Adsorptive removal of stable and radioactive Pb(II) isotopes from aqueous solution using bentonite, zeolite and perlite: characterization, isotherm and thermodynamic studies

In this study, stable and radioactive lead removal from aqueous solution by adsorption using bentonite, zeolite and perlite minerals obtained from various locations in Türkiye was studied in batch experiments. The adsorbents were first characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), and then the physicochemical properties were determined. The effects of various factors that influence adsorption, such as solution pH, adsorbent dosage, contact time, initial Pb2+ ion concentration, temperature and shaking rate, were studied. The adsorption of Pb2+ was modelled using the Langmuir, Freundlich and Dubinin–Radushkevich isotherms. The adsorption capacities of the minerals for Pb2+ followed the order: bentonite > zeolite > perlite, and the maximum adsorption capacities were 131.6, 36.1 and 21.5 mg g–1, respectively. The adsorption data fit well with the Langmuir isotherm. The bonding of lead ions on the adsorbents was confirmed by XRF and FTIR analyses after the adsorption process. The adsorption of Pb2+ ions on the adsorbents was spontaneous and endothermic. The adsorption process took place by cation exchange in addition to electrostatic interaction. Furthermore, radioactive 210Pb2+ adsorption on bentonite, zeolite and perlite was studied, with the analyte being analysed using a liquid scintillation counter. It was seen that in addition to Pb(II) ions, these minerals also adsorbed the radioactive decay products of 210Pb, which were 210Po and 210Bi. The removal percentages of 210Pb were 95%, 38% and 30% and those of 210Po were 75%, 60% and 74% for bentonite, zeolite and perlite, respectively.