Divalent Cd and Pb uptake on calcite [10(1)over-bar4} cleavage faces: An XPS and AFM study

The interaction of divalent Cd and Ph with the {1014} cleavage faces of calcite has been investigated with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Analysis of the {1014} cleavage planes of calcite was carried out with X-ray photoelectron spectroscopy (XPS) after exposure to divalent inetal-bearing Solutions ill the 0. 1-100 mu M concentration range for times ranging from1 it) 24 h. The uptake of Cd2+ by calcite was determined to be greater than that of Pb2+ under similar experimental conditions (1 mu M. pH 8.2, 24 h exposure time), In both cases, the majority of the divalent metal was postulated to exist in a surface precipitate, AFM results, showed that the exposure of calcite to a 1 mu M Pb2+ solution resulted in ellipsoidal surface growths that were attributed 10 the nucleation of a PbCO3 bulk phase. In the Cd circumstance, AFM showed comparatively flat growth features forming oil the calcite Surface (even at concentrations down to 0. 1 mu M, where the solution Would be expected to be undersaturated with respect to Cd bulk phase,,, These features were attributed to a (Ca,Cd)CO3 solid Solution. The individual exposure of these Cd/CaCO3 and Ph/CaCO3 samples to water pre-equilibrated with calcite (metal free) for I h led to the removal of no more than 20% of the divalent metal, suggesting that if there was all adsorbed Pb or Cd complex initially on the calcite surface, it was an minority species compared to the precipitate phase, Fxposure of calcite to 100 mu M Cd and Ph resulted in the accumulation of precipitate on the calcite surface presumably due to the divalent metal initial solution concentrations exceeding the solubility products of CdCO3 and PbCO3, respectively. (c) 2005 Elsevier Inc. All rights reserved.