Divalent Lead in Aqueous Solution Changes the Surface Morphology of Dolomite and Inhibits Dissolution

Abstract

In groundwater systems, heavy metal ions as solutes (e.g., Pb) can adsorb onto the surface of calcite group rocks and influence their dissolution processes. The dolomite surface was examined using field emission scanning electron microscopy (SEM) and various characterization tools and the changes in water chemistry indexes were reviewed throughout the dissolution process. Pb adsorption on the dolomite surface was evident after 15 days of exposure to 1 mg/L or 50 mg/L divalent Pb salt solutions; the Pb surface phase was mainly PbCO3 with an octahedral ligand structure. SEM images show that dolomite in divalent Pb salt solutions can lead to the surface morphology exhibiting curved dissolution steps. In the closed system with Pb (1 mg/L), the total alkalinity and conductivity of the solution were lower than in the Pb-free system, and the pH difference was slight, indicating that the dibasic metal ion Pb inhibited the dolomite dissolution process. Combined with the composition of the final solid phase, it is suggested that the dolomite surface preferentially adsorbs Pb2+ on the active sites and that the newly grown solid phase is PbCO3 possesses an octahedral ligand structure. Part of the surface-active site is occupied, resulting in a change in the dissolution profile, and thus preventing further development of the dissolution profile. Ultimately, the entire dolomite surface area is prevented from dissolution. The results of this study suggest that Pb2+ may be an effective inhibitor of dolomite dissolution and may help to further refine the geological carbon sink.