Background and Objectives: Existence of Heavy metals in water resources is one of the most important environmental problems in many countries. These metals have dangerous effects on human health. The purpose of this study is  to investigate and compare lead removal by nanometer and millimeter absorbents of Zizyphus Spinachristi fly ash.
Materials and Methods: This study was non-continuous experiment which was implemented under laboratory conditions with and by changing effective factors such as pH (3, 4, 5, 6, 7, 8), contact time (5, 10, 15, 30, 45, 60, 90, 120 minutes) and adsorbent concentration (1, 2, 5, 10, 20 and 50 mg/ L). The data was fitted based on four models including Ho et al, Lagergern, Lungmuir and Freundlich which the first two models used for absorption kinetic and the latter two considered as absorption isotherm.
Results: The Result of this study showed that as the pH increases from 3 to 5 adsorption efficiency increased as well. Furthermore, when pH was over 5, the metal ions settled down. With increasing contact time, adsorption efficiency increased as well. With increasing the amount of nanometer as an adsorbent, removal efficiency increased and then decreased. Also the adsorption process followed precisely Ho et al kinetic and Langmuir isotherm, for both absorbents.
Conclusion: Based on the obtained results, specific area of the nano particles was more than millimeter particles (29.56 m2/g & 17.80 m2/g), therefore adsorption capacity of nano absorbent was four times more than adsorption capacity of millimeter (19.93 mg/g & 17.80 mgr/g). Furthermore, the findings concluded high capability of nano particles towards Sorption of lead ions (Pb) from aqueous solutions.