Grain size of activated carbon, and untreated and modified granular clinoptilolite under freeze-thaw: Applications to permeable reactive barriers

Permeable reactive barriers are used to adsorb contaminants from soil water. Their fillings are granular materials whose stability under freezing conditions has not been demonstrated. In this research, three granular materials (activated carbon, raw clinoptilolite and a nutrient amended clinoptilolite) were subjected to freeze-thaw cycles at different moisture conditions, in order to simulate their use in permeable reactive barriers in areas of freezing ground. The <250 μm fraction, which will potentially accumulate grain fragments, showed no change for the carbon, but an increase from ∼1% to ∼3% abundance by volume for the clinoptilolite with modes at 100-200 μm. SEM images show cracks in the zeolite grains, forming fragments of the size observed in the particle size data. These findings may have implications for the long-term permeabilities of reactive barriers operated in areas of freezing ground.