Humic acid and nano-zeolite NaX as low cost and eco-friendly adsorbents for removal of Pb (II) and Cd (II) from water: characterization, kinetics, isotherms and thermodynamic studies

Abstract

Humic acid as a green-sorbent was synthesized from marine sediments. While kaolin was modified to nano-zeolite NaX. Different tools such as FT-IR, SEM, EDX and XRD were applied to confirm the characteristics of the generated green-sorbents. Different factors such as pH, contact time, sorbent dosage, initial metal ion concentration, temperature and interfering ions were carefully examined and used to optimize the batch adsorption process for Cd2+ and Pb2+. A small dose of nano-zeolite of 100 mg was required to attain the maximum adsorption of Pb2+ at pH about 7, shacking time at 60 min and Pb2+ concentration at 30 ppm. Also, the maximum sorption capacity of Cd2+ ions on nano-zeolite was achieved in a neutral medium and very short contact time implying the economic feasibility of the adsorption process. In the case of humic acid, the maximum removal capacity for Pb2+ and Cd2+ was operated at acidic medium and shacking time was 40 min. Metal ions remediation results were evaluated by some adsorption isotherm models at different temperatures. The kinetic and thermodynamic variables were also computed. The data fitted very well with the linear Langmuir and the pseudo-second-order model implying a favourable adsorption process. The sorption of Cd2+ and Pb2+ was regulated by both external mass transfer and intraparticle diffusion steps over the whole range of concentrations, as shown by the results. The metal ions removal percentage from four real water samples by green sorbents were applied and provides good evidence of two sorbents as promising eco-sorbent for removal of heavy metal ions.