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Ziziphus spina-christi L. (ZscL) is a plant residue that has been used as adsorbent for the removal of Hg(II) ions from an aqueous solution. The ability of ZscL to adsorb Hg(II) ions was investigated by using the batch adsorption procedure. It was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) to support the adsorption of Hg(II) ions. The effects of various parameters on the adsorption process, such as contact time, adsorbent concentration, solution pH and initial concentrations of metal ions were studied to optimize the conditions for maximum adsorption. Experimental equilibrium data were fitted to the Freundlich, Langmuir, Dubinin-Radushkevich, Halsey and Temkin (two parameter models), Redlich-Peterson, Sips, Khan, Hill, Radke-Prausnitz, Langmuir-Freundlich and Toth (three parameter models), Fritz-Schlunder and Baudu (four parameter models) and Fritz-Schlunder (five parameter model) at 30°C by using nonlinear regression analysis. The examination of error analysis methods showed that the Halsey model provides the best fit for experimental data compared with the other isotherms. Various kinetic models have been applied to the experimental data to predict the adsorption kinetics. It was found that pseudo-second-order rate was better obeyed than pseudo-first-order reaction, supporting that the chemisorption process was involved. The obtained results show that ZscL can be used as an effective and natural low-cost adsorbent for the removal of Hg(II) ions from aqueous solutions.

Retama raetam (RR), a desert plant, was chemically modified by the reaction with succinic acid at high temperature to form succinic acid treated R. raetam (STRR). Three levels containing different carboxyl contents of STRR were prepared. Native RR and STRR were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and estimation of carboxyl content to support the adsorption of Pb(II) ions. The STRR adsorbent was utilized as adsorbent material for the removal of Pb(II) ions from aqueous solutions. The effect of various parameters like pH, adsorbent concentration, contact time, temperature and initial concentration was investigated using batch process to optimize conditions for maximum adsorption. The adsorbent data were analyzed using two-, three-, four- and five-parameter models at 30°C by non-linear regression analysis. The examination of error analysis methods showed that the Langmuir-Freundlich model provides the best fit for experimental data compared with other isotherms. The maximum biosorption capacity of Pb(II) ions was up to 270.27 mg/g at 30°C. The thermodynamics constants of the adsorption process, viz., ΔHo, ΔGo and ΔSo, were evaluated. The results showed that the adsorption of Pb(II) ions onto STRR was endothermic and spontaneous. The adsorption data followed second-order kinetics, supporting that chemisorption process was involved.

In the present study, we reported the feasibility of the Sesbania sesban L. as a biosorbent to remove Pb(II) from aqueous solutions. The ability of S. sesban L. to adsorb Pb(II) was investigated by using batch adsorption procedure. Such effects as pH, contact time, adsorbate concentration, and biosorbent dosage on the adsorption capacity were studied. The experimental data were analyzed using various adsorption kinetic models, namely, pseudo-first-order model, the pseudo-second-order model, Batacharia-Venkobachar, the Elovich equation, the intraparticle diffusion model, and Bangham equation. Results show that the pseudo-second-order equation provides the best correlation for the biosorption process. To determine the best fit isotherm, the experimental equilibrium data were analyzed using two-parameter (Langmuir, Freundlich, Dubinin-Radushkevich, and Tempkin) and three-parameter isotherms (Redlich-Peterson, Sips, Khan, and Toth). The examination of error analysis methods showed that the Langmuir isotherm model and Redlich-Peterson models provide the best fit for experimental data than other isotherms. Sebania sesban L. is found to be inexpensive and effective adsorbent for removal of Pb(II) from aqueous solutions.