Application of strongly basic anion exchangers for removal of heavy metal ions in the presence of green chelating agent

Sorption properties of strongly basic polystyrene and polyacrylate anion exchangers towards Cu(II), Zn(II), Cd(II) and Pb(II) in the presence of the green chelating agent of a new generation ethylenediamine-N,N′-disuccinic acid (EDDS) were investigated in the batch and column systems. Batch sorption experiments were performed using commercial forms of Amberlite IRA 402, Lewatit MonoPlus MP 500, Amberlite IRA 458 and Amberlite IRA 958. The amount of resin, e.g. the anion exchanger dose (0.1–1.0 g), the initial solution pH (2–12), the initial concentration of sorbed complexes in the M(II)–EDDS = 1:1 system (2 × 10−3 to 1.5 × 10−2 M), temperature (293–333 K) as well as the contact time (1–120 min) were changed. The sorption capacities of these anion exchangers increased with the increasing initial solution pH, temperature and concentration of complexes. Levels of sorption rapidly approached an equilibrium state within 20–30 min. The equilibrium data of the experiments show that Amberlite IRA 402 and Lewatit MonoPlus MP 500 are good anion exchangers for the removal of EDDS complexes. The sorption characteristics of metal complexes with EDDS onto these anion exchangers were based on the Langmuir and Freundlich isotherms. However, the values of correlation coefficients (R2) higher than 0.99 show that in the studied concentration range the data were more suitable for the Langmuir model. The maximum sorption capacities (q0) were 104.17, 62.11, 119.54, 134.93 mg/g for Cu(II), Zn(II), Cd(II) and Pb(II) complexes with EDDS on Amberlite IRA 402, respectively. For Lewatit MonoPlus MP 500 the obtained values were almost analogous. The values of calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) indicate that the sorption process is endothermic and spontaneous. The sorption kinetic of studied anion exchangers fitted well to the pseudo second-order model. These data were also evaluated based on the Boyd equation. Furthermore, the anion exchangers were characterized by Fourier transform infrared (FT-IR) and scanning electron microscope (SEM).