(332b) Abiotic Degradation with Reactive Iron Mineral Coatings in Anaerobic Sediment

Abiotic dehalogenation with reactive iron minerals plays an important role in the natural attenuation of chlorinated organic solvents. These reactive iron minerals are most significant in redox transition zones. However, there are a number of challenges in collecting anaerobic cores representative of the subsurface environment. In this study, an anaerobic sediment core was collected from an industrial site with 1,4-dichlorobenzene and 4-chloroaniline plumes. With the redox condition preserved, a number of approaches including sequential extraction were applied to quantify reactive iron mineral coatings. Results revealed an abundance of siderite, pyrite, mackinawite, magnetite, and iron oxyhydroxides in three redox transition zones. Experiments were carried out to evaluate abiotic dehalogenation of 1,4-dichlorobenzene. The reaction rate followed a second order rate expression that was a function of the 1,4-dichlorobenzene and the reactive mineral coatings present in the sediment; for the three transition zones rate, constants for the dominant reactive mineral coatings were obtained. The time to achieve 90% removal ranged from 50 to 200 days for the zones studied. To degrade 4-chloroanaline, persulfate was applied with the reduced iron mineral coatings in the sediments. Persulfate forms SO₄^-., a radical, and a strong and effective oxidizing agent. Degradation rates revealed first-order rate constants with 90% removals requiring 9 and 22 hours. From these studies, the degradation pathways and models for target constituents of concern can be used to enhance these processes in contaminated subsurface systems.