Synthesis and characterization of a new magnetic bio-adsorbent using walnut shell powder and its application in ultrasonic assisted removal of lead

In this paper, we report the use of a low-cost magnetic adsorbent from walnut shell (LMWS) as an efficient lead remover. We tried to grow magnetic domains on top of the LMWS surface via coprecipitation of minimum amounts of Fe2+ and Fe3+ ions. The results obtained from the kinetic experiments confirmed a fast accessibility of the Pb2+ ions to the adsorbent surface, reaching equilibrium within a few minutes. The experimental parameters including solution pH, adsorbent dose, concentration of metal ion solution, adsorption time, and solution temperature were optimized to find the maximum capacity of the magnetic walnut shell (MWS) bio-adsorbent. The adsorption of Pb(II) ions by MWS showed a slightly better fit with the Langmuir model compared to the Freundlich one. The experimental data obtained was tested using two different kinetic models. The pseudo-second order kinetic model represented this data very well. Moreover, the adsorbent was reused for several cycles. After elution of sorbent with a suitable eluent (HCl, 0.10 M) the obtained results showed no significant reduction in the adsorption capacity and the magnetic properties of adsorbent. It was notable that the metal adsorption was quite fast and could be completed within 4 minutes due to the absence of an internal diffusion resistance. (C) 2017 Published by Elsevier Ltd.