Characterization of lead sorption by the natural and Fe(III)-modified zeolite

Abstract

The influence of contact time, temperature and particle size on lead sorption by the natural and Fe(III)-modified zeolites was investigated. Characterization of the natural and Fe(III)-modified zeolite before and after lead sorption was performed by determination of textural properties, by scanning electron microscopy and X-ray spectroscopy in energy-dispersive mode (SEM-EDS), transmission electron microscopy (TEM) and X-ray powder diffraction (XRPD) analysis. Lead sorption kinetics at 303-333 K, best represented by the pseudo-second order model and activation energy (13.5 and 8.5 kJ/mol for the natural and Fe(III)-modified zeolite respectively) confirmed an activated chemical sorption. Desorption experiments indicated that lead was irreversibly sorbed on both zeolites. XRPD, TEM and SEM results showed that modification of the natural zeolite with Fe(III) ions did not change its crystal structure and iron is mainly located at the zeolite surface, likely in form of amorphous iron oxy-hydroxides. Specific surface area significantly increases after modification of the natural zeolite with Fe(III) ions (from 30.2 for the natural to 52.5 m(2)/g for Fe(III)-modified zeolite). Characterization of both lead saturated sorbents suggested that besides ion exchange, lead is both chemisorbed and precipitated at their surfaces, and presence of amorphous iron in Fe(III)-modified zeolite favors sorption of lead.