Activation of Firmiana Simplex leaf and the enhanced Pb(II) adsorption performance: equilibrium and kinetic studies

Although various biosorbents have been reported effective to purify wastewaters containing heavy metals, the high tendency to decomposition in the environment makes them unsuitable for long-term persistent utilization. In this paper, a simple and new activation method was proposed to mineralize the Firmiana Simplex leaf (FSL) into an enhanced adsorbent for Pb(II) removal from aqueous solution. The leaves activated at various temperatures were characterized with BET N(2) adsorption test, FT-IR test and XRD test. After activation, the mass percent of inorganic components (including whewellite, quartz, phosphate and calcite) increased and the specific surface area increased from 0.08283 to 9.32 m(2)g(-1) with the increasing activation temperature (AT) from 100 to 400 degrees C. Proper activation temperature (200 degrees C) helps to preserve the beneficial groups (amine and carboxyl). The affinities of the adsorbents towards Pb(II) were increased with increasing AT from 300, 100, 200 to 400 degrees C according to the adsorption isotherms. The adsorbent activated at 200 degrees C (AL2) was found most suitable for Pb(II) adsorption regarding the high yield efficiency (36.52%), high Pb(II) adsorption capacity (136.7 mg g(-1) by Langmuir model), high adsorption affinity (H type isotherm) and rapid adsorption rate (within 20 min by kinetic study). The Pb(II) removal efficiency of AL2 was obviously affected by the solution pH rather than by the adsorbent dosage. The adsorption was viewed as a chemical process based on IR spectra along with a physical process based on the correlation between the average pore size of the adsorbent and the adsorption capacity. The activation method proposed in this paper was proved effective and potentially applicable in the treatment of Pb(II) polluted wastewaters.