You are here:
Hydroxyl radical scavenging by solid mineral surfaces in oxidative treatment systems: Rate constants and implications
Citation:
Rusevova Crincoli, K. AND Scott G. Huling. Hydroxyl radical scavenging by solid mineral surfaces in oxidative treatment systems: Rate constants and implications. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 169:115240, (2020). https://doi.org/10.1016/j.watres.2019.115240
Impact/Purpose:
Advanced oxidation treatment processes used in various applications to treat contaminated soil, water, and groundwater involve powerful radical intermediates, including hydroxly radicals (•OH). Inefficiency in hydroxyl radical (•OH)-driven treatment systems is a significant limitation of water, groundwater, or soil oxidative treatment systems. Previously, the assessment of the role(s) of non-target species have been focused entirely on aqueous phase species. However, solid species that react with reactive oxygen species (ROSs), may also be present, scavenge radicals, and negatively impact treatment efficiency. In this study, the role of solid phase media in oxidative treatment systems was measured for the first time. A kinetic analysis and laboratory testing methods were developed for the purpose of determining the surface scavenging rate constant (k≡S). k≡S was determined for three minerals in two oxidative treatment systems, and a consistent trend was established: k≡S,silica ~ k≡S,alumina > k≡S,MMT. The •OH surface scavenging rate for unconsolidated porous media comprised of 7% (wt/wt) of these minerals was projected to be 5 orders of magnitude greater than •OH reaction with aqueous phase species and scavengers. This research can be used to develop new methods and provide guidelines that limit surface scavenging and improve treatment efficiency.
Description:
Inefficiency in hydroxyl radical (•OH)-driven treatment systems involves scavenging reactions where •OH reacts with non-target species in the aqueous and solid phases. Here, •OH were generated in Fe- and UV-activated hydrogen peroxide (H2O2) (Fe-AHP, UV-AHP) systems where rhodamine B dye served as a quantitative metric for •OH activity. Kinetic analysis methods were developed to estimate the specific •OH surface scavenging rate constant (k≡S). In the Fe-AHP system, k≡S for silica (3.03×106 1/m2×s) and alumina (4.30×106 1/m2×s) were similar. Accounting for nonproductive losses of H2O2, k≡S for montmorillonite (MMT) (≤ 1.01×105 1/m2×s) indicated that surface scavenging rates varies between minerals. In the UV-AHP treatment system, k≡S for silica, alumina, and MMT were higher by factors of 1.5, 1.7, and 4.6, respectively, over k≡S from the Fe-AHP system, and k≡S for MMT was significantly less than silica and alumina. A consistent trend of k≡S was established for the three minerals tested: k≡S,silica ~ k≡S,alumina > k≡S,MMT. Assuming unconsolidated porous media comprised of 7% (wt/wt) for each of these minerals, projections for •OH surface scavenging was 5 orders of magnitude greater than •OH reaction with aqueous phase species and scavengers. A conceptual model was proposed involving scavenging sites on solid phase surfaces that far outnumber sorption sites.
URLs/Downloads:
DOI: Hydroxyl radical scavenging by solid mineral surfaces in oxidative treatment systems: Rate constants and implications
Free access through PubMed Central