Competitive adsorption of malachite green and Pb ions on natural zeolite.

A natural zeolite was employed as adsorbent for removal of malachite green and Pb(2+) ions from aqueous solution. A batch system was applied to study the adsorption behaviour of the dye and heavy metal in single and binary systems on the natural zeolite. Kinetic studies indicate that malachite green and Pb(2+) adsorption on the natural zeolite in a single component system follows the first-order kinetics and the adsorption is diffusion process with single-stage for Pb(2+) and two-stage for malachite green. For the single system, malachite green adsorption isotherm follows the Langmuir model while Pb adsorption follows the Freundlich isotherm. The adsorption capacities of malachite green and Pb at 30 degrees C, pH 6 are 5x10(-5) and 10x10(-5)mol/g, respectively. In the binary system, malachite green and Pb(2+) exhibit competitive adsorption on the natural zeolite. The adsorption is reduced to 90 and 80% of single component of Pb(2+) and malachite green, respectively. However, the total adsorption is higher. In the binary system, Pb(2+) exhibits relative higher affinity and selectivity to be adsorbed on zeolite. The dynamic adsorption of malachite green and Pb(2+) still follows the first-order kinetics.