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) AlCl3.6H2O/NaOH, (ii) titanium ethoxide in hydrochloric acid and (iii) direct use of ZrOCl2.8H2O 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 (A1) from 1.55 to 2.06 nm and the surface area from 44.30 to 223.73 m2 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 K2=4.17-10.43 x 10(-3)g mg(-1)min(-1) for the A1 sample.