Removal of copper and zinc from ground water by granular zero-valent iron: A dynamic freeze-thaw permeable reactive barrier laboratory experiment

Permeable reactive barriers (PRBs) use solution-media interactions for contaminant removal from ground and surface waters. When located in a cold region subjected to freeze-thaw cycling, these liquid-solid phase interactions may be detrimental to PRB performance. This study presents a laboratory based assessment of contaminant removal using granular zero-valent iron (ZVI) under freeze-thaw conditions. Freeze-thaw induced changes to simulated PRBs, contained within Darcy boxes, subjected to 0, 21 and 42 freeze-thaw cycles were assessed using the flow of both reactive and conservative solutions. The reactive contaminants, Cu2 + and Zn2 + ions, were removed from the pore water during solution flow and freeze-thaw cycling. The hydraulic retention time within the reactive media as assessed by a conservative tracer, decreased by 15-18% after the first set of freeze-thaw cycling and remained constant after the second set of freeze-thaw cycling. A decrease in the uniformity of the particle size distribution and the agglomeration of particles were observed; however there was no change in the hydraulic conductivity within the variance associated with the calculation method. Analysis of the solid particles suggested the contaminant metals were not concentrated in the < 212 μm fines that were generated during the experiment. The results obtained suggest that ZVI is suitable for the inclusion in sequenced PRBs for the remediation of metal contaminants in cold regions.