Bioremoval and recovery of Cu(II) and Pb(II) from aqueous solution by a novel biosorbent watermelon (Citrullus lanatus) seed hulls: Kinetic study, equilibrium isotherm, SEM and FTIR analysis

The biosorption of Cu(II) and Pb(II) ions from aqueous solutions using a new sorbent, watermelon seed hulls (WSH), has been studied. The effect of pH (2–6), biosorbent dose (0.1–1.0 g), initial metal ion concentration (10–500 mg L−1), contact time (5–270 min), and temperature (293–333 K) was investigated. Equilibrium adsorption isotherms and kinetics were also investigated based on metals adsorption tests. The experimental data were analyzed by the Langmuir and Freundlich models of adsorption, and the results fitted well to the Langmuir isotherm. The kinetic data have been analyzed using pseudo-first-order, pseudo-second-order, and intraparticle diffusion equations. The experimental data fit very well with the pseudo-first-order kinetic model. The data obtained from adsorption isotherms at different temperatures were used to calculate some thermodynamic quantities, such as free energy (ΔGo), standard enthalpy (ΔHo), and standard entropy (ΔSo), were evaluated. The adsorption of these two metals on the WSH was found to be spontaneous and endothermic process in nature. Desorption experiments were carried out using various acid solutions with a view to regenerate the spent adsorbent and to recover the both adsorbed metal ions. According to the experimental results, WSH seems to be an effective, low-cost and alternative adsorbent precursor for the removal of Cu(II) and Pb(II) ions from aqueous solutions.