A new method to remove hydrogen sulfide from geothermal fluids during well operation was tested in situ at a geothermal site in Vienna (Austria). For this purpose, ferric iron was added either as granulated iron hydroxide or as FeCl3 solution into a reaction vessel containing the thermal water directly removed from the wells. From the container, the water would be pumped through a particle filter. Physicochemical parameters as well as sulfide were measured constantly over time before and after the filter. It was found that the sulfide was fully removed from the water by both iron additives. While the addition of FeCl3 led first to the formation of black iron(II) sulfide (FeS), which subsequently oxidized in presence of oxygen to Fe(III) hydroxide, no visible change of the granulated iron hydroxide was observed. The reaction time was longer when using the Fe(III) hydroxide additive as compared to the FeCl3 (completed in less than 20 min) but could be enhanced by increasing the amount of added particles. In all experiments the pH was constantly rising during the reaction from about 6.3 to 7.5, which was explained by loss of protons due to purging out of the gaseous H2S. The redox value, which was measured over time, remained rather constant after addition of granulated iron hydroxide (about −350 mV), but strongly increased from −350 mV to −50 mV after adding the FeCl3 suggesting a strong electron-consuming reaction. This can be explained by a two-step reaction: first, the Fe(III) was reduced to Fe(II) by oxidation of either sulfide or thiosulfate to sulfate. Afterward, the Fe(II) oxidized again by dissolved oxygen forming orange Fe(III) hydroxides. The application of the investigated method during operation of geothermal wells could prevent H2S-induced corrosion and would eliminate the toxic effects of this gas.

中文翻译：

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Fe（III）基添加剂从地热流体中去除硫化氢

在维也纳（奥地利）的一个地热站点现场测试了一种在井作业期间从地热流体中去除硫化氢的新方法。为此目的，将三价铁以粒状氢氧化铁或三氯化铁溶液的形式加入到反应容器中，该反应容器中含有从井中直接除去的热水。从容器中，水将被泵送通过颗粒过滤器。在过滤器前后，随着时间不断地测量理化参数以及硫化物。发现两种铁添加剂都已将硫化物从水中完全去除。虽然首先加入FeCl3导致形成黑色硫化铁（IIS），然后在氧气存在下将其氧化成氢氧化铁（III），但未观察到粒状氢氧化铁的可见变化。与使用FeCl3相比，使用Fe（III）氢氧化物添加剂的反应时间更长（在不到20分钟的时间内完成），但是可以通过增加添加的颗粒数量来延长反应时间。在所有实验中，pH在反应过程中一直不断地从约6.3升高到7.5，这可以解释为由于从气态H2S中清除而导致的质子损失。随时间测量的氧化还原值在添加粒状氢氧化铁（约-350 mV）后保持相当恒定，但在添加FeCl3后从-350 mV强烈增加至-50 mV，表明强烈的电子消耗反应。这可以通过两步反应来解释：首先，通过将硫化物或硫代硫酸盐氧化为硫酸盐，将Fe（III）还原为Fe（II）。之后，Fe（II）再次被溶解的氧氧化，形成橙色的Fe（III）氢氧化物。