Fe0/pumice mixtures: from laboratory tests to permeable reactive barrier design

Permeable reactive barriers containing zero valent iron (ZVI-PRBs) represent an in situ technology for groundwater remediation. One of the main design issues of ZVI-PRBs is the determination of the expected lifespan. Therefore, the objective of the present work is to determine, by interpreting column experiments data through a first-order kinetic model, the thickness and duration of a hypothetical PRB constituted respectively by ZVI and by a ZVI/pumice mixture to be built for remediating groundwater contaminated by nickel at two different initial concentrations (40 and 8 mg/L). The kinetic constant values derived from this model are intended solely as an engineering tool for the design of ZVI systems and not as an interpretation of the actual reactions involving ZVI, water, and its constituents. Column test results show a linear decrease over time of the kinetic constant values. The use of the mixture implies an increase of the barrier thickness (from 2·5 to 15·5 times the ZVI thickness) but allows a reduction in the amount of ZVI needed to reach remediation objectives (from 84·5 to 87% considering 4 years of PRB operation) and an increase in the lifespan of the barrier (about 7·2 times for the lowest values of nickel concentration used).