Determination of ultra-low volatile mercury concentrations in sulfur-rich gases and liquids.
Determination of ultra-low volatile mercury concentrations in sulfur-rich gases and liquids.
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DOI：
10.1016/j.talanta.2019.02.070
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发表时间：
2019-07
期刊：
影响因子：
6.1
通讯作者：
C. Brombach;T. Pichler
中科院分区：
文献类型：
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作者：
C. Brombach;T. Pichler
测定各种天然液体（即地下水、热液流体、酸性矿井排水、海底地下水排放等）和气体（即火山和热液排放物、烟道气、天然气、填埋气等）中的汞（Hg）浓度存在障碍，因为许多此类样品中存在H2S。传统的金捕集器捕集汞的方法由于被H2S“中毒”和冷蒸汽原子荧光光谱法（CV-AFS）测定汞的问题而达到了极限。由于这些样品类型中的汞浓度较低，通常需要收集超过20 L的大量液体或气体，这使得运输到实验室变得困难。考虑到这一点，我们开发了一种便携式方法，用于从富含H2S的气体和液体中收集汞。该方法使用了一个撞击装置，一个碱性陷阱后面跟着两个高锰酸钾-硫酸陷阱。高锰酸钾（KMnO4）将单质汞蒸气氧化为Hg2+， Hg2+保留在KMnO4溶液中，因此可以用CV-AFS分析。因此，不是25 L的样品，只有几mL必须运送到实验室。这种方法的一个可能的警告是，自然产生的气体通常是几种不同气体的混合物，如H2、CH4、so2和H2S，它们可以与KMnO4发生反应，从而消耗KMnO4。研究了不同浓度的气体化合物对KMnO4捕集汞的影响。氢和ch4不产生干扰，而so2与KMnO4发生反应。当第一个kmno4陷阱的氧化能力被SO2耗尽时，汞被困在第二个kmno4陷阱中，作为一个安全陷阱。两种kmno4捕集器对汞的回收率均达到99.5 %。然而，当系统中加入H2S后，汞的回收率下降了近50% %。这一观察结果归因于当kmno4 -陷阱的氧化能力被消耗时，陷阱中形成硫化汞（HgS）。氯化亚锡（SnCl2）不能还原HgS，这是CV-AFS检测所必需的。通过在两个kmno4捕集器前添加一个含有还原剂硼氢化钠（NaBH4）的碱性捕集器来克服这个问题。在这个陷阱中，H2S转化为S2-，而S2-没有到达kmno4陷阱，同时nabh4阻止了Hg氧化成Hg2+，然后沉淀成HgS。当体积为1000 mL的H2S通过冲击柱时，Hg的回收率为98.05 ± 3.6 % （n = 3）。该方法的现场试验验证了H2S对热液气中汞的捕获和最终测定的影响。使用碱性陷阱，我们测定了汞浓度为358 ng m−3Hg，而没有碱性陷阱，只有101 ng m−3Hg。因此，没有碱性陷阱的设置导致实际汞浓度低估了71.8 %，并证实了碱性陷阱克服H2S干扰的必要性。
Determining mercury (Hg) concentrations in a wide range of naturally occurring liquids (i.e., groundwater, hydrothermal fluids, acid mine drainage, submarine groundwater discharge, etc.) and gases, (i.e., volcanic and hydrothermal emissions, flue gas, natural gas, land fill gas, etc.) has obstacles due to the presence of H2S in many of such samples. The classical approach of trapping Hg on gold traps comes up against its limits due to “poisoning” of the traps by H2S and problems for its determination by cold vapor atomic fluorescence spectrometry (CV-AFS). Due to low concentrations of Hg in these sample types it is often necessary to collect large amounts of liquid or gas in excess of 20 L, which makes transport to the laboratory difficult. With this in mind we developed a portable method for the collection of Hg from gases and liquids rich in H2S.The method uses an impinger set-up with an alkaline trap followed by two potassium permanganate - sulfuric acid traps. The potassium permanganate (KMnO4) oxidizes elemental Hg vapor to Hg2+, which remains in the KMnO4solution and thus can be analyzed by CV-AFS. Thus, rather than 25 L of sample, only a few mL have to be transported to the laboratory. A possible caveat of this approach is that naturally occurring gases are generally a mixture of several different gases, such as H2, CH4, SO2and H2S, which can react with and thus consume KMnO4. The influence of various gas compounds at different concentrations were tested for their effect on the trapping of Hg by KMnO4. Hydrogen and CH4did not cause any interference, while SO2did react with the KMnO4. When the oxidizing capacity in the first KMnO4-trap was depleted due to SO2, Hg was trapped in the second KMnO4-trap, which acted as a safety trap. Good recoveries of 99.5 % were achieved for the Hg collected in both KMnO4-traps. Nevertheless, when H2S was introduced into the system, Hg recovery dropped by almost 50 %. This observation was attributed to the formation of mercury sulfide (HgS) in the trap when the oxidation capacity of the KMnO4-trap was consumed. HgS cannot be reduced by stannous chloride (SnCl2), which is necessary for detection by CV-AFS. The problem was overcome by adding an alkaline trap with the reductant sodium borohydride (NaBH4) in front of the two KMnO4-traps. In this trap H2S was converted to S2-, which does not reach the KMnO4-trap while at the same time NaBH4prevented the oxidation of Hg to Hg2+followed by precipitation as HgS. Good recoveries of 98.05 ± 3.6 % (n = 3) were obtained for Hg when a volume of 1000 mL H2S was passed through the impinger train.Field testing of the method verified the effect of H2S on the trapping and ultimately the determination of Hg in the hydrothermal gas. With the alkaline trap we determined a Hg concentration of 358 ng m−3Hg, while without the alkaline trap only 101 ng m−3Hg. Thus, the set-up without the alkaline trap led to an underestimation of the real Hg concentration by 71.8 % and confirmed the necessity of an alkaline trap to overcome the interference of H2S.