SURFACE HYDROXYL CONFIGURATION OF VARIOUS CRYSTAL FACES OF HEMATITE AND GOETHITE

The surface properties of oxides and hydroxides depend on their surfac e hydroxyl configuration (SHC). Unfortunately, the SHC of the various Fe (hydr)oxides has not been systematically studied to date. This pape r reports the SHC of the hematite {100}, {110}, {012}, {104}, {018}, { 113}, and {001}, and the goethite {100}, {010}, {110}, and {021} faces , which are the most common in natural and synthetic specimens. Both m inerals exhibit marked differences between faces, particularly with re gard to the presence and proportion of singly, doubly, and triply coor dinated OH groups. Pairs of contiguous singly coordinated OH groups, w hich are involved in the specific adsorption of phosphate and other io ns, occur on all the goethite faces studied, but not on those of hemat ite. According to the hypotheses inherent in some models, the variable SHC of hematite and goethite faces should result in marked difference s in proton adsorption and, hence, surface charging properties. (C) 19 96 Academic Press, Inc.