方解石在地壳中广泛分布，数量巨大，是最重要的碳酸盐矿物。方解石具有强大的杂质元素包容能力，可通过类质同象置换的方式固定大量有毒有害元素，如放射性元素铀及重金属元素铅、铬、砷等。因此，在自然条件下或通过人工诱导使有毒有害元素与方解石共沉淀，对污染环境修复具有重要作用，相关的研究和实践越来越受到关注。然而，方解石的化学活性较强，有可能在环境条件改变时发生溶解，并导致其中的有毒有害元素重新释放而造成二次污染。另一方面，磷灰石的溶度积很低，实验及野外调查证实，方解石在含磷条件下将转化为更稳定的羟基磷灰石，从方解石中释放出来的有毒有害元素也可能转移到羟基磷灰石中而被重新固定，但鲜有相关的研究报道。本项目拟通过实验合成和天然样品研究，对比羟基磷灰石与方解石对典型有毒有害元素的包容能力，查明其在方解石向羟基磷灰石转变过程中的归趋，其研究结果具有重要的科学价值和现实意义。

Calcite, the most important carbonate mineral, is in huge amount and widely distributed in the Earth’s Crust. Due to the high flexibility of calcite lattice, a lot of toxic and hazardous elements, such as U, Pb, Cr, As, et al., can be incorporated into calcite via isomorphous substitution. Thus, immobilization of toxic and hazardous elements via co-precipitation with calcite is more and more attractive in both scientific studies and environment remediation. However, because calcite is reactive, the toxic elements in calcite might be re-mobilized during the dissolution of calcite. On the other hand, apatite is much more insoluble than calcite, and experiments and field investigations have demonstrated that calcite can transform to hydroxyapatite in phosphate-bearing media. It is desirable that the toxic elements released from the dissolved calcite would be re-immobilized by hydroxyapatite during the phase transformation. However, the relevant investigation has rarely been reported. The current proposal is to (1)compare the incorporation capacity of selected toxic elements between calcite and hydrxyapatite,(2) reveal the fate of the toxic elements when calcite transforms to hydroxyapatite. The potential results will enhance our understanding on the behavior of toxic and hazardous elements in environment. Furthermore, it will provide useful information for the remediation of contaminated sites.