Chemically modified Retama raetam biomass as a new adsorbent for Pb(II) ions from aqueous solution: non-linear regression, kinetics and thermodynamics

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 degrees 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 degrees C. The thermodynamics constants of the adsorption process, viz.,Delta H degrees,Delta G degrees and Delta S degrees, 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.