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

tThe 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 beforeand after lead sorption was performed by determination of textural properties, by scanning elec-tron microscopy and X-ray spectroscopy in energy-dispersive mode (SEM–EDS), transmission electronmicroscopy (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 thenatural and Fe(III)-modified zeolite respectively) confirmed an activated chemical sorption. Desorptionexperiments indicated that lead was irreversibly sorbed on both zeolites. XRPD, TEM and SEM resultsshowed that modification of the natural zeolite with Fe(III) ions did not change its crystal structure andiron is mainly located at the zeolite surface, likely in form of amorphous iron oxy-hydroxides. Specificsurface area significantly increases after modification of the natural zeolite with Fe(III) ions (from 30.2for the natural to 52.5 m2/g for Fe(III)-modified zeolite). Characterization of both lead saturated sorbentssuggested that besides ion exchange, lead is both chemisorbed and precipitated at their surfaces, andpresence of amorphous iron in Fe(III)-modified zeolite favors sorption of lead.