Abstract
Calligonum crinitum, a desert plant, was used as a natural adsorbent for the removal of Pb(II) ions from aqueous solutions. The sorption capacity of the sorbent was investigated through batch adsorption, as a function of contact time, metal ion concentration, and pH. The surface chemistry of the sorbent was probed using Fourier transform infrared spectroscopy, allowing an understanding of the key functionalities involved in binding the Pb(II) ions to the sorbent. Textural characteristics, including surface area and pore volume, showed higher surface areas relative to other natural adsorbents previously reported. Surface morphological analysis, observed via Scanning Electron Microscopy images and Energy-Dispersive X-Ray analysis, confirmed adsorption of Pb(II) ions, up to 71% on the surface of calligonum crinitum. Isothermal analysis, using Langmuir, Freundlich and Temkin models with nonlinear regression, showedthe Langmuir model to best represent adsorption within this system, yielding a maximum adsorption capacity of 337 mg g(-1) (pH 5.5, 30 degrees C). The optimum conditions of adsorption was pH, 5.5; adsorbent concentration, 0.3 g/l, contact time, 20 min at 30 degrees C. The Freundlich constant of < 10 indicates that adsorption of Pb(II) ions is favourable onto calligonum crinitum. Adsorption kinetics were modelled using pseudo-first-order, pseudo-second-order and intra-particle diffusion models; the results indicate that the kinetics are pseudo-second-order, suggesting a degree of chemical influence in the adsorption process. While thermodynamic analysis shows the process to be exothermic in nature with an ordering of solute within the adsorption process. Calligonum crinitum has, therefore, been proven as an effective sorbent for the removal of Pb(II) ions from aqueous solutions, with potential in water remediation processes.