Impact of Mineral Fouling on Hydraulic Behavior of Permeable Reactive Barriers

Abstract

This paper describes reactive transport simulations conducted to assess the impact of mineral fouling on the hydraulic behavior of continuous-wall permeable reactive barriers (PRBs) employing granular zero-valent iron (ZVI) in carbonate-rich alluvial aquifers. The reactive transport model included a geochemical algorithm for simulating corrosion and mineral precipitation reactions that have been observed in ZVI PRBs. Results of simulations show that porosity and hydraulic conductivity of the ZVI decrease over time and that flows are redistributed throughout the PRB in response to fouling of the pore space. Under typical conditions, only subtle changes occur within the first 10 years (i.e., duration of the current field experience record with PRBs), and the most significant changes do not occur until the PRB has operated for at least 30 years. However, changes can occur sooner (or later) if the rate at which mineral-forming ions are delivered to the PRB is higher (or lower) than that expected under typical conditions (i.e., due to higher/lower flow rate or inflowing ground water that has higher/lower ionic strength). When the PRB is more permeable than the aquifer, the median Darcy flux in the PRB does not change appreciably over time because the aquifer controls the rate of flow through the PRB. However, seepage velocities in the PRB increase, and residence times decrease, due to porosity reductions caused by accumulation of minerals in the pore space. When fouling becomes extensive, bypassing and reductions in flow rate in the PRB occur.

Performance of a PRB for the Remediation of Acidic Groundwater in Acid Sulfate Soil Terrain

“…Several researchers (Karvonen 2004;Komnitsas et al 2007;Li and Benson 2005;Liang et al 2003;McMahon et al 1999;Puls et al 1999a;Sarr 2001;Vogan et al 1999;Yabusaki 2001) have reported that armouring on the surface of reactive materials and chemical clogging of pores, by precipitated compounds during chemical reactions inside the PRB, decrease the long-term performance parameters such as reactivity, porosity and permeability. Significant concerns relating to precipitation of iron and aluminium oxides and hydroxides also exist in alkaline PRBs with acidic groundwater in ASS terrain because their solubilities are pH-dependent.…”

ZVI (Fe0) Desalination: Stability of Product Water

“…This structuring allows the ZVI to actively remove divalent and trivalent cations from the water [2] and convert them into effective catalysts [133]. Both oxygen evolution [26,70,134] and hydrogen evolution [1,70,71,105,108,109,[134][135][136][137][138] have been associated with the placement of ZVI in water.…”

“…Some PRB designers have attempted to overcome the adverse effect of permeability destruction by creating a PRB with a higher initial permeability than the surrounding aquifer [108]. Porosity, φ, reduction in a ZVI PRB can be modelled by assuming a pseudo-first order corrosion reaction and by using hydraulic conductivity (K c ) to represent permeability (k p ) where [109]:…”

Dimensioning metallic iron beds for efficient contaminant removal

“…Accordingly, the precipitation of iron corrosion products and other secondary minerals is regarded as perturbing side effect yielding reactivity and porosity loss [2,14,16,17]. Accordingly, the design of a PRB requires profound knowledge of local water flow velocity (residence time), aquifer porosity, influent contaminant concentration.…”

“…gravel, pumice, sand) [2,14]. Because of the volumetric expansive nature of the process of iron corrosion [15], the porosity of the filtrating systems certainly decreases with increasing service life, possibly yielding complete permeability loss system (filter clogging) [16,17]. The filling of the pore volume by corrosion products is necessarily coupled with improved size exclusion capacity.…”