Naturally-occurring iron oxide and oxyhydroxide nanoparticles provide a reactive surface that has been widely shown to enhance the reduction of nitroaromatic compounds (NACs) by Fe(II). NACs are a common class of groundwater pollutants and are used as pesticides, herbicides, textile dyes, and explosives. In many natural aquifer systems, iron oxide minerals are found as components of coatings on sands, silts, and other sediments. These materials interact with groundwater pollutants continuously. To better emulate these field conditions, continuous flow columns were used to study the reduction of 4-chloronitrobenzene (4-ClNB) by Fe(II) when exposed to hematite rich sediments. In well controlled batch reactors prepared with hematite nanoparticles, the 4-ClNB reduction occurs concurrently with oxidative mineral growth of a mixture of hematite and goethite. Flow-through reactors were prepared by packing columns with sands coated with varying amounts of the same hematite nanoparticles as were used in the batch reactors. In the flow-through reactors, goethite was also observed as a product of the oxidative mineral growth, with morphology similar to what was observed in the batch reactors. Results tracking the rates of reductive degradation of the 4-ClNB and evolution of the phase composition of the iron oxides at different positions within the column reactors will be presented. Results highlight the importance for understanding mineral phase growth and impact of aqueous conditions during contaminant fate modeling.

Evolving mineral reactivity of hematite-coated sands during reduction of 4-chloronitrobenzene by Fe(II)

ACS Spring 2022

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