Surface characterization of the water-treated olivine under different pH conditions at 25°C

Natural olivine crystals (Fo91) were subjected to water treatment at 25°C under different pH conditions covering 1 to 12. Hydrogen enriched surface layer with the thickness of about 20 nm was detected with X-ray photoelectron spectroscopy (XPS) and resonant nuclear reaction analysis (RNRA). H+ or H3O+ occupies the vacant octahedral sites in the Mg and Fe depleted surface layer at low pH. Molecular water penetrates along defects as deep as 200 nm. On the contrary, Si is selectively leached out and hydroxyl species are formed at high pH. This contrasting surface chemistry results from the difference in the surface species which are responsible for dissolution process under acidic and basic conditions.