CaxCd1-xCO3固溶体在河流、湖泊等水体底泥锁定固化重金属镉中起着关键作用，但目前其对Cd2+离子的锁定与活化机制尚不清楚。这限制了人们认识碳酸盐型含镉沉积物在河流、湖泊等水体环境中的浓度水平和“源”/“汇”转化关系。本项目拟通过研究温度、水相组成及碳酸钙晶型等对CaxCd1-xCO3固溶体形成过程的影响，确定其形成机理；考察水体静态和动态条件下腐殖质、铁锰氧化物及新型有机污染物等对CaxCd1-xCO3固溶体-水溶液间的相平衡及相转移的影响，揭示各个相间Cd2+离子跨界面迁移与宿命归趋行为；在此基础上，从微观晶体结构出发建立热力学模型进行模拟预测，阐明CaxCd1-xCO3固溶体晶体结构与溶解度间的定量化构-效关系，从而在分子水平上找出CaxCd1-xCO3固溶体锁定与活化Cd2+离子的关键控制因素。本项目为利用天然和人工碳酸钙型矿石实现对镉长期而又安全地地下处置提供理论基础。

CaxCd1-xCO3 solid solution plays a key role in locking cadmium ion in complex water body of rivers and lakes, but the locking and activation mechanism of Cd2+ is unclear. This has limited the awareness of the concentration level and source/sink mechanism of carbonate bound form Cd sediments in these water environments. In order to determine the formation mechanism of CaxCd1-xCO3 solid solution, the effect of temperature, aqueous solution composition as well as the crystal type and crystal morphology of calcium carbonate on the generation process of CaxCd1-xCO3 solid solution will be first studied. Through the studies on the influences of humus, iron and manganese oxides and the persistent organic pollutants on the phase equilibrium and phase transformation for the CaxCd1-xCO3 solid solution-aqueous solution systems, the formation condition of CaxCd1-xCO3 solid solution will be elucidated. On this basis, within the framework of quasi-harmonic approach, the thermodynamic properties of the solid-solution(CaxCd1-xCO3) including the Gibbs free energy are systematically predicted, which can be combined with the phase diagram and thermodynamic data for thermodynamic modeling performed by means of CALPHAD(CALculation of PHAse Diagrams) approach. The quantitative relations between the material structures(including matrix and surface properties) and the solubility will be established, providing a valuable theoretical basis and technical support for predicting the mechanism of locking and activating Cd2+ by CaxCd1-xCO3 solid solution as well as the key control factors of locking Cd2+ at the molecular level. This project attempts to reveal the stability and the rule of migration and transformation of CaxCd1-xCO3 solid solution in aqueous solution, which will provide an important theoretical guidance for the treatment of the cadmium sediments in natural aquatic environment.