Kinetics and equilibrium isotherms of adsorption of Pb(II) and Cu(II) onto raw and arginine-modified montmorillonite

Arg-Mt, was fabricated by modifying sodium montmorillonite (Na-Mt) with Arginine monohydrochloride (Arg salt), to adsorb Pb(II) and Cu(II) in aqueous solution. The X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectrum, thermal analysis (TG/DTG), Brunauer-Emmett-Teller (BET) and Scanning electron microscope (SEM) were employed to investigate the properties of Na-Mt and Arg-Mt. The effects of the amount of modifier, pH value, the initial concentration of M(II), temperature and contact time were tested in a single adsorption system. The isotherm model was well matched with the Langmuir curve and the kinetic adsorption fitted well with the pseudo-second-order rate equation. The saturated adsorption of Pb(II) and Cu(II) by Arg-Mt were 124.69 and 29.15 mg/g, respectively, which were higher than that of Na-Mt (89.08 and 23.93 mg/g). The thermodynamic equation indicated that the adsorption process was spontaneous, endothermic, and the randomness of the samples changed a little after adsorption. The adsorption capacity of heavy metal ions in the binary co-adsorption system was poor than single adsorption system. Furthermore, the adsorbed M(II) onto Arg-Mt can hardly be dissolved under weak acidic condition (pH > 4) according to the desorption experiments. High-efficiency and low-cost make Arg-Mt to be used in the removal of heavy ions in aqueous solution.