Sorption of Hg(II) and Zn(II) Ions using Lignocellulosic Sorbent (Date Pits)

This work focuses on the study of Hg(II) and Zn(II) sorption using pristine date pits. The effect of pH is evaluated before considering the influence of both temperature and contact time on sorption efficiency. Sorption isotherms are also determined and modelled using conventional models such as Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) equations. The best fit was obtained with the Langmuir equation and maximum sorption capacities reached 38.5 and 52.6 mg.g(-1), for Hg(II) and Zn(II), respectively. An analysis of the temperature effect by the Gibbs equation showed that the sorption is exothermic and spontaneous. The mean free energy of sorption (obtained from D-R equation) confirms that metal binding occurs through a chemical ion-exchange mechanism. The kinetic profiles can be accurately fitted with the pseudo-second order rate equation. Complementary analyses (using FTIR spectrometry and SEM-EDX analysis) confirm that ion-exchange is the main binding mechanism, though a contribution of surface complexation cannot be neglected.