Batch studies are routinely used to evaluate reaction kinetics of groundwater pollutants with mineral phases. To bridge a significant gap between laboratory results and real and complicated field conditions, the mineral-mediated abiotic reduction of 4-chloronitrobenzene (4ClNB), a model for common groundwater pollutants, was studied in flow-through columns, and the growth of goethite nanoparticles was quantified. The columns contained sand to which goethite nanoparticles were attached. Goethite nanoparticles were attached to the Ottawa sand through electrostatic attraction at pH 6.8. It was demonstrated that raising the pH to 9 would lead to the release of the particles. Short (20 pore volumes) and long (230 pore volumes) exposure of the goethite-coated sand grains to ferrous iron (Fe(II) and 4ClNB were carried out, and tracer studies were used to evaluate any changes in flow properties. At the end of the exposure, post-reaction particles from different heights in the column were characterized using X-ray diffraction and transmission electron microscopy. Particle size and phases then were compared to the pre-reaction particles elucidate the oxidative growth direction. The reduction of 4ClNB by goethite was also studied in batch reactors with the sand-conditioned buffer to investigate any effects of dissolved ions on the oxidative mineral growth process. Based on the number of electrons transferred to 4-ClNB from Fe(II) in both column and batch reactors, we expected that the volume of particles would approximately double. Results showed for the batch reactors the volume of particles almost doubled (1.9) and for column reactors, based on the reference used for comparison - as prepared original particles or particles detached from the sand without reaction - the volume of particles increased in a range from 1.4 to 2.7, indicating that the reduction of 4-ClNB resulted in oxidative mineral growth instead of the formation of new particles.

Probing the oxidative growth of goethite-coated sand grains in column reactors

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.