Tungsten (VI) speciation in hydrothermal solutions is investigated through in-situ Raman spectroscopy coupled with the fused silica glass capillary technique at temperatures up to 400 °C. The effect of temperature, pH, chlorinity and carbonate speciation are evaluated in systems with highly soluble salts NaWO and NaWO. At all investigated temperatures, the tungstate ion WO (927 cm) is the only W species in solution at pH > 10. At a given pH, the presence of dissolved carbonates and chloride does not affect the tungsten speciation. Tungsten polymers remain stable up to 400 °C under acidic to circum-neutral pH conditions and total tungsten concentration above 0.01 mol⋅kg. Among the three observed polymers, namely [WO] (paratungstate-A, ∼960 cm), [WO] (tungstate-Y, ∼970 cm), and α-[HWO] (α-metatungstate, ∼990 cm), only the hepta- and dodeca-tungstate are stable at elevated temperature. Combined with revised literature data, these results allow the thermodynamic stability constants of these W polymers to be constrained, enabling quantitative predictions of their relative abundance at temperatures up to 300 °C. These predictions suggest that W polymerization occurs under hydrothermal conditions even at low W concentration (down to 10 mol·kg) under acidic conditions. These observations imply that the currently available geochemical models on W transport and deposition in deep and hot geological fluids need to be revised.

中文翻译：

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原位拉曼光谱揭示了高达 400°C 的热液中钨 (VI) 形态

通过原位拉曼光谱结合熔融石英玻璃毛细管技术，在高达 400 °C 的温度下研究热液中钨 (VI) 的形态。在具有高溶解度盐 NaWO 和 NaWO 的系统中评估温度、pH、氯度和碳酸盐形态的影响。在所有研究的温度下，在 pH > 10 的溶液中，钨酸根离子 WO (927 cm) 是唯一的 W 形态。在给定的 pH 值下，溶解的碳酸盐和氯化物的存在不会影响钨的形态。在酸性至中性 pH 条件下且总钨浓度高于 0.01 mol·kg 时，钨聚合物在高达 400 °C 的温度下仍保持稳定。在三种观察到的聚合物中，仅[WO]（仲钨酸盐-A，~960 cm）、[WO]（钨酸盐-Y，~970 cm）和α-[HWO]（α-偏钨酸盐，~990 cm）七钨酸盐和十二钨酸盐在高温下稳定。结合修订后的文献数据，这些结果允许限制这些 W 聚合物的热力学稳定常数，从而能够定量预测它们在高达 300 °C 的温度下的相对丰度。这些预测表明，即使在酸性条件下低浓度的钨（低至 10 mol·kg）下，钨聚合也会在水热条件下发生。这些观察结果意味着目前可用的关于深层热地质流体中钨传输和沉积的地球化学模型需要修改。