关键词: 白云石, 钡白云石, 无定形相, 脱水, 分子动力学模拟

Abstract: Dolomite, one of the most widely distributed carbonate minerals on the Earth’s surface, is abundantly developed in ancient strata, but rarely exposed in modern marine environments. After decades of research, few low-temperature experiments have been reported to successfully synthesize ordered dolomite. The mineralization behavior of dolomite is one of the most intriguing mysteries. Conventional wisdom theories that Mg²⁺ hydration is the critical limit for Mg²⁺ to enter carbonate lattice. However, a recent study unveiled evidence questioning this premise and instead indicated that the structural constraints in the relevant amorphous precursor phase may play a more important role. Because transformation and crystallization of amorphous precursor phase in solution is a likely crystallization pathway for dolomite formation, and dehydration may have a pivotal effect on this process. Therefore, we carried out a study using molecular dynamics simulations to study the phase transition and dehydration process of amorphous precursors in Ca-Mg-Ba-CO₃ systems. The results show that the density increases significantly during the dehydration process, but the distances between metal cations and other ions are little affected and the total coordination number is unchanged. In terms of translational dynamics, the diffusion behavior of amorphous precursors in hydrated Ca-Mg-CO₃ and Ba-Mg-CO₃ systems (i.e., ACMC and ABMC) are similar, but the particle of ACMC is less mobile, hindering the aggregation of nucleation clusters. Thermodynamically, there is a significant difference in the dehydration enthalpy between ACMC and ABMC systems, with ACMC system having a higher dehydration enthalpy and the difficulty in losing the last few H₂O molecule from the structure, presumably limiting dolomite crystallization. This study systematically addressed the role of dehydration in controlling the crystallization of dolomite and norsethite and the findings of this study may provide insight into the “dolomite problem”.

Key words: dolomite, norsethite, amorphous phase, dehydration, molecular dynamics simulation