Synthesis And Application Of A Water-soluble Thiourea-formaldehyde(WTF) Heavy Metal Chelating Agent

Heavy metal pollution is a serious problem in our country which has been a threat to the human's health.Among the commonly used methods to treat heavy metal pollution,solidification/stabilization technology by using chemical agent has its advantage on the short treatment cycle and the low cost.The polymer with thiourea as the function group has a great ability of adsorbing heavy metal ions.The chelating agents with thiourea function group were prepared a macromolecule organic polymer,which are insoluble in water.They only can be used to treat the heavy metal pollution in water.So,synthesis a new water-soluble heavy metal chelating agent with thiourea function group might have a bright future.A novel water-soluble thiourea-formaldehyde(WTF)heavy metal chelating agent was synthesized by two step reactions(hydroxymethylation reaction and condensation reaction).Synthetic conditions,the ability of immobilization heavy metals in water and MSWI fly ash and the removal of free formaldehyde in the WTF heavy metal chelating agent were studied in this paper.The possible molecular structure of the resin was also discussed by elemental analysis and FTIR spectra.The experimental results showed that the synthesis conditions of the WTF heavy metal chelating agent were the formaldehyde/thiourea mole ratio of 2.5:1,and the melamine/thiourea mole ratio of 0.02:1.Hydroxymethylation at pH=4.5-8.0 and 30 min,and condensation at pH=4.5-5.0 and 80?.In addition,the end point of condensation reaction was measured by turbidity point method.And when the addition amount of melamine is 7% to the weight of the chelating agent,the concentration of the free formaldehyde is decline from 8.5% to 2%.The experimental results showed that when the addition amount of WTF heavy metal chelating agent is 2% to the weight of wastewater,the concentrate of Cd ions decline from 10mg/L to 1mg/L,lower than the national standard limit.When the addition amount of WTF heavy metal chelating agent is 3% to the weight of the MSWI fly ash,the toxic leaching test showed that the immobilization rates of Cr,Pb and Cd were 96.5%,92.0% and 85.8%.Leaching concentrations of Cr,Pb and Cd in the treated fly ash were decreased to 0.08 mg/L,2.44 mg/L and 0.23 mg/L,respectively.The leaching toxicity of heavy metals is lower than the national standard limit.