and widely available. DTC-U also shows better treatment effect in treating various kinds of heavy metal wastewater at wide pH ranges. It can be dissolved in water easily and can not cause secondary pollution of hydrogen sulfide when used in acidic environment. It has great application foreground and market value prospects.