Anatase nanoparticles on supergene platinum–palladium aggregates from Brazil: Titanium mobility in natural waters

Supergene aggregates of platinum–palladium (Pt–Pd) intermetallic compounds from the Córrego Bom Sucesso alluvial deposit, Minas Gerais, Brazil, are coated with abundant, poorly crystalline nanoparticles of anatase (TiO2). The anatase coating is widespread, suggesting that the surface of the Pt–Pd grains catalytically destabilised Ti, which was likely dissolved by organic ligands in the ground waters. Association of TiO2 nanocrystallites with organic matter further suggests that biogenic processes could have mediated their formation. These anatase-coated Pt–Pd grains demonstrate an unexpected Ti mobility in supergene environments.

► Titanium was mobile within alluvial sediments.
► Titanium precipitated on supergene platinum–palladium grains as titanium-dioxide nanoparticles.
► Organic matter associated with the nanoparticles suggests biological mediation.