Kinetic and thermodynamic studies of adsorption of lead (ii) ions on magnetite, baobab (<i>Adansonia digitate</i>) and magnetite - baobab composite

Abstract

The detrimental consequences of excessive levels of heavy metal contamination on living things served as the motivation for this study. Adsorption of Pb(II) ions was investigated on synthetic magnetite (MG), baobab fruit shell (BB) and magnetite-baobab composite (MB). The batch equilibrium technique was used to investigate the adsorption of Pb(II) ions. The effects of initial metal concentrations (15-500 mg/L), adsorbent dose (0.05-0.3 g), contact time (5-150 min), pH (2-8) and temperature (303-343 K) on the adsorption capacity of the adsorbent were studied. Langmuir, Freundlich and Temkin isotherms were used to describe the adsorption of Pb(II) ions. The maximum adsorption capacity, qmax, of MB, MG and BB was 249.86, 227.45 and 34.67 mg/g respectively at a concentration of 500 mg/L of Pb(II) ions. Freundlich model was shown to have the best fit for the adsorption data in the following order: BB > MG > MB, with R2 values of 0.9954, 0.980 and 0.9797 respectively. Freundlich adsorption intensity for MG, BB and MB are 1.590, 1.339 and 1.761 respectively. The kinetic and thermodynamic investigations revealed that the adsorption followed pseudo-second-order kinetics and endothermic process. The amount of Pb(II) ions adsorbed after each stage of the desorption process varied between the different acid concentrations, according to sorption-desorption studies using spent adsorbents. The highest stepwise adsorptions of Pb(II) ions were observed when 0.5 M HCl was utilized as a stripping agent for BB while 0.1 M HCl favoured MG and MB.