BIOSORPTION OF LEAD (II) IN AQUEOUS SOLUTION ONTO RESIDUES OF NATURAL FIBERS FROM THE IXTLE INDUSTRY (Agave lechuguilla Torr. AND Yucca carnerosana (Trel.) MCKELVEY)

Lead has been recognized as one of the most toxic metals due to its negative effect on the environment. In the present work, the potential use of Agave lechuguilla Torr. lechuguilla) and Yucca carnerosana (Trel.) McKelvey (yucca) residues from the ixtle industry to remove Pb (II) ions in an aqueous solution was evaluated. The adsorption equilibrium data showed that when increasing the pH in the solution from 2.0 to 5.0, the biosorption capacity of both materials increases. This effect might be explained by the negative surface charge of these materials, which is greater at high pH, favoring the removal of Pb (II). The effect of the temperature of the solution on the biosorption isotherms revealed the endothermic nature of the biosorption process. The Gibbs free energy change and the calculated entropy (Delta G degrees and Delta S degrees) indicated the spontaneity of biosorption and the affinity of Pb (II) in the solution for biosorbents, respectively. The variation of the biosorption capacities of lechuguilla and yucca was attributed to the different content of acid sites and lignin, which resulted in the presence of different biosorption mechanisms. In both materials, the biosorption of Pb (II) occurs by pi-cation interactions, electrostatic attractions and ion exchange; moreover, a microprecipitation process on lechuguilla was evinced.