Carbon‐Coated Magnetic Fly Ash Modified with Guanylthiourea and Polydopamine for Simultaneous Removal of Cu(II) and Pb(II) in Acidic Aqueous Solutions

Abstract A magnetic adsorbent simultaneously adsorbing heavy metal ions in acidic solution was prepared by carbon‐deposited magnetic fly ash (C‐MFA), polydopamine (PDA) coating, and guanylthiourea grafting. The prepared guanylthiourea‐grafted PDA/carbon‐coated magnetic fly ash beads (GPC‐MFA) were characterized by SEM, FTIR, Raman spectroscopy, XRD, XPS, TG‐DSC, surface potential, and vibrating‐sample magnetometry. The results indicated that dopamine‐coated carbon‐deposited fly ash surface was successfully grafted with guanylthiourea. The maximum adsorption capacity fitted by Langmuir model for GPC‐MFA were 50.09 mg/g for Cu(II) and 30.64 mg/g for Pb(II) at 40 °C and pH 3.0, respectively. The pseudo‐second order kinetic model accurately fits the kinetic data of Cu(II) adsorption, hence the adsorption properties mainly involves chemical adsorption. Mechanistic studies show that GPC‐MFA contains uniform groups and has strong coordination with heavy metal ions. GPC‐MFA exhibited high recyclability. After 5 recycles of adsorption‐desorption, the adsorption capacity of GPC‐MFA for Cu(II) and Pb(II) still reached 88.72 % and 86.21 % compared with the fresh adsorbent.