Adsorption of heavy metals on activated carbons and their respective lignocellulosic precursors: experimental and theoretical approach

This work reports the application of lignocellulosic adsorbents and activated carbons prepared from vegetable residues in the removal of five heavy metals. The selected residues were: prickly pear peel, broccoli stem, white sapote seed, and agave fiber. The adsorption of heavy metals was studied individually, in mixture, and varying the pH of the aqueous solutions. For lead, individual adsorption rates of 3.07 and 6.67 mg/g (more than 97% removal) were reached using lignocellulosic adsorbents and activated carbons, respectively, at pH = 1. When found in mixture containing the five heavy metals, their individual adsorption rates decreased, but the global amount of metals adsorbed increased (9.98 mg/g). When pH = 2, the adsorption capacity of the activated carbons was increased twice. For the carbon produced with the agave fiber, it was 19.55 mg/g. This was the carbon with the largest adsorption capacity for heavy metals. The best lignocellulosic adsorbent to remove the heavy metals was that prepared from broccoli stem. Considering that carbonaceous materials contain layers of graphene in their structure, the interaction between metallic nanoparticles was modeled on a graphene surface using the software DMo13, and the order of adsorption of heavy metals on activated carbons nearly agreed with the adsorption energies predicted by the theoretical modeling.