CaxCd1-xCO3固溶体多介质界面行为及其对自然水体Cd2+离子相变-锁定机制研究

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.

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。在国家自然科学基金21607176项目资助下，探究了温度、离子强度、pH、液相组成等对CaCO3晶体表界面Cd2+离子形成CaxCd1−xCO3固溶体过程的影响规律，考察了水体静态条件下腐殖质、壳聚糖等对CaxCd1xCO3固溶体-水溶液间的相平衡及相转移的影响，揭示了碳酸钙型含镉固溶体-水溶液相间Cd2+离子跨界面的迁移与宿命归趋行为；在矿化过程中，热力学稳定的碳酸钙(CaCO3)优先结合Ca2+离子和CO32离子成核，Cd2+离子进而在方解石(10ī4)界面上由静电吸附结合Ca2+离子和CO32离子形成CdxCa1−xCO3固溶体，进一步探究了CaxCd1−xCO3固溶体的晶体结构、固溶体成相模式、极限固溶度与固溶体组成之间的定量化关系，阐明了以CaCO3为基体的CaxCd1−xCO3固溶体形成机制；在此基础上，深入开展了天然矿物结构碳酸钙型上水石、麦管石、合成仿生的存在界面缺陷的方解石界面等离子锁定固化水体Cd2+离子的研究，从微观晶体结构出发建立热力学模型进行模拟预测，阐明了CaxCd1−xCO3固溶体对Cd2+离子的“锁定”与“活化”机制。.项目执行期间，发表研究论文13篇，其中SCI收录9篇，中文核心期刊3篇，申请国家发明专利3项，授权1项，申请国家软件著作权2项，培养硕士4名。获得湖南省第十五届青年化学化工奖、湖南林业师德模范、湖南省大学生“挑战杯”杰出工作者、优秀指导教师，入选湖南省青年骨干教师培养计划、长沙市杰出青年英才培养计划、长沙市工业科技特派员等。所取得的研究成果有望为利用天然和人工的碳酸钙型矿石屏障人为可控下加速Cd2+离子的沉降固着、防止Cd2+离子迁移转出从而实现对水体镉进行长期的地下处置提供理论依据，并创新性的将其应用于填埋类危险废物的稳定化固化处置过程，极大降低重金属危险废物的环境危害性，对重金属类危险废物的安全处理处置有着重要的意义。.