Kinetics and thermodynamics of Cr(VI) ion adsorption onto organo-bentonite from the Amazon region

A natural bentonite clay sample from the Amazon region (Amazonas State) was utilized for the synthesis of new hybrid materials (organo-bentonite) produced by the organofunctionalization process. The organo-bentonite types were composed of an Amazon bentonite sample, 3-aminopropyltrietoxisilane and 3,2-aminoethylaminopropyltrimetoxisilane. The natural bentonite and organo-bentonite samples were used in batch studies for the adsorption of Cr(VI) ions from aqueous solution. The adsorption data were fitted to equilibrium and kinetic models. The effects of stirring time, adsorbent dosage and pH on the adsorption capacity demonstrated that 90 min is sufficient to reach equilibrium at room temperature and over a pH range of 6.0-8.0, the batch results were confirmed by column method and show that the adsorption process of materials accorded with Redlich-Peterson, Sips, and Langmuir isotherm models. The exothermic enthalpic values reflected a favorable energetic process for chromium ions anchored in the material surfaces. The negative Gibbs free energy results supported the spontaneity of three adsorption reactions with Cr(VI) ions. The model of Adams-Bohart was used to analyze the adsorption experimental data and the model parameters were evaluated.