水合物赋存域孔隙水地化参数拉曼定量分析可行性研究

IOCAS-IR > 海洋地质与环境重点实验室

	水合物赋存域孔隙水地化参数拉曼定量分析可行性研究
	田陟贤
学位类型	博士
导师	阎军
	2015-05-19
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位专业	海洋地质
关键词	水合物孔隙水地化参数拉曼光谱定量分析
摘要	地球化学调查是确定海底天然气水合物存在与否、成分与结构、赋存状态和具体环境等信息的最有效手段，水合物赋存域沉积物孔隙水分析是其重要组成部分。传统沉积物孔隙水研究方法保真度低，调查结果存在巨大的探测误差和复杂的不确定性。拉曼光谱技术作为一种非侵入、非破坏、无试剂消耗的测试技术，可在极端环境下进行固体、液体、气体分子原位识别，并逐步向定量和定性分析同步进行发展。深海原位激光拉曼光谱技术虽尚处于探索和起步阶段，却为天然气水合物及其赋存域海洋沉积物孔隙水的研究提供了全新的思路和技术参考，使得获取高保真、高精度的孔隙水地化信息成为可能。基于此，本文对水合物赋存域沉积物孔隙水地化参数的激光拉曼光谱定量分析展开可行性实验研究。通过定量研究发现，液态水O-H伸缩振动谱带是多种振动模式的集成光谱，其形态和强度易受温度、盐分影响而变化，其低波数频带变化是由液态水氢键的缔合与破坏所致。温度对氢键的影响规律为：低温有助于氢键的缔合，而温度升高则会削弱氢键的作用并破坏水的结构。采用频移参数描述液态水伸缩振动拉曼峰的形变强度，讨论了频移参数与盐度之间的关系。实验分析结果表明，盐度越大，频移参数越大，伸缩振动峰形变越大。海水中常见离子对液态水OH伸缩振动谱带影响能力排序如下：SO₄^2-> CO₃^2-；I^- > Br^- > Cl^- > HCO₃^- > F^-；Sr²⁺ > Ca²⁺ > Mg²⁺；K⁺>Na⁺。而液态水弯曲振动频带对温度、压强和盐分条件的变化均不敏感，故本研究选择液态水在1635cm^-1附近的OH弯曲振动谱带（1300-2000cm⁻¹）作为定量分析的内标峰。基于内标定法的SO₄^2-拉曼光谱定量分析的可行性实验研究显示，该技术可用于SO₄^2-的定量探测并具有良好的精度。对采集自台湾西南冷泉活动区的孔隙水进行SO₄^2-浓度激光拉曼定量分析与离子色谱分析，发现两种方法得到的结果存在一定程度的误差。结合前人研究认为误差是由拉曼光谱中强烈的荧光背景影响所致，且荧光背景随孔隙水采集、暴露的时间增加而增强。使用“深海沉积物中水合物地球化学参数原位探测模拟系统”对CH₄溶液的原位激光拉曼定量分析同样具有良好的精度，因此将激光拉曼光谱技术应用于深海沉积物孔隙水甲烷浓度原位分析是可行的。使用该系统并以高纯度石英砂模拟沉积物，对CH₄在沉积物中溶解运移速率进行了半定量分析，为使用该系统开展进一步天然气水合物研究奠定了基础。探索了一种样品碱化辅助的孔隙水溶解无机碳拉曼定量分析方法，以溶解无机碳中拉曼活性最低、占比例最大的HCO₃^-为研究对象进行了可行性实验研究与分析。通过碱化处理将HCO₃^-转化为拉曼散射活性更强的CO₃^2-，有效降低了拉曼光谱系统对HCO₃^-的检出限。实验结果显示，该方法对与孔隙水相当的低浓度HCO₃^-溶液的定量分析具有良好的精度（相对误差<6.5%）。孔隙水硫化物在拉曼光谱曲线上表现为位于2550~2620cm⁻¹的明显拉曼重叠峰，包括H₂S的H-S伸缩峰（2592cm⁻¹）和HS⁻的H-S伸缩峰（2572cm⁻¹）。对基于内标定法的H₂S与HS⁻拉曼光谱定量分析进行了可行性研究，证实该技术可行且精度良好。H₂S与HS⁻作为一组共轭酸碱对，其浓度比和pH值呈函数关系。通过配制不同pH值的含硫化物溶液并进行拉曼光谱分析发现，这一关系在拉曼光谱上表现为特征拉曼重叠峰形态和H₂S、HS⁻分峰强度的规律性变化，即硫化物拉曼光谱参数与溶液pH值之间存在一定的耦合关系。基于谱峰分解和相关分析，提出了基于激光拉曼光谱技术的含硫化物孔隙水pH原位测定方法，可测定硫化物拉曼重叠峰可分辨情况下的孔隙水pH，在本研究中为6.11~8.32，涵盖了已知的绝大多数孔隙水pH值范围。
其他摘要	Geochemical methods are the most effective ways to indicate the occurrence of submarine gas hydrate and get the information about the composition and structure, occurrence state and environment of submarine gas hydrates. Marine sediment pore water of gas hydrate occurrence area is of great importance for it carries large quantities of geology and biogeochemistry information. It is difficult for traditional analysis methods to obtain high-fidelity pore water geochemical parameter data from retrieved samples. Laser Raman spectroscopy is capable of in situ molecular identification of solids, liquids, and gases and is well suited to extreme environments. The development of deep ocean Raman in situ spectrometer provide us new technical reference for the study of marine sediment pore water in gas hydrate occurrence regions. We conducted a feasibility study of quantitative analysis of sediment pore water parameters using laser Raman spectroscopy. It is reasonable to regard water as the internal standard for quantitative analysis of sediment pore water. Raman spectroscopy of liquid water can be divided into OH stretching vibration bands and OH bending vibration bands. The former is asymmetric and multi-mode superimposed, and is susceptible to salt and temperature. Skewing parameter was introduced to describe Raman spectroscopy distortion of water molecule stretching variation. The results show that the skewing parameter and distortion of OH stretching vibration bands increase with increasing salinity adding to the solutions. Effects of some common cations and anions in seawater on Raman spectra of water were analyzed, and effects of ions are in the following sequence: SO₄^2-> CO₃^2-, I^- > Br^- > Cl^- > HCO₃^- > F^-, Sr²⁺ > Ca²⁺ > Mg²⁺, K⁺>Na⁺. On the contrary, the OH bending vibration bands of liquid water is symmetric and stable. Therefore, OH bending band of water (1300-2000 cm⁻¹) is treated as the internal standard in this study for its stability. We study the quantitative analysis of the two important pore water geochemical composition SO₄^2- and CH₄ with Raman spectroscopy. The results show that the Raman spectroscopy quantitative techniques based on internal standard method can be used for quantitative analysis of SO₄^2- and CH₄ in aqueous solution with good accuracy. We propose here a sample alkalization aided Raman spectroscopy quantitative analysis method of DIC in sediment pore water. HCO₃^- is chosen as the study object for it takes the largest share and has the weakest Raman activity in all DIC species. The solution is alkalized and HCO₃^- is converted into CO₃^2- which is much moor Raman active. The Raman spectroscopy analysis detecting limit of HCO₃^- is decreased, and the result of quantitative analysis shows good accuracy (relative error<6.5%). Sulfide species in water have a relatively strong Raman signal, which often appears in the form of a characteristic overlapping peak between 2550~2620 cm⁻¹ and can be decomposed into HS⁻ at 2572cm⁻¹and H₂S at 2592cm⁻¹. In the present paper, quantitative analysis of H₂S and HS⁻ with Raman spectroscopy is proved practicable and the accuracy is good. The pH of pore water is an important influencing factor of the diagenetic processes. As H₂S and HS⁻ are conjugate acid-base pairs, sulfide species within pore water exist as a function of pH and their concentration ratio depend on pH. This relationship is also shown in the Raman spectrum. To formulate the pore water pH calculation, sulfide solutions with pH range from 6.11 to 13.05 were prepared and their Raman spectra were observed. It is verified that the morphology of overlapping peaks change regularly with pH values. This phenomenon provides us the possibility of measuring the pH of pore water in situ via Raman spectroscopy. Based on peaks decomposition and correlativity analysis, we propose here a novel in situ pH measuring method for sediment pore water containing sulfide. This method can be used to measure the pH of pore water when the overlapping peak of sulfide is resolvable. The application scope of this pH measuring method in this study is 6.11~8.32, which covers almost all pH value of marine sediment pore water already known.
学科领域	主要研究方向 ; 海洋地质与环境
文献类型	学位论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/22731
专题	海洋地质与环境重点实验室
作者单位	中国科学院海洋研究所
第一作者单位	中国科学院海洋研究所
推荐引用方式 GB/T 7714	田陟贤. 水合物赋存域孔隙水地化参数拉曼定量分析可行性研究[D]. 北京. 中国科学院研究生院,2015.

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