DETECTION OF SURFACE HYDROXYL SPECIES ON QUARTZ, GAMMA-ALUMINA, AND FELDSPARS USING DIFFUSE-REFLECTANCE INFRARED-SPECTROSCOPY

Surface hydroxyl groups were detected on silica, gamma-alumina, quartz , and feldspar powders using diffuse reflectance Fourier transform inf rared (IR)-spectroscopy. Spectra were collected on all samples before and after heating in air to remove physisorbed H(2)0. On both natural and synthetic samples of quartz and feldspars, this treatment reveals a single IR-band at 3742-3745 cm(-1), which is attributable to termina l >SiOH groups at the mineral surface. Many previous studies have sugg ested that the speciation of H on feldspar surfaces in water can be mo deled based on the speciation of H on gamma-alumina and silica surface s. However, no definitive evidence of >AlOH groups analogous to those found on gamma-alumina was detected on the feldspars measured in this study. This strongly suggests that gamma-alumina surface hydroxyl grou ps should not be used as guides to the surface chemistry of feldspars. The IR spectra observed on the feldspars in this study cannot rule ou t the existence of either >AlOH20 or >Al-OH-Si< surface groups on feld spars in air, but such groups were not definitively observed in the IR -spectra. Models of surface protonation and dissolution rates in aqueo us solution might be improved by inclusion of terms describing either >AlOH20, >AlOH- and >AlO-2, or >Al-OH-Si< species, rather than >AlOH0, >AlOH2+, or >AlO- groups. Copyright (C) 1997 Elsevier Science Ltd.