Nanoparticulate goethite, akaganeite, hematite, ferrihydrite and schwertmannite are important constituents of soils, sediments and mine drainage outflows. These minerals have high sorption capacities for metal and anionic contaminants such as arsenic, chromium, lead, mercury and selenium. Contaminant sequestration is accomplished mainly by surface complexation, but aggregation of particles may encapsulate sorbed surface species into the multigrain interior interfaces, with significant consequences for contaminant dispersal or remediation processes. Particularly forparticle sizesontheorder of1–10 nm,the sorptioncapacityandsurface molecular structure also may differ in important ways from bulk material. We review the factors affecting geochemical reactivity of these nanophases, focusing on the ways they may remove toxins from the envi- ronment, and include recent results of studies on nanogoethite growth, aggregation and sorption processes.
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