engleski

Ion exchange capacity of Pb^2+ on natural zeolites under static and dynamic conditions

Ion exchange is an attractive method for removing heavy metals from wastewater, particularly when natural zeolites as low-cost minerals, are used as ion exchanger [1]. The main objective of this study is to evaluate the capacity of zeolite rich tuff from Vranjska Banja (grain size 0.6-0.8 mm) in the process of removing of Pb^2+ from an aqueous solution under static and dynamic conditions, at constant temperature of 20 oC. The batch studies were performed by equilibrating zeolites during three days with different concentration of Pb^2+, at solid-liquid ratio of 0.01, and with shaking condition. The data obtained from the batch studies were fitted to Freundlich and Langmuir isotherm, from which the cation exchange capacity has been calculated (57.14 mg /g zeolites). This value corresponds to 22.42 % of theoretical ion exchange capacity (TEC) [2]. Dynamic conditions of the process were performed using a fixed bed experimental apparatus filled with natural zeolite, at constant influent concentration (207.21 mg /L Pb^2+) and flow rate (1 mL/min). In the first cycle of ion exchange in the column, the breakthrough curve (S-shape) is flatten, but in the second cycle is sharp with a much shorter adsorption zone [3]. The capacity at the breakthrough point in the first cycle is 7.29 mg Pb^2+/g, while at the second cycle is 100.06 mg Pb^2+/g zeolite. This can be explained by a slow establishment of stationary conditions during the first cycle, (degasification of pores, solid – liquid contact area), as well as higher exchangeability of the ions, due to the activation of more number of exchangeable sites at each subsequent cycle.

ion exchange; wastewater; heavy metal ions

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