Novel Application of Tagua Shell (Phytelephas aequatorialis) as Adsorbent Material for the Removal of Pb(II) Ions: Kinetics, Equilibrium, and Thermodynamics of the Process

Tagua shell is a material generated in the handcrafted jewelry industry, which is discarded since it does not have a specific use. The present study evaluates this material as an adsorbent for the removal of lead (II) in aqueous media. The adsorbent was characterized through the point of zero charge technique, X-ray microanalysis, scanning electron microscopy, and Fourier-transform infrared spectroscopy. Tests were carried out in a static system using a lead (II) solution of 100 mg·L−1 to establish the process conditions, setting a pH of 5, an adsorbent dose of 1.8 g/100 mL, and a contact time of 60 min. The kinetic study performed showed that the experimental data had a better fit with the pseudo-second order model. The experimental equilibrium data were correlated using the Langmuir, Freundlich, Toth, Redlich–Peterson, and Sips models, of which the Langmuir and Sips models proved to be the best to represent the adsorption process due to the high coefficient of determination they presented at the different temperatures, being between 0.9629–0.9899 and 0.9819–0.9900, respectively. The maximum amount of lead adsorbed was 22.0348 mg·g−1 at a temperature of 298 K. Finally, the thermodynamics study indicated that the process is endothermic, spontaneous, and thermodynamically stable.