Competitive sorption of Cd2+ and Pb2+ from a binary aqueous solution by poly (methyl methacrylate)-grafted montmorillonite clay nanocomposite

Abstract

Poly(methyl methacrylate)-grafted montmorillonite (PMMAgMMT) clay and sodium-exchanged montmorillonite (NaMMT) clay were prepared through in situ graft polymerisation and used to remove Cd2+ and Pb2+ from synthetic wastewater. The modification of adsorbent materials was confirmed by fourier transform infra-red spectroscopy (FTIR), thermogravimetric analysis (TGA) and X-ray powder diffraction (XRD) techniques. BET surface area measurements showed NaMMT had a higher surface area than PMMAgMMT. Batch experiments were used to assess the simultaneous uptake of Cd2+ and Pb2+ from a synthetic binary solution. Pb2+ was preferentially sorbed, exhibiting greater affinity for the sorbents compared to Cd2+ as shown by its relatively higher uptake onto the sorbents than Cd2+. The maximum sorption capacities for NaMMT and PMMAgMMT were 18.73 and 19.27 mg/g for Cd2+, and 30.03 and 34.25 mg/g for Pb2+, respectively. The sorption data obeyed the Langmuir model and the pseudo-second order kinetic model with R2 of at least 0.9800 for both models. The sorbents could also be regenerated up to three cycles without a significant loss in the sorption capacity. FTIR measurements showed the presence of metal–oxygen bonds after sorption, confirming the occurrence of adsorption as one of the heavy metal removal processes. The work demonstrated the potential of using low-cost nanoscale composite material for the removal of Cd2+ and Pb2+ from aqueous solution.