Pyrite (FeS₂) is a typical container of Pt in ores of magmatic and hydrothermal origin and in some carbonrich ores of sedimentary-diagenetic origin. Knowledge of the state of Pt disseminated in the matrix of pyrite, including local atomic environment (type of atoms in the nearest and distant coordination shells, coordination numbers, interatomic distances) and oxidation state, is necessary for physical-chemical modeling of platinum group element mineralization and for the improvement of Pt ore extraction and processing technologies. Here we report results of an investigation of local atomic structure of synthetic Pt-bearing pyrites by means of X-ray absorption spectroscopy (XAS). Synthesis experiments, performed at 580° and 590°C in a Pt-saturated system by means of salt-flux method, yielded crystals of pyrite with concentrations of Pt up to 4 wt %. Scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) showed that the distribution of Pt within the pyrite grains is of zonal character, but within the distinct zones Pt is distributed homogeneously. Negative correlation between the concentrations of Pt and Fe was observed in the synthesized pyrite grains. The slope of the correlation line corresponds to the formation of the solid solution in the Pt-Fe-S system and/or to the formation of PtS₂. The XAS experiments revealed the existence of two forms of Pt in pyrite. The main form is the solid solution Pt(IV), which isomorphically substitutes for Fe. The Pt-S distance in pyrite is ~0.1 Å longer than that of Fe-S in pure pyrite. The distortion of the pyrite crystal structure disappears at R >2.5 Å. The second Pt-rich form was identified by means of high-resolution transmission electron microscopy (HRTEM) as nanosized inclusions of PtS₂. Heating experiments with in situ registration of X-ray absorption spectra resulted in partial decomposition (dissolution) of PtS₂ nanosized inclusions with the formation of the solid solution (Fe_1–xPt_x)S₂. Therefore, the PtS₂ nanosized particles can be considered as a quench product. Our data demonstrate that both Pt solid solution and PtS₂ nanosized inclusions (at high Pt content) can exist in natural Pt-bearing pyrites.

中文翻译：

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用合成晶体的X射线吸收光谱研究硫铁矿中铂的状态

硫铁矿（FeS ₂）是在岩浆和热液成因的矿石中以及在沉积成岩成因的一些富碳矿石中的典型Pt容器。对于铂族元素的物理化学建模，必须了解在黄铁矿基质中散布的Pt状态，包括局部原子环境（最近和相近的配位壳中的原子类型，配位数，原子间距离）和氧化态。矿化和改善Pt矿石的提取和加工技术。在这里，我们报告通过X射线吸收光谱法（XAS）研究合成的含Pt硫铁矿的局部原子结构的结果。借助于盐通量法，在Pt饱和系统中于580°和590°C下进行的合成实验，生成的Pt浓度最高为4 wt％的黄铁矿晶体。扫描电子显微镜（SEM）和电子探针显微分析（EPMA）表明，Pt在黄铁矿晶粒内的分布具有带状特征，但在不同的区域内Pt分布均匀。在合成的黄铁矿晶粒中，Pt和Fe的浓度之间呈负相关。相关线的斜率对应于Pt-Fe-S系统中固溶体的形成和/或PtS的形成₂。XAS实验表明黄铁矿中存在两种形式的Pt。主要形式是固溶体Pt（IV），它同构地替代了Fe。黄铁矿中的Pt-S距离比纯黄铁矿中的Fe-S距离长约0.1Å。黄铁矿晶体结构的畸变在R> 2.5Å时消失。第二种富Pt形式通过高分辨率透射电子显微镜（HRTEM）鉴定为PtS _2的纳米尺寸包裹体。X射线吸收光谱原位记录的加热实验导致PtS ₂纳米夹杂物部分分解（溶解）并形成固溶体（Fe _1–x Pt _x）S ₂。因此，PtS ₂纳米尺寸的颗粒可被视为淬火产物。我们的数据表明，Pt固溶体和PtS ₂纳米夹杂物（高Pt含量）都可以存在于天然的含Pt黄铁矿中。