Adsorption and Removal of Cr(6+), Cu(2+), Pb(2+), and Zn(2+) from Aqueous Solution by Magnetic Nano-Chitosan

Magnetic nano-chitosan (MNC) was prepared and characterized. The kinetics, thermodynamics, and influencing factors of the adsorption of Cr(6+), Cu(2+), Pb(2+), and Zn(2+), as well as their competitive adsorption onto MNC in aqueous solution, were studied. The results showed that the adsorption kinetics and thermodynamics of Cr(6+), Cu(2+), Pb(2+), and Zn(2+) were well described by the pseudo-second-order kinetic model and Langmuir isothermal adsorption model, indicating that the adsorption was mainly chemical adsorption and endothermic. Increasing the dosage of MNC, the equilibrium adsorption capacity (q(e)) of Cr(6+), Cu(2+), Pb(2+), and Zn(2+) decreased; their removal rate (η) increased. With the increase in the solution’s pH, the q(e) and η of Cr(6+) first increased and then decreased; the q(e) and η of Cu(2+), Pb(2+), and Zn(2+) increased. With the increase in the metal ion initial concentration, the q(e) increased; the η of Cr(6+), Cu(2+), and Zn(2+) decreased, while the η of Pb(2+) increased first and then decreased. Temperature had a weak influence on the q(e) of Cr(6+) and Pb(2+), while it had a strong influence on Cu(2+) and Zn(2+), the q(e) and η were greater when the temperature was higher, and the adsorption was spontaneous and endothermic. The q(e) and η of Cu(2+), Pb(2+), and Zn(2+) decreased in the presence of co-existing ions. The influences among metal ions existed in a binary and ternary ion system. The current study’s results provide a theoretical support for the simultaneous treatment of harmful metal ions in wastewater by MNC.