Thermodynamics and crystal chemistry of copper arsenates

矿床和矿点的氧化带可以是自然形成的，也可以是人为作用形成的。在这两种情况下，它们构成了自然过程的一个窗口，这些过程形成和塑造了地球表面附近的矿物，并决定了风化原生矿物周围的矿物，元素和生物群的命运。在这个建议中，我计划把重点放在砷酸铜矿物上，这是一组在许多氧化带中遇到的非常多变的矿物。它们能够固定或释放铜、砷和其他元素，如Pb、Zn或Se。在拟议的工作中，我们将确定端元和固溶体的铜砷酸盐矿物（chalcophyllite，liroconite，strashimirite，tyrolite，parnauite，geminite，和euchroite）的热力学性质的酸溶液（生成焓）和松弛（熵）量热法的组合。所选固溶体的混合参数将通过量热法或溶解度研究得出，并用于构建显示固溶体和水相之间相互作用性质的李普曼图。计算出的溶解度间隙将与天然固溶体的组成（由电子探针测定）进行严格比较。我们将开展实地工作，收集砷酸铜矿物和共存的水溶液在现场，并使用这些解决方案的组成，以达到研究阶段的热力学性质的独立值。在拟议工作的最后阶段，热力学结果和已知的砷酸铜晶体学模型将结合成一个数学模型，预测所有砷酸铜矿物的热力学性质，基于能量分配到矿物中的单个结构块（多面体）。

Oxidation zones of ore deposits and ore occurrences can originate naturally or by a maninduced action. In either case, they constitute a window in the natural processes which form and shape minerals near the Earth¿s surface and determine the fate of minerals, elements, and biota around the weathering primary minerals. In this proposal, I am planning to focus on copper arsenate minerals, an astonishingly variable group of minerals encountered in many oxidation zones. They are capable of immobilizing or releasing copper, arsenic, and other elements, such as Pb, Zn, or Se. Within the proposed work, we will determine thermodynamic properties of endmembers and solid solutions of copper arsenate minerals (chalcophyllite, liroconite, strashimirite, tyrolite, parnauite, geminite, and euchroite) by a combination of acid-solution (enthalpy of formation) and relaxation (entropy) calorimetry. The mixing parameters for selected solid solutions will be derived by calorimetry or solubility studies and used to construct Lippmann diagrams that show the nature of the interaction between a solid solution and an aqueous phase. The calculated miscibility gaps will be critically compared to the composition of natural solid solutions (determined by electron microprobe). We will carry out field work, collect copper arsenate minerals and co-existing aqueous solutions in the field, and use the composition of these solutions to arrive at independent values of thermodynamic properties of the phases studied. In the final phases of the proposed work, the thermodynamic results andthe known crystallographic models for the copper arsenates will be combined into a mathematical model that predicts the thermodynamic properties of all copper arsenate minerals, based on the assignment of energies to the individual structural blocks (polyhedra) in the minerals.