Acid oxidative pressure leaching is a cost-effective way for recovering gold from refractory gold ores such as gold-bearing pyrite, yet our knowledge of the dissolution, crystallization, and phase transformation during pressure leaching is still controversial. This is partially due to the lack of thermodynamic data and in situ studies of the leaching process. Here, we combine thermodynamic modelling and in situ powder X-ray diffraction (PXRD) to investigate mineralogical phase changes during oxidation of pyrite. The polyhedron method has been utilised to estimate the standard Gibbs free energy of formation ($∆G_f^o$) and enthalpy of formation ($∆H_f^o$) of 31 sulphate minerals from 25 °C to 300 °C. The calculated thermodynamic data for the sulphate minerals agree well with the literature, with an average relative error of 0.23% for both $∆G_f^o$ and $∆H_f^o$ demonstrating the reliability of the polyhedron method. Some new thermodynamic data for the mineral phases at elevated temperature was calculated and used to construct the Eh-pH diagrams for the Fe-S-H₂O system at 225 °C, which were used to predict phase transformations and chemical reactions during oxidation of pyrite. Based on the analysis of thermodynamic diagrams, the formation of basic ferric sulphate (BFS: Fe(OH)SO₄) is favoured at stronger acidic and higher solution redox potential conditions, while hematite and FeSO₄∙H₂O occur at low solution redox potential conditions. These predictions agreed with the results from laboratory-based in situ PXRD experiments, in which the mineralogical phase transformations were studied during acid pressure treatment of pyrite in a capillary. The influence of initial concentration of ferric ions on the change of mineral phase was revealed. The results confirmed the formation of FeSO₄∙H₂O and Fe(OH)SO₄ phases during the heating (24–225 °C) and annealing stages. These phases may passivate pyrite surface and hence slow down further pyrite oxidation but were re-dissolved during the annealing and/or cooling stages, depending on the initial concentration of ferric ions.

酸氧化加压浸出是从含金黄铁矿等难处理金矿石中回收金的一种经济有效的方法，但我们对加压浸出过程中的溶解、结晶和相变的了解仍然存在争议。这部分是由于缺乏热力学数据和浸出过程的原位研究。在这里，我们结合热力学建模和原位粉末 X 射线衍射 (PXRD) 来研究黄铁矿氧化过程中的矿物相变。多面体方法已被用于估计标准吉布斯形成自由能（$∆G_F^o$) 和生成焓 ($∆H_F^o$) 从 25 °C 到 300 °C 的 31 种硫酸盐矿物。硫酸盐矿物的计算热力学数据与文献吻合良好，两者的平均相对误差均为 0.23%$∆G_F^o$和$∆H_F^o$证明多面体方法的可靠性。计算了高温下矿物相的一些新热力学数据，并用于构建 225 °C 下 Fe-SH ₂ O 系统的 Eh-pH 图，用于预测黄铁矿氧化过程中的相变和化学反应。根据热力学图分析，碱性硫酸铁 (BFS: Fe( OH )SO ₄ ) 在强酸性和高溶液氧化还原电势条件下有利于形成，而赤铁矿和 FeSO ₄ ∙ H ₂O发生在低溶液氧化还原电势条件下。这些预测与基于实验室的原位 PXRD 实验的结果一致，其中研究了毛细管中黄铁矿酸压处理过程中的矿物相变。揭示了铁离子初始浓度对矿物相变化的影响。结果证实在加热 (24–225 °C) 和退火阶段形成了 FeSO ₄ ∙H ₂ O 和 Fe( OH )SO _4相。这些相可能会钝化黄铁矿表面，从而减缓黄铁矿的进一步氧化，但会在退火和/或冷却阶段重新溶解，具体取决于铁离子的初始浓度。