SURFACE CHARACTERIZATION OF ACID-LEACHED OLIVINES BY X-RAY PHOTOELECTRON-SPECTROSCOPY

X-ray photoelectron spectroscopy was used to study the surface alterat ion of olivines (fayalite and forsterite) during acid dissolution (0.0 5 mol l(-1) H2SO4 at room temperature for one day). The abundances of Fe and Mg, relative to Si, in the near surface of olivines decreased a fter acid dissolution. The divalent cations in the fayalite were remov ed more readily than those in the forsterite. After acid dissolution, the Si 2s and O 1s spectra of fayalite were deconvoluted to contributi ons from unleached and leached phases. The Si 2s and O Is binding ener gies were higher for the leached phase relative to the unleached phase , and comparable to those of silicon dioxide (quartz and silica gel), indicating that SiO2 . nH(2)O formed on the mineral surface. Scanning electron micrographs of the leached olivine grains showed a harshly et ched structure for fayalite and a locally etched structure for forster ite, indicating that the dissolution proceeded heterogeneously.