Adsorptive, thermodynamic and kinetic performances of Al/Ti and Al/Zr-pillared clays from the Brazilian Amazon region for zinc cation removal

Smectite clay samples from the Amazon region, Brazil, were pillarized by intercalating the species obtained from the chemical reactions: (i) AlCl3 center dot 6H(2)O/NaOH, (ii) titanium ethoxide in hydrochloric acid and (iii) direct use of ZrOCl2 center dot 8H(2)O solution. The natural matrices and the pillaring solutions were maintained under vigorous stirring at 298 K for 3 h and then subjected to calcination at temperatures of 723 and 873 K. Natural and pillared matrices were characterized by XRD, FTIR, TG-DTG and nitrogen adsorption-desorption isotherms. The resulting materials were used for zinc adsorption from aqueous solution at room temperature. The Langmuir, Freundlich and Temkin adsorption isotherm models have been applied to fit the experimental data and the Freundlich model is limited for higher concentrations. The pillaring process increases the thermal stability, the basal spacing of the natural clay sample (A(1)) from 1.55 to 2.06 nm and the surface area from 44.30 to 223.73 m(2) g(-1). Kinetic studies demonstrated an equilibrium time of 180 min for zinc adsorption on the pillared matrices. Pseudo-first-order, Lagergren pseudo-second-order and Elovich equations demonstrated a better agreement with second-order kinetics was obtained with K-2 = 4.17-10.43 x 10(-3) g mg(-1) min(-1) for the A(1) sample. (C) 2007 Elsevier B.V. All rights reserved.