The presence of heavy metals in industrial effluents has become a matter of environmental concern because of their reported toxic and carcinogenic impacts. Many industrials such as mining, tanning, jewellery, chemical, metallurgical, electrical, galvanization, and other electroplating processes discharge wastewaters containing heavy metals such as lead, cadmium, chromium, nickel, and zinc. The conventional methods for wastewater purification include chemical precipitation, ion exchange, adsorption, etc. The bentonite and modified bentonite (Metagel ® ) used as the adsorbent, in the present study, were bentonite obtained from Semnan region, Iran. In contact with water, they swelles and forms a very stable colloidal suspension with nano size particle. They were used as low cost nano adsorbents for the removal of Cr 3+ , Ni 2+ , Pb 2+ , Cd 2+ , and Zn 2+ from aqueous solutions. This project was carried out in a batch system and the effect of various parameters such as contact time, initial concentration of metal ions, pH, and adsorbent dosage by Response Surface Modeling were studied. The Minitab software has been employed for modeling. Metal ions concentration ranged 5 to 125 mg.L -1 , range of adsorbent dosage from 1 to 8 g.L -1 , and range of contact time was 10 to 210 min. The adsorption rate and sorption capacity of metal ions could be significantly improved by increasing pH values but at higher pH, precipitation was occurred along with adsorption. The efficiency of removal of metal ions by Metagel ® was higher than bentonite, because its sorption capacity was higher. The metal ions concentration has been determined in wastewater samples collected from Zoob Ahan and Hessa. Many factors, such as the ionic radius of the hydrated ions, the hydration energy of the metal ions and structure of clays, influence the selectivity differences observed between the metal ions and another. Different two-parameter sorption isotherm models such as Langmuir and Freundlich were used to fit the equilibrium data.
