Development Of Polyethyleneimine-loaded Nanocomposites For Enhanced Removal Of Heavy Metals From Water

Polyethyleneimine (PEI) is an attractive chelating reagent for heavy metals, but its application in water treatment is greatly limited by its good solubility. In this thesis a novel nanocomposite adsorbent of high preference toward toxic metal removal was fabricated by loading soluble PEI firmly onto a macropore polystyrene cation exchange resin.PEI was loaded onto the exchanger D001 through a simple wetting technique. The as-obtained nanocomposite D001-PEI was well characterized by elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), scanning electronic microscopy (SEM), transmission electron microscope (TEM), pore and specific area (BET), thermogravimetric analysis (TGA), and pH titration. PEI nano-clusters were uniformly dispersed into the outer and inner phase of D001. D001-PEI had good mechanical strength and thermal stability. Negligible PEI loss was observed when D001-PEI was immersed into solution of pH< 10.5 and/or ionic strength< 0.5 mol/L (NaCl). Also, it could be employed for long-term use in weakly basic solution such as NaHCO3, CH3COONa and NH3.H2O. The stability of D001-PEI may be due to the strong electrostatic interaction between polyamine cation and sulfonic groups; Spatial confinement and encapsulation by the resin matrix could be possible reasons as well.The use of D001-PEI for heavy metal removal (particularly for copper ions) was investigated as a function of solution pH, time, and diverse coexisting cations. In the studied pH ranges (1-6) increasing solution pH was favorable for Cu(Ⅱ) retention by D001-PEI. Compared to the host D001, D001-PEI displays more preferable Cu(II) retention in the presence of competing Mg2+, Ca2+and Sr2+ at greater levels in solution. The adsorption of Cu(II) onto D001-PEI fitted the Langmuir isotherm with the maximum capacity 99 mg/g. The pseudo-second-order kinetic model could represent the kinetic date well. Fixed-bed adsorption runs showed that Cu(II) sequestration on D001-PEI could result in its conspicuous decrease from 5 mg/L to below 0.01 mg/L with the treatment volume of 480 BV (Bed Volume). The spent hybrid adsorbent can be readily regenerated by 8-10 BV of 0.2 mol/L HCl+0.5 mol/L NaCl binary solution for repeated use. The coexisting anions (SO42-, Cl-,NO3-) and humic acid (HA) in water imposed negligible adverse effect on the Cu(II) adsorption onto D001-PEI. Also, the as-obtained composite could be used to effectively remove other toxic metals including Ni(Ⅱ), Zn(Ⅱ), Cd(Ⅱ) and Pb(Ⅱ).Furthermore, we fabricated another nanocomposite D001-PEI-GA through PEI self-crosslinking by glutaraldehyde upon Cu(Ⅱ)-template process. As expected, D001-PEI-GA presented better chemical stability and higher adsorption capacity than D001-PEI. Elemental alalysis, SEM, TEM and BET was employed to characterize the resultant composite. The crosslinked-PEI nanoclusters were dispersed uniformly within the D001 and firmly immobilized even in solution of pH 13 or 1 mol/L NaCl. This is mainly because the self-crosslinked PEI was insoluble in water. Cu(Ⅱ) adsorption onto D001-PEI-GA followed pseudo-second-order kinetic model well. Compared to D001, D001-PEI-GA displayed more preferable Cu(Ⅱ) sequestration in the presence of co-ions Mg2+, Ca2+ and Sr2+ at higher levels. Fixed-bed adsorption showed that Cu(Ⅱ) sequestration on D001-PEI-GA could result in its conspicuous decrease from 5 mg/L to below 0.01 mg/L with the treatment volume as high as 630 BV per run. Also, the spent composite adsorbent can be readily desorbed by 12-14 BV 0.3 mol/L HC1+0.5 mol/L NaCl binary solution and regenerated with 3 BV 0.5 mol/L NaHCO3 for repeated use.Finally, D001-PEI was fabricated in pilot scale and employed to remove Cu(Ⅱ) and Ni(II) from an electroplating effluent. Prior to D001-PEI adsorption, the effluent was subjected to NaClO oxidation to lower COD values and to minimize the effect of organic pollutants on subsequent metal removal. D001-PEI adsorption in column mode could eliminate both toxic metals from several mg/L to below 0.02 (Cu2+) and 0.01 (Ni2+) mg/L respectively. Also, the spent D001-PEI could be employed for multiple uses after regeneration. The pilot tests achieved satisfactory results as expected.