磷灰石族矿物固溶体的溶解热力学及其对有毒微量元素在固液体系中分配的影响

Apatite group mineral is an ideal environmental mineral for the removal of heavy metals from wastewater and contaminated soils because of its high sorption capacity for heavy metals, low water solubility, high stability under reducing and oxidizing conditions, availability, and low cost. In the present research program, the forming condition and the pH stability range of some common apatite solid solutions containing toxic trace elements will be firstly determined through precipitation/dissolution experiments. Based on the obtained experimental data, the thermodynamical parameters, such as the solubility products and free energies of formation of these apatite solid solutions, will be calculated, and Lippmann diagram, Roozeboom diagram and the distribution coefficient diagram will be also generalized for the mineral-water interaction. Simultaneously, the dissolution and stability of the apatite solid solutions 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 understand the surface composition and structure of the solid solutions in solid solution-aqueous solution （SS-AS）systems. The research results will be helpful in understanding the transportation, transformation and distribution characteristics of the toxic trace elements including arsenic, lead, cadmium, fluorine etc. The data will be also helpful to evaluate the long-term environmental effects of the chemical stabilization of the wastes containing toxic trace elements through the formation of solid solutions.

磷灰石族矿物，由于其对多种重金属具有广泛的容纳性和吸附固定作用、低溶解度、在不同氧化还原条件下的高稳定性和价格低廉，从而成为一种理想的环境矿物材料。本项目拟通过沉淀/溶解实验，确定几种常见的含有毒微量元素的磷灰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，并求得这些磷灰石族矿物固溶体系列的基本热力学参数，如它们的溶度积和生成自由能，作出其溶解过程的Lippmann图、Roozeboom图和分配系数图；同时对不同磷灰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，了解磷灰石族矿物固溶体和水溶液在相互作用过程中的反应路径与演变，以及矿物表面化学组分与结构在固溶体-水溶液作用过程中的变化，更好地掌握砷、铅、镉、氟等有毒微量元素在自然界中的迁移、转化与分布的规律，同时预测含有毒微量元素废物的化学固定过程中形成的各种固溶体对环境影响的长期效应。

磷灰石族矿物，由于其对多种重金属具有广泛的容纳性和吸附固定作用、低溶解度、在不同条件下的高稳定性和价格低廉，从而成为一种理想的环境矿物材料。本项目通过实验，确定常见的含有毒微量元素的磷灰石族矿物固溶体形成的条件及其稳定存在的pH值范围，并求得其基本热力学参数，如溶度积（Ksp）、生成自由能（ΔGfo）等。(Pb,Ca)5(PO4)3OH固溶体的Ksp随XPb升高从10-58.38下降为10-80.77；Guggenheim系数为a0=-1.16和a1=1.18；呈现含Pb较高的固相与含Ca较高的液相处于平衡状态。(Pb,Ca)5(PO4)3F的Ksp随XPb升高从10-62.07下降为10-76.99。(Cd,Ca)5(PO4)3OH的Ksp随XCd升高从10-57.65下降为10-64.62；Guggenheim系数a0=-1.33和a1=0.45；呈现含Cd较高的固相与含Cd较低的液相处于平衡状态。(Cd,Ca)5(PO4)3F的Ksp随XCd升高从10-58.22下降为10-59.17，然后又逐渐升高至10-56.89。对于(Zn,Ca)5(PO4)3OH，当XZn=0.00~0.08时，Ksp从10-57.75下降为10-58.59；当XZn=0.08~0.16时，Ksp从10-58.59升高到10-56.63。Ca2Pb3[(As,P)O4]3Cl的Ksp随XAs升高从10-70.14升高至10-66.46。Ca5[(As,P)O4]3Cl的Ksp随XAs升高从10-57.89升高至10-51.70。Ca5[(As,P)O4]3OH的Ksp随XAs升高从10-53.28逐渐升高至10-40.86；Guggenheim系数为a0=-17.8；XAs较低的固相，在水环境中亦可导致AsO43-的浓度的显著升高。Ca5[(V,P)O4]3OH的Ksp随XV升高从10-56.64降低至10-69.26。Ca5(PO4)3(F,OH)的Ksp随XF升高从10-58.71升高至10-57.42。Ca5(PO4)3(Cl,OH)的Ksp随XCl升高从10-55.66降低至10-57.89。Pb5(PO4)3(Cl,OH)的Ksp随XCl升高从10-80.77升高至10-78.31。研究结果有助于更好地掌握砷、铅、镉、氟等有毒微量元素在环境中的迁移、转化与分布的规律。

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