Formation Processes and Impacts of Reactive and Nonreactive Minerals in Permeable Reactive Barriers

摘要

Mineral precipitates in zero-valent iron PRBs can be classified by formation processes into three groups: 1) those that result from changes in chemical conditions (i.e., changes in pH, e.g., calcite); 2) those that are a consequence of microbial activity (i.e., sulfate reduction, e.g., mackinawite); and, 3) those that are the result of iron metal instability and corrosion (e.g., magnetite). The presentation will explore these mineral formation processes and consequences with respect to the hydraulic and reactive longevity of PRB systems. The formation of mineral precipitates in PRBs can impact remedial performance. As minerals precipitate in iron walls they occupy volume and therefore reduce porosity and permeability of the reactive zone. In this way the hydraulic performance of PRBs (e.g., residence time, capture zone) could degrade through time as the effective porosity of the iron wall approaches or exceeds that in the adjacent aquifer. For example, preferential mineral accumulation in regions of a PRB resulting from higher inputs of dissolved solutes may lead to increases in groundwater residence times. However, adjacent regions of the reactive barrier may experience greater throughput and decreased residence times, potentially leading to contaminant breakthrough. A second largely unexplored effect of