Newly Synthesis, Structural Characterization, Selective Adsorption Properties And Inside Mechanisms For Heavy Metal Ions Of Dual-amine Chelating Resins

The toxic heavy metals, such as copper, lead and nickel, usually coexist in the wastewater of electronic electroplating, mining and refining which pose great threats to environmental safety and public health. More attention have been paid on pollution control especially for heavy metals recently in China. However, the traditional precipitation and extraction methods always cause secondary pollution, while the conventional ion exchange and adsorption techinques lack of salt tolerance and selectivity. So, new adsorbents and techniques suitable for treating wastewater containing both heavy metals and salt become a top research subject. Herein, series of dual-amine chelating resins were synthesized to investigate the adsorption behavior for heavy metal ions from single and binary aqueous systems. Further, the enhancement removal upon heavy metals with the coexistence of mineral salt told the new resin and technology could be succeeded in removing and reusing heavy metals especially from saline wastewaters.To get series of dual-amine chelating resins (EDAA、EDTB、EDTC), polyamine was introduced to chloromethylation crosslinking polystyrene with the help of dimethyl 5-aminoisophthalate. Characterization of resins involving PSD, SEM, EA, FTIR and XPS, proved all the resins could be prepared with much success. The nitrogen content of the resins was 11.24%～12.62%, and the functional group was in the range of 1.001～1.605 mmol/g.The adsorption isotherms of Cu(II), Pb(II) and Ni(II) could be all described by Langmuir model, and the calculated equilibrium capacity was in the order of Pb(II)>Cu(II)>Ni(II) in the single system. EDTB owned the largest adsorption capacity for Cu(II), Pb(II), Ni(II), as 2.073 mmol/g,2.118 mmol/g and 0.589 mmol/g respectively at the optimum pH value of 3-4. The adsorption processes were endothermic and spontaneous impelled by entropy. The kinetic data could be well fitted by Lagergren-second-order equation. The adsorption rate followed the order of Cu(Ⅱ)>Pb(Ⅱ)>Ni(Ⅱ) which was in relevance with the first hydrolysis constants of metal ions. In dynamic adsorption, the effluent volume between breakthrough point and end point was 182 BV and 615 BV for Cu(II) and Ni(II), while the half adsorption time was 70.8 h and 10.0 h, respectively. Significant difference in the dynamic curves suggested an efficient separation in coexistent systems. Moreover, the resin could be thorough regenerated by 15% HC1 and reused with stable adsorption properties. The FTIR and XPS spectra before and after interatcion with metals demonstrated that the nitrogen was associated with the coordination while the oxygen did not participate in the processes.The binary adsorption isotherms were studied for different systems and could be well fitted to the Extended Langmuir model. The seperation factor of Cu(II) versus Ni(II) was largest among all systems. Compared to the single system, the adsorption of preferential ion Cu(II) was enhanced while the other disadvantage ion Ni(II) was reduced. This was mainly due to the enhancement effect of anions for the former case and the direct competitive effect of coexistent metal ions for the latter case. In the separation of equal mole Cu(II) and Ni(II) simulated wastewater, about 70 BV pure nickel solution coule be obtained.Obviously, the equilibrium capacity for the preferential Cu(II) increased by 85.10% and 146.10% while the capacity for the disadvantage Ni(II) decreased by 17.74% and 57.52%, in comparison with the single, binary and saline systems. In 1600mmol/L sodium nitrate solution, the adsorption capacity of EDTB for Cu(II) was up to 0.873 mmol/g, about 1.56,1.02,291 times the capacity of those commercial ion change and chelating resins such as Amberlite747, Amberlite748 and D001. The selective coefficient of Cu(II) versus Ni(II) tended to infinity in the saline system. The above mentioned phenomena testified the practical application in seperating Cu(II) and Ni(II).Furthermore, the inside mechanisms in super adsorption and successful seperation was deeply illuminated. Nitrogen coordination was proved to be dominant between resin and heavy metal ions. Meanwhile, anions could enhance the adsorption processes through maintaining the electroneutrality of solid phase. The adsorption and separation properties were comprehensive effect of enhancement effect from anions and competitive effect from metal ions.Consequently, EDTB resin was proved an efficient and salt-tolerance functional material with stable adsorption and seperation properties. With expected, the novel resin could provide a new method to remove and recover heavy metal ions from saline wastestreams.