地质样品中黑碳的分离方法研究及在松辽白垩纪地层中的初步应用
发布时间:2018-05-29 11:01
本文选题:总有机碳 + 黑碳 ; 参考:《中国科学院研究生院(广州地球化学研究所)》2015年硕士论文
【摘要】:黑碳(BC)是生物质和化石燃料等不完全燃烧产生的含碳物质。黑碳在生物地球化学循环中有着非常重要的作用,也是全球碳循环中重要的源和汇。古老沉积物中黑碳的记录可以重建过去的火灾和陆地植被演化历史,也可以间接获得过去大气中氧气浓度。在前期工作的基础上,本文以古老地质样品为研究对象,首先对样品中总有机碳(TOC)的测定和黑碳的分离方法进行了研究与改进,然后使用改进后的方法对松辽盆地白垩纪地层中(以青山口组和嫩江组为例)的TOC和BC含量进行测定,对当时的火灾历史和古气候特征进行了初步的探讨。获得的主要认识和结论如下:1、总有机碳是土壤和沉积物等样品的重要指标,然而预处理方法对样品TOC值的最终测定会产生一定的影响。针对这个问题,本论文主要从酸处理方式、干燥过程等方面研究了预处理方法对不同类型样品的TOC含量和稳定碳同位素(δ13C值)测定的影响。研究结果显示:酸处理方式对TOC含量测定的影响很大,Ag杯和盐酸酸化/分离未去除残留酸液两组实验所测得TOC含量明显大于其他组。这种差异可能是样品酸处理过程中水溶性有机碳(DOC)的损失所造成的。对于δ13C测定来说,该两组实验所测得δ13C相对于其他组略微偏重。另外加热干燥和真空冷冻干燥方式测定的TOC含量和δ13C值没有明显的变化,表明了挥发性有机物对本次实验所选用样品的有机碳分析影响甚微。综合来看,对于含有较多DOC的现代样品来说,Ag杯法是比较好的选择;对于含DOC很少的古老地质样品来说,样品的预处理方法对样品的最终测定影响相对较小,可根据实验条件选择最方便快捷的方法。2、铬酸化学氧化法和热氧化法(CTO-375)是地质样品中黑碳的常用测定方法,但这两种方法都存在一些缺点,比如化学氧化法会把高成熟度的干酪根误判为黑碳,从而高估了黑碳的含量,而CTO-375方法也存在有机碳焦化的现象。针对这些问题,本文选择低成熟度的Ⅰ型和Ⅲ型干酪根作为基础样品,通过热模拟制备了两套不同成熟度的干酪根,然后以这两套样品为参考物,对传统铬酸氧化法分离BC和CTO-375热氧化法分离soot-BC进行了系统对比和优化,研究结果显示:(1)分离含有Ⅰ型干酪根的沉积物样品中的BC,干酪根成熟度低于1.25%时传统的铬酸氧化法可很好的去除干酪根,在成熟度0.38-0.89%时使用传统的铬酸氧化法处理氧化时间需要延长到120 h;而成熟度在0.89-1.25%时将氧化时间延长到300 h;成熟度高于1.25%时,该法具有一定的局限性。对于Ⅲ型干酪根来说,铬酸氧化法的去除效果较差,表明Ⅲ型干酪根含有部分抗氧化性的碳质组分。这种现象意味着Ⅲ型干酪根可能会对铬酸氧化法分离沉积物中黑碳造成较大的干扰。但总的来说对含有低成熟度Ⅲ型干酪根的样品,传统铬酸氧化法还是可以谨慎使用的;(2)针对成熟度高于1.25%的样品,从氧化剂浓度方面对传统铬酸氧化法进行优化,初步的结果表明提高氧化剂浓度可以有效地改善铬酸氧化法的效率;(3)使用CTO-375热氧化法分离沉积物中soot-BC时,干酪根对其并不造成影响,但其具体的处理方式有待进一步改进。3、采用改进的铬酸氧化法和常规CTO-375法对松辽盆地白垩纪嫩江组和青山口组样品中黑碳记录进行了研究,来重建这段时期松辽盆地的湖泊及周边区域内火灾的频次和规模以及火山喷发事件等。结果表明:(1)青山口组:桻一段的TOC和BC含量都非常低,可能是由于鸟河剖面位于整个松辽盆地湖泊的边缘,湖水较浅,有机质和黑碳都不利于保存;桻一段上部TOC组分中BC所占的比例由下至上逐渐升高,这可能是由于从青一段到青二段气候逐渐干旱导致。在青二段下部BC含量有一处大幅度升高,其升高的强度大于TOC增加的强度,推测该时间段有频繁火灾事件发生,且根据前人研究该段发现火山灰层,因此该时间段的火灾可能与频繁的火山活动有关。(2)嫩江组:根据嫩江组BC的记录,在嫩一中下部,BC的丰度升高,其升高的强度大于TOC增加的强度,推测该时间段有频繁火灾事件发生,且根据前人研究该段发现火山灰层,因此该时间段的火灾可能与频繁的火山活动有关。在嫩一段上部,TOC和BC的丰度都处于较低的水平,可能是由于嫩一段中部至上部,湖水逐渐变浅,相对更不利于有机质的保存。在嫩二段BC具有明显较高的含量,且波动范围很大,反映这一段存在明显强烈的火灾事件。而在同一时期,TOC的含量也很高,反映这段时间生物量非常大。另外由于海侵事件大量陆地上沉积的BC被带入湖泊中被沉积下来,且海侵使湖水变深,使得BC和TOC都很好的保存下来。至嫩二段中部,TOC和BC的丰度都有下降的趋势,可能该时期的气候逐渐干凉。嫩一段下部可能发生了小规模的剧烈大火事件。
[Abstract]:Black carbon (BC) is a carbon containing substance produced by incomplete combustion of biomass and fossil fuels. Black carbon plays a very important role in the biogeochemical cycle. It is also an important source and sink in the global carbon cycle. The record of black carbon in ancient sediments can reconstruct the history of the evolution of past fires and terrestrial vegetation, and can also be indirectly obtained in the past. The concentration of oxygen in the atmosphere. On the basis of the earlier work, this paper takes ancient geological samples as the research object. First, the determination of total organic carbon (TOC) and the method of black carbon separation are studied and improved. Then the improved method is used for the TOC and BC containing in the Cretaceous layer of the Songliao Basin (with the Qingshankou group and the Nenjiang group as an example). The main understanding and conclusions obtained are as follows: 1, total organic carbon is an important indicator of soil and sediment samples. However, the pretreatment method will have a certain effect on the final determination of the TOC value of the sample. The effects of pretreatment methods on the content of TOC and the determination of stable carbon isotopes (delta 13C values) of different types of samples were studied. The results showed that the effect of acid treatment on the determination of TOC content was great, and the content of TOC in the two groups of Ag cup and hydrochloric acid acidification / separation without removing residual acid solution was obviously greater than that of the others. This difference may be caused by the loss of water-soluble organic carbon (DOC) in the sample acid treatment. For the delta 13C determination, the two groups of experiments have measured slightly partial weight of the delta 13C relative to the other groups. In addition, the TOC content and delta 13C value determined by the heating drying and vacuum freeze drying methods have not changed significantly, indicating the volatile organic compounds. There is little influence on the organic carbon analysis of the samples selected in this experiment. For the modern samples containing more DOC, the Ag cup method is a better choice. For the old geological samples with little DOC, the pre treatment method of the sample is relatively small for the final determination of the sample, and it can be chosen most convenient according to the experimental conditions. Fast methods.2, chromic acid chemical oxidation and thermal oxidation (CTO-375) are common methods for determining black carbon in geological samples, but there are some shortcomings in these two methods. For example, chemical oxidation can misjudge the high maturity kerogen as black carbon, so that the content of black carbon is overestimated, and CTO-375 method also has the phenomenon of organic carbon coking. In order to solve these problems, two sets of kerogen with different maturity were prepared by thermal simulation with low maturity type I and type III kerogen as the base sample. Then the two sets of samples were used as reference materials to compare and optimize the separation of soot-BC by traditional chromic acid oxidation method BC and CTO-375 thermal oxidation method. The results showed that the results were obvious. (1) separation of BC in the sediment samples containing type I kerogen, and the traditional chromic acid oxidation method can remove the kerogen well when the maturity of kerogen is less than 1.25%, while the oxidation time of the traditional chromic acid oxidation process needs to be prolonged to 120 h when the maturity is 0.38-0.89%, while the maturity is extended to 300 h when the maturity is at 0.89-1.25%. When the maturity is higher than 1.25%, the method has some limitations. For the type III kerogen, the removal of chromic acid oxidation method is poor, indicating that type III kerogen contains some antioxidant carbon components. This phenomenon implies that type III kerogen may interfere with the black carbon in the sediment by chromic acid oxidation method. For samples containing low maturity type III type kerogen, traditional chromic acid oxidation method can be used carefully. (2) the traditional chromic acid oxidation process is optimized from the concentration of oxidant for the samples with higher maturity than 1.25%. The preliminary results show that improving the oxidizing agent concentration can effectively improve the efficiency of chromic acid oxidation process; (3) use C. When TO-375 thermal oxidation is used to separate soot-BC from the sediments, the kerogen does not affect it, but its specific treatment needs to be further improved by.3. The modified chromic acid oxidation method and the conventional CTO-375 method are used to study the black carbon record in the Cretaceous Nenjiang and Qingshankou formation samples of the Songliao Basin, to reconstruct the Songliao Basin during this period. The frequency and scale of fire in the lake and its surrounding area and volcanic eruption events show that: (1) the content of TOC and BC in the Qingshankou group is very low, maybe because the bird river section is located at the edge of the lake in the whole Songliao Basin, the lake water is shallow, the organic matter and the black carbon are not good for preservation, and the BC in the upper TOC component of the upper section is accounted for. The proportion of BC is gradually rising from the bottom to the top, which may be due to the gradual drought from the Qingyi to the green section. In the lower part of the two section of the Qing Dynasty, there is a large increase in the BC content in the lower part of the two section of the Qing Dynasty. The fire in the interval may be related to frequent volcanic activity. (2) Nenjiang group: according to the record of the Nenjiang group BC, the abundance of BC in the lower middle part of Nen is higher than that of TOC. It is suggested that there are frequent fire events in this period, and the fire possibility of this period is possible according to the discovery of the volcanic ash layer in this section. It is related to frequent volcanic activity. The abundance of TOC and BC at the upper part of the tender section is at a lower level, which may be due to the shallow water of the middle to the upper part of the tender one, which is relatively less conducive to the preservation of the organic matter. In the two part of the tender section, the BC has a significantly higher content and a wide range of fluctuations, reflecting the obvious and intense fire incident in this section. And in the same period, the content of TOC is very high, reflecting the very large biomass in this period. In addition, as a result of the transgression events, a large amount of land deposited on land has been deposited in the lake, and the transgression makes the lake water deep, so that both BC and TOC are well preserved. The abundances of TOC and BC have a downward trend in the middle part of the two tenderness, possibly the same. During the period, the climate gradually cooled down. A small and severe fire occurred in the lower part of the Nen.
【学位授予单位】:中国科学院研究生院(广州地球化学研究所)
【学位级别】:硕士
【学位授予年份】:2015
【分类号】:P595;P534.53
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