The interactions of Co, Mn and water with calcite surfaces

Abstract

The interactions of Co, Mn and water with surfaces of single crystal calcite (CaCO 3) have been examined using surface analysis techniques (primarily X-ray photoelectron spectroscopy, XPS) and a specimen transfer system. The metals were deposited on the calcite by evaporation to give submonolayer concentrations. For coverages of Co as low as 0.16 ML, the metal clearly appears in both metallic and oxidized states. Immersion in deionized water completely converts all Co to a compound most consistent with the hydroxide. As previously observed for Mn, some of the Co is removed from the surface during immersion. The rate of removal of Co is two times faster than that of Mn. Further, these rates are about three orders of magnitude slower than that reported for the dissolution of bare calcite. Recently reported solution experiments suggest that Mn cations are adsorbed substitutionally from aqueous solution while most other metals, including Co, are adsorbed in a hydrated form. The significance of our results in light of the conclusions of these solution experiments is discussed.