Simultaneous adsorption of Pb(II) and Cd(II) in the presence of Mg(II) ion using eco-friendly immobilized dithizone on coal bottom ash

Simultaneous adsorption of Pb(II), Cd(II) and Mg(II) ions using activated coal bottom ash (Act-CBA) and dithizone-immobilized Act-CBA (Dtz-CBA) prepared in an eco-friendly medium of the alkaline solution has been done. The parameters affecting the adsorption, such as pH, contact time, initial concentration, and coexisting cations, were systematically investigated. The optimal adsorption was obtained at pH 5, 90 min of contact time and the adsorption of metal ions on both materials followed the pseudo-second-order kinetic model. Langmuir isotherm model fitted well the adsorption of Pb(II) and Cd(II) ions on both adsorbents. Significant increase in the maximum adsorption capacity (qmax) and Langmuir constant (KL) of both Pb(II) and Cd(II) ions on Dtz-CBA compared to that of Act-CBA indicated the stronger affinity of Dtz-CBA towards these two metal ions, while no significant change in capacity was observed for Mg(II) ions. In the binary solution of Pb(II) and other coexisting metal ions, the adsorption of Pb(II) on Dtz-CBA was not affected by Co(II), Ni(II), Zn(II), Ag(I), or Cd(II). However, mixing of all coexisting metal ions with Pb(II) ion in the solution resulted in the decrease in the adsorption of Pb(II) of about 65% compared to that of the single adsorption of Pb(II) ion, possibly due to the limited number of active sites in the solution. Results of sequential desorption suggested that metal ions interacted with Act-CBA mostly via electrostatic interaction and hydrogen bond, while for Dtz-CBA, the hydrogen bond and metal complexation increased significantly, especially for the interaction of Pb(II) and Cd(II) ions. Post-adsorption characterization of the adsorbents using SEM-EDX, FTIR, and XRD confirmed the adsorption of metal ions on the surface of materials, as indic