Application as absorbents of natural and functionalized Brazilian bentonite in Pb2+ adsorption: Equilibrium, kinetic, pH, and thermodynamic effects

The capacities of natural and modified Brazilian bentonite samples as adsorbents to remove lead were investigated under several conditions in batch and column methods. The raw material, natural bentonite, was modified by anchorament of 3-aminopropyltrietoxisilane (APS) and 3,2-aminoethylaminopropyltrimetoxisilane (AEAPS) in the surface of component minerals of bentonite sample. Adsorption behavior of three bentonite types was strongly depending on pH of adsorbate solution, contact time adsorbent/adsorbate, and initial concentration of metal. The maximum adsorption capacities of bentonite types were 20.6843, 27.6524, and 29.5413 mg g−1 for natural, bentonite functionalized by APS, and bentonite functionalized by AEAPS, respectively. The results were confirmed by column method and show that the adsorption process of materials accorded with Sips and Langmuir isotherm models. The pseudo-second-order model simulation was also introduced to reveal the principles of the lead removal. The exothermic enthalpic values reflected a favorable energetic process for lead atoms anchored in the material surfaces. The original and modified bentonite samples were characterized by elemental analysis, scanning electron microscopy, and X-ray diffraction powder. The negative Gibbs free energy results supported the spontaneity of three adsorption reactions with Pb2+.