方解石族矿物固溶体的溶解热力学及其对重金属在固－液两相中分配的影响

方解石晶格中的Ca2+位置可以容纳Mn2+、Cd2+、Zn2+、Co2+、Ni2+、Pb2+等二价阳离子，从而在自然界中形成一系列含重金属的具有方解石结构的固溶体，对环境中重金属的迁移转化和分布分配产生极大的影响。到目前为止，有关该固溶体系列的研究，以对结晶过程的理论计算与实验为主，而对溶解过程的实验研究非常缺乏；此外，在文献中还存在许多互相矛盾的结论。所以，本项目拟通过沉淀/溶解实验，确定含锰、镉、锌、钴、镍、铅等的方解石族矿物固溶体系列形成的条件及其稳定存在的pH值范围，并求得它们的溶度积和吉布斯生成自由能等热力学参数，作出其溶解过程的Lippmann图、Roozeboom图和分配系数图；同时对含重金属方解石族矿物固溶体系列在水环境中的溶解作用及其稳定性进行详细的研究，了解固溶体－水溶液作用过程中反应路径以及矿物表面组分与结构的变化，更好地掌握重金属在自然界中的迁移转化与分布分配规律。

The Ca2+ sites in the calcite lattices can accept many divalent cations, e.g., Mn2+, Cd2+, Zn2+, Co2+, Ni2+ and Pb2+, to form a series of heavy metal-bearing calcite-structured solid solutions in the nature, which plays a very important role in the transportation and transformation of these heavy metals in the environment. Until now, most of the researches focus on the theoretical calculation and experiment of the crystallization process of these solid solutions. Very few works have been made on their dissolution, and many contradictory conclusions can be found in literature. In the present research, therefore, the forming condition and the pH stability range of some solid solutions of calcite group minerals, containing Mn, Cd, Zn, Co, Ni and Pb, will be firstly determined through precipitation/dissolution experiments. Based on the obtained experimental data, the thermodynamic parameters, such as the solubility products and Gibbs free energies of formation of these solid solutions of calcite group minerals, will be calculated, and the Lippmann diagram, the Roozeboom diagram and the distribution coefficient diagram will be also generalized for the mineral-water interaction. Simultaneously, the dissolution and stability of the heavy metal-bearing solid solutions of calcite group minerals in water is to be studied in detail in order to understand the reaction path and compositional evolution of the solid solution and the aqueous solution and to recognize the variation of the surface composition and structure of the solids in solid solution-aqueous solution (SS-AS) systems. The research results can better clarify the transportation, transformation, distribution and participation characteristics of Mn, Cd, Zn, Co, Ni and Pb in the natural environment.