Adsorption of Cu(II), Ni(II) and Zn(II) on dye loaded groundnut shells and sawdust

The potential of cheap cellulose-containing natural materials like groundnut shells and sawdust was assessed for Cu(II), Ni(II) and Zn(II) adsorption from their aqueous solutions. These materials showed good adsorption capacities, although the levels differed depending on the combination of adsorbing material and metal ion. Application of a specific dye, C.I. Reactive Orange 13 onto the material further enhanced the adsorption capacity. The maximum metal ion uptake values for Cu(II), Ni(II) and Zn(II) were 7.60, 7.49 and 9.57 mg/g, respectively, for the dye loaded groundnut shells as against the respective values 4.46, 3.83 and 7.62 mg/g achieved when the unloaded groundnut shells was used as adsorbent. Similarly, the dye loaded sawdust gave the adsorption values 8.07 mg/g for Cu(II), 9.87 mg/g for NI(II) and 17.09 mg/g for Zn(II), which were higher than the corresponding values 4.94, 8.05 and 10.96 mg/g achieved with unloaded sawdust as adsorbent. With lowering of the pH of a metal ion solution, all the adsorbing materials showed a decrease in the adsorption capacities. When the pH of a metal cation solution was decreased to the lowest level at 1.5, the adsorption reached to very low values in all the cases. Even under low pH, the adsorption of metal ions on dye-loaded adsorbents was comparatively higher. This was made use of in desorption studies. Adsorption isotherm models were developed wherein the best fit was obtained in the Langmuir model. The regeneration and reusability of the adsorbents were also assessed for three successive adsorption–desorption cycles and were found to retain the adsorptive capacity.