Calligonum Crinitum as a Novel Sorbent for Sorption of Pb(II) from Aqueous Solutions: Thermodynamics, Kinetics, and Isot
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ORIGINAL PAPER
Calligonum Crinitum as a Novel Sorbent for Sorption of Pb(II) from Aqueous Solutions: Thermodynamics, Kinetics, and Isotherms A. Safri1 · A. J. Fletcher1 · E. Abdel‑Halim2 · M. A. Ismail3 · A. Hashem2 Accepted: 12 November 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
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 °C). The optimum conditions of adsorption was pH, 5.5; adsorbent concentration, 0.3 g/l, contact time, 20 min at 30 °C. The Freundlich constant of Temkin > Freundlich. Langmuir model in providing the best overall fit for adsorption of Pb(II) onto calligonum crinitum (Fig. 7).Consequently, Langmuir analysis provides the best level of fit, and the value of maximum adsorption capacity was evaluated as 336.9 mg L−1 for Pb(II) ions onto the surface of calligonum crinitum. In addition, the Langmuir model is based on the assumption that the ions form a complete monolayer on the surface of the adsorbent, which suggests that the adsorption behaviour is influenced by homogenous character of the sorbent. The value of the Langmuir equilibrium constant KL (10.3 L g−1) shows a good affinity between the metal ions and the adsorbent. Meanwhile, the Freundlich model provides a reasonable level of fit (Table 1), therefore, the values determined from this fit can be additionally used to understand this system. The value of n (5.5) falls within the range 0–10, which indicates that the adsorption of Pb(II) ions onto calligonum crinitum is favourable, which is supported by the isotherms obtained. Calligonum crinitum adsorbent offers a high level of affinity for the removal of Pb(II) ions, as compared to other natural adsorbents previously reported [32].
Sorption Kinetics Further to studying the equilibrium adsorption behaviour for this system, it is essential to understand the sorption kinetics of the processes occurring, which gives an indication of the charging characteristics of the material, as well as providing insight into the mechanism of sorption. In the present work, th
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