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Determination of the heavy metal concentration profile through a zeolite barrier used in groundwater remediation

Permeable reactive barriers (PRBs) are reactive treatment zones for intercepting and reacting with contaminants dissolved in groundwater. PRBs are typically installed as permanent structures across the flow path of a contaminant plume. Prior to their installation, it is necessary to investigate the contaminant fate and transport as the contaminated groundwater moving through the PRB requires sufficient retention time for immobilization of the contaminants. Flow-through column experiments were performed for simulation of dynamic field conditions and to quantify the movement of contaminants (Cd+Zn) relative to groundwater flow. The distribution coefficient Kd (L/g) was calculated as it is a very important parameter in estimating the potential for the sorption of dissolved contaminants into natural zeolite. The retardation Rd (-) of contaminants, which is the degree of reduction of velocity due to the sorption, was calculated from the Kd values. Based on the column experimental results, the spreading of Cd and Zn contaminants through the different barrier thickness (x) was predicted by a simple analytical pulse model, by calculating the values of the hydrodynamic dispersion coefficient DL (m2/min) and the retardation hydrodynamic dispersion coefficient DLR (m2/min). According to obtained results, Zn was less distributed and retarded within zeolite than Cd. By reducing the residence contact time, distribution and retention of Zn becomes better due to less pronounced competition of Cd and Zn for the same active sites in zeolite at increased flow rates. Results show that a larger barrier thickness produces an extended retention time, but this increases investment costs.

zeolite, cadmium, zinc, permeable reactive barrier, Brigham method, analytical pulse model

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