Adsorption studies of zinc(II) on magnetite, baobab (Adansonia digitata) and magnetite–baobab composite

The negative effect of high concentration of heavy metals in the environment on living species prompted this research. A study of adsorption of zinc on synthesized magnetite (MG), baobab fruit shell (BB) and magnetite–baobab composite (MB) was carried out. The adsorption of Zn(II) ions was examined using batch equilibrium technique. The effects of initial metal ions concentrations (15–150 mg/L for zinc), adsorbent dose (0.05–0.3 g), contact time (5–150 min), pH (2–8) and temperature (303–343 K) on the sorption capacity of these adsorbents were investigated. The Zn(II) ions at a solution concentration of 150 mg/g gave maximum adsorption capacity of 38.25, 33.95 and 29.20 mg/g for MB, MG and BB, respectively. The adsorption of Zn(II) metal ions was modelled using Langmuir, Freundlich and Temkin isotherms. The highest correlation coefficient (R2) value was obtained from Freundlich model for Zn(II) adsorption on MG and MB as 0.986 and 0.973, respectively, while that of Zn(II) on BB was obtained from Langmuir model as 0.993. The kinetic and thermodynamic studies revealed that the adsorption processes followed pseudo-second-order kinetics and were endothermic in nature. Desorption experiments were conducted on the spent adsorbent using 0.1, 0.2, 0.5, 1.0 and 2.0 M HCl to determine the reusability potentials of the adsorbents. There was an decrease in the amount of Zn(II) ions adsorbed after each stage of desorption process varied between the different acid concentrations. The 0.1 M HCl gave the highest degree of adsorption for Zn(II) on BB, while 0.2 M HCl was the best for MG and MB.