Sorption of Ni(II) by Fe(II) and EDTA-modified activated carbon derived from pyrophosphoric acid activation

Activated carbon (LSAC) was obtained from lotus stalk by pyrophosphoric acid activation. The LSAC was modified by FeCl2 and Na2EDTA (Fe–EDTA/LSAC) to enhance its ability for Ni(II) sorption from aqueous solutions. The activated carbons were characterized by N2 adsorption and desorption isotherms, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction. The sorption of Ni(II) from aqueous solution onto the LSAC and Fe-EDTA/LSAC under various conditions of dosage, contact time, initial solution pH, initial Ni(II) concentration, and ionic strength was investigated to illustrate the mechanism and to quantify the sorption parameters. LSAC and Fe-EDTA/LSAC were mainly microporous with pores almost less than 4 nm. Although the surface area of LSAC (824 m2 g−1) was much higher than that of Fe–EDTA/LSAC (445 m2/g), the Ni(II) sorption capacity of Fe–EDTA/LSAC was larger than that of LSAC. The pH and ionic strength studies indicated that the main Ni(II) sorption mechanisms by the carbons were electrostatic attraction and cation exchange. The kinetics and equilibrium data agreed well with the pseudo-second-order kinetics model and Langmuir isotherm model.