Abstract
The adsorption of divalent heavy metal ions, M2+(Co2+, Cu2+, Zn2+, Cd2+, Pb2+), on a calcite surface was investigated at 25.0°C. The concentrations of metal ions in solution (CM) and on calcite surface (CM,S) were determined by ICP-MS. The slopes of plots of log D (D = CM,S/CM) as a function of pH were obtained as 2 for Cd2+ and Pb2+, whereas those for Co2+ and Zn2+ were between 1 and 2. The distribution ratio of these ions dose not depend on the calcium concentration. An analysis of the results by taking into consideration the formation of the hydroxo complex of the metal ions in solution revealed that the chemical species adsorbed on a well-developed calcite surface are M(OH)2. On the other hand, the distribution ratio of Cu2+ dose not depend on the pH, and increases upon decreasing the calcium comcentration. Thus, the adsorbed species was estimated to be Cu(CO3). The adsorption of neutral species prevents the accumulation of positive charge of the crystal surface, and minimizes the electrical repulsion between the surface and adsorbing species. The distribution ratio on a rough surface created by grinding the calcite crystal was also studied. The distribution ratio on the rough surface was higher by 1-2 orders than that of the smooth surface.
