矿床地球化学国家重点实验室知识库

The mechanisms of quartz dissolution are intricately affected by pH conditions and electrolyte types. While most of previous studies have focused on mechanisms of quartz dissolution under a single specific condition (e.g., temperature, pH, saturation or electrolyte type), this study investigates the molecular level mechanisms at combinations of electrolyte and pH conditions, which are more complicated but closer to the reality. Under neutral and alkaline pH conditions, with Ca, Mg or Na aqua ion in the solution, the dissolution of Q1(Si) and Q2(Si) sites on quartz surface, which represents the predominant part of the quartz dissolution story, was investigated by first-principles quantum chemistry calculation methods. Our results confirm that the dissolution of quartz can be significantly enhanced with the presence of electrolytes under neutral pH conditions. However, under alkaline pH conditions, the surface complexes of aquo ions are different, depending on where and how those electrolytes bond onto quartz surfaces. Energy barriers of all possible hydrolysis reaction pathways are carefully calculated. The activation energies for the reaction between negatively charged quartz surface and HO have never been reported before. Our activation energy results are closer to the experimental values than previous calculations, suggesting the cluster models and theoretical levels used here are more reasonable. Such information provides a molecular-level understanding about the differences of quartz dissolution rates between pure water and ion-containing solutions.