The role of sulfur in palladium transport and fractionation from platinum by hydrothermal fluids

Excel spreadsheets with data reproduced from all the tables and figures from the article "The role of sulfur in palladium transport and fractionation from platinum by hydrothermal fluids" by Laskar et al.
The solubility of palladium sulfide (PdS(s)) has been measured in H2S/HS– aqueous solutions across wide ranges of sulfur concentrations (0.5–1.2 molal) and pH (5–8) at temperatures from 50 to 300 °C and pressures from 90 to 600 bar, using a hydrothermal flexible-cell reactor allowing controlled fluid injection and sampling. Combined with thermodynamic modeling and analysis of available literature data, our results demonstrate that palladium tetrahydrosulfide, PdII(HS)42–, is the dominant complex in sulfide-rich moderate-temperature hydrothermal fluids. The equilibrium constants of PdS(s) dissolution reaction, PdS(s) + 3 H2S0(aq) = Pd(HS)42– + 2 H+ (Ks4,Pd), generated in this study can be described by the function log10Ks4,Pd = (196.4±60.0) – (11384±3567)/T(K) – (71.24±19.52) × log10T(K), valid over the temperature range 25–300 °C and from saturated vapor pressure to 600 bar. Our results, combined with recent analogous PtS(s) solubility data, enabled the derivation of a self-consistent set of thermodynamic properties of Pd(HS)42– and Pt(HS)42– in the framework of the HKF model. Solubility predictions of PdS(s) using these properties yield maximum solubility values of 1 ppb Pd, as the tetrahydrosulfide complex, in H2S-bearing hydrothermal fluids (>0.01 m S) at moderate temperatures (50–350 °C) and near-neutral pH (6–7), whereas chloride complexes are predominant at acidic pH (<4). The Pd/Pt atomic ratio in typical H2S-bearing hydrothermal fluids at 300 °C in equilibrium with PdS(s) and PtS(s) varies from >104 at pH <2 to 10–2 at pH>3, corresponding to the change from chloride- to sulfide-dominated speciation for both metals. However, the absolute solubilities of both chloride and sulfide complexes are too small over the whole pH range to significantly contribute to Pd vs. Pt fractionations observed in hydrothermal environments. Among different factors that may lead to such fractionations, the role of polysulfide sulfur species, including trisulfur radical ions, should be considered in future studies.

本数据集为复刻自Laskar等人发表的论文《热液流体中硫在钯从铂中迁移与分馏的作用》（The role of sulfur in palladium transport and fractionation from platinum by hydrothermal fluids）中所有表格与图版数据的Excel电子表格。

本研究采用可实现流体可控注入与取样的热液柔性池反应器，在温度50~300℃、压力90~600巴（bar）的条件下，于硫浓度范围0.5~1.2质量摩尔浓度（molal）、pH 5~8的H2S/HS–水溶液中测定了硫化钯（PdS(s)）的溶解度。结合热力学建模与现有文献数据分析，本研究结果证实，在富硫中低温热液流体中，四氢硫化钯(II)（PdII(HS)42–）为主要的钯络合物。

本研究得到的PdS(s)溶解反应：PdS(s) + 3 H2S0(aq) = Pd(HS)42– + 2 H+的平衡常数（Ks4,Pd），可通过公式log10Ks4,Pd = (196.4±60.0) – (11384±3567)/T(K) – (71.24±19.52) × log10T(K) 进行描述，该公式适用于25~300℃的温度区间以及饱和蒸气压至600巴（bar）的压力范围。

结合近期发布的同类PtS(s)溶解度数据，本研究推导得到了HKF热力学模型（Helgeson-Kirkham-Flowers thermodynamic model）框架下Pd(HS)42–与Pt(HS)42–的一套自洽热力学性质。

基于上述热力学性质开展的PdS(s)溶解度预测结果显示：在中低温（50~350℃）、近中性pH（6~7）且含H2S（硫浓度>0.01质量摩尔浓度（molal））的热液流体中，以四氢硫化钯络合物形式存在的钯最大溶解度可达1 ppb（parts per billion）；而在酸性pH（<4）条件下，氯络合物为钯的主要存在形态。

在300℃下与PdS(s)和PtS(s)达到平衡的典型含H2S热液流体中，Pd/Pt原子比随pH变化：在pH<2时大于10⁴，在pH>3时降至10⁻²，这对应两种金属的络合形态从氯络合物主导转变为硫络合物主导。

不过，在整个pH范围内，氯络合物与硫络合物的绝对溶解度均极低，不足以对热液环境中观测到的Pd与Pt分馏现象产生显著贡献。

在可能引发该分馏的诸多因素中，多硫化物硫物种（包括三硫自由基离子）的作用应在未来研究中予以考虑。