Adsorption kinetics and molecular interactions of lead [Pb(II)] with natural clay and humic acid

Currently, the contamination by lead has become a serious issue to the environment, and many approaches are continuously been searched for its removal from the environment. In the present study, the adsorption potential and interaction of lead [Pb(II)] with natural clay and humic acid were investigated. X-ray diffraction analysis revealed quartz as a dominant mineral in natural clay. Maximum adsorption capacity of both natural clay and humic acid for Pb(II) was 25.07 and 19.16 mg/g, respectively, after the incubation time of 180 min and adsorbate and adsorbent concentrations of 20 mg/L and 10 g/L, respectively. Adsorption capacity of clay was found to be 1.3-folds greater than that of humic acid. Pb(II) adsorption on clay and humic acid was according to the Langmuir isotherm and followed the pseudo-second-order and intraparticle diffusion model kinetics. Fourier transform infrared spectra revealed that Si–O–Si and OH⁻ groups in clay were involved in the interaction with Pb(II); and carboxylic acid, phenolic and alcoholic groups and alkyl halides in humic acid were involved in the interaction with Pb(II). Scanning electron microscopy and energy-dispersive X-ray spectra analysis revealed that Pb(II) adsorption on clay and humic acid occurred by replacement of Mg and Al ions, potentially by ion exchange mechanism. Overall, the results concluded that natural clay and humic acid are promising adsorbents for limiting the mobility of Pb(II) ions in the soil system and aquatic environment, and this could be an effective method for lead waste management.