Adsorption of Cu–EDTA complexes from aqueous solutions by polymeric Fe/Zr pillared montmorillonite: Behaviors and mechanisms Original Research Article

In this study, poly-hydroxyl iron/zirconium pillared montmorillonites have been utilized as adsorbents for the removal of Cu–EDTA chelates from aqueous solutions. Batch experiments were conducted to examine the effects of solution pH, initial concentration, contact time, temperature, ionic strength and coexisting ions on the Cu–EDTA removal. The results demonstrated that the uptake of Cu–EDTA on the pillared montmorillonites maintained high-efficiency in the pH range of 3.0–9.0. The adsorption data was found to fit well the Freundlich isotherm equation with R2 above 0.99 and followed the Pseudo-second-order model with a short equilibrium time of 30 min. The Cu–EDTA removal decreased slightly as temperature increased from 25 °C to 45 °C and ionic strength varied from 0.001 M to 0.05 M. The presence of phosphate and tartaric significantly reduced the adsorption of Cu–EDTA and the effects of the coexisting ions followed the order: C4H4O62− > PO43− > SO42− > CH3(CH2)11SO3− > NO3−. Furthermore, Electron paramagnetic resonance (EPR) results revealed different adsorption mechanisms involved in acidic and basic solutions. The spectroscopy data together with the macroscopic adsorption results suggested that the adsorption process of Cu–EDTA on pillared montmorillonites involved electrostatic interaction and also an inner-sphere complexation which could include several complexation patterns.