pH buffering downgradient of permeable reactive barriers | pH-Wertpufferung im Abstrom von Reaktionswänden
2006
Plagentz, Volkmar | Schäfer, Dirk | Köber, Ralf | Ebert, Markus | Dahmke, Andreas | Dethlefsen, Frank
Sequenced column experiments were conducted in order to assess the impact of elevated pH caused by two possible reactive media combinations for permeable reactive barriers (Fe°/Oxygen Release Compound (ORC) and Fe°/activated carbon) on the groundwater quality in a lignite sand. In the experiments, pH values > 9,5 downgradient of Fe° and ORC reactors were buffered to lower values by the lignite sand. In the lignite sand, pH fronts formed, propagating downgradient at a velocity that was 220–1,100 times slower than the groundwater flow velocity (0.71 and 0.83 m/d, respectively). The amount of base equivalents buffered in both experiments (52 and 7.3 meq/kg sediment, respectively) depended mainly on the different amounts of base equivalents present in the inflowing solutions. The majority of the base neutralization can be explained by the deprotonation of functional groups on mineral surfaces and organic carbon. The extent of other buffering mechanisms, such as mineral dissolution and pyrite oxidation, was limited in time. For the lignite sand examined here, high pH values downgradient of permeable reactive barriers will be limited to a narrow zone, even in the long term, and high pH values will not limit the possible implementation of a permeable reactive barrier.
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