海洋地质与环境重点实验室知识库

   深海稀土，指深海盆地中富含稀土元素的沉积物，是继多金属结核、富钴结壳及多金属硫化物之后被发现的第四种深海金属矿产，具有巨大的资源潜力。目前，我国针对深海稀土资源的调查和探测技术研究十分薄弱，缺乏完备的能够实时探测深海沉积物中稀土元素的技术手段，无法从深海沉积物中准确探测到稀土元素。因此，需要发展一种水下稀土探测技术，以实现深海稀土的原位、快速探测。激光诱导击穿光谱（Laser induced breakdown spectroscopy，LIBS）是一种有效的水下元素探测手段，具有原位、实时、连续、非接触等独特优势，近年逐渐应用到水下元素分析中。根据稀土元素自身特性，本论文提出了一种深海稀土探测新方法，即将深海沉积物中的稀土元素通过无机酸浸出，而后利用LIBS的水下分析能力对深海沉积物浸出液中的离子态稀土元素进行探测。如此，通过简单的化学浸出过程就能够实现深海富稀土沉积物中多个稀土元素的同时、快速检测和定量分析。

本论文探究了深海富稀土沉积物中稀土元素的溶出特性，证明了LIBS具有深海原位稀土元素探测的潜能，同时证实了利用LIBS结合多变量回归分析对深海沉积物中稀土元素进行检测和评价的可行性，为实现LIBS深海稀土探测提供技术与理论支持。主要工作如下：

（1）深海富稀土沉积物作为新兴矿产资源，备受关注。为实现深海LIBS探测，根据稀土元素易溶出的特性，本论文对中印度洋洋盆S024、S025、S028三个站点的深海富稀土沉积物进行了浸出实验，分析了不同无机酸种类和浓度、液固比及时间对稀土元素浸出的影响，以获得最佳浸出条件，达到富集稀土元素的目的。通过对比各浸出液中稀土元素的浸出率，得出深海富稀土沉积物中稀土元素的最佳浸出条件，即HNO₃浓度1-1.5 mol·L^-1、液固比2:1、浸出时间5 min。

（2）元素谱峰的归属是光谱探测的基础。在对浸出液中稀土元素定量分析之前，本论文通过将浸出液的LIBS光谱，与纯稀土溶液的LIBS光谱和LIBS标准光谱数据库（National Institute of Standards and Technology，NIST）比对进行稀土元素的谱峰归属，共获得11条稀土元素特征谱线。为获得质量更高的LIBS光谱，本论文对LIBS探测参数进行优化，获得浸出液中稀土元素探测和定量分析的最佳参数，即300 ns延时、25 mJ激光能量。

（3）实现深海富稀土沉积物中稀土元素的定量分析是本论文的最终目的。在最佳探测参数下，对所有浸出液进行LIBS探测，所得光谱经平均处理、波长位移差分算法（Wavelength artificial shift subtraction，WASS）校正后进行定量分析。为提高光谱定量的可靠性，本论文对比了单变量回归（Univariate regression，UVR）和偏最小二乘法（Partial least squares，PLS）两种定量分析方法。分析结果表明，PLS较UVR能够获得更好的回归系数（R²），更适合沉积物中稀土元素的定量分析。

      Deep-sea rare earth refers to the sediments rich in rare earth elements in deep-sea basins. It is the fourth deep-sea metal mineral discovered after polymetallic nodules, cobalt-rich crusts and polymetallic sulfides, and has great resource potential. At present, the research on the investigation and detection technology of deep-sea rare earth resources in China is very weak. There is a lack of complete technical means to detect rare earth elements in deep-sea sediments in real time, and rare earth elements cannot be accurately detected from deep-sea sediments. Therefore, it is necessary to develop an underwater rare earth detection technology to achieve in-situ and rapid detection of deep-sea rare earth. Laser induced breakdown spectroscopy (LIBS) is an effective method for underwater element detection. It has unique advantages such as in-situ, real-time, continuous and non-contact, and has been gradually applied to underwater element analysis in recent years. According to the characteristics of rare earth elements, this paper proposes a new method for deep-sea rare earth detection. The rare earth elements in deep-sea sediments are leached by inorganic acid, and then the ionic rare earth elements in the leaching solution of deep-sea sediments are detected by LIBS underwater analysis ability. In this way, simultaneous, rapid detection and quantitative analysis of multiple rare earth elements in deep-sea rare earth-rich sediments can be achieved through a simple chemical leaching process.

This paper explores the dissolution characteristics of rare earth elements in deep-sea rare earth-rich sediments, proves that LIBS has the potential of deep-sea in-situ rare earth element detection, and confirms the feasibility of using LIBS combined with multivariate regression analysis to detect and evaluate rare earth elements in deep-sea sediments. It provides technical and theoretical support for the realization of LIBS deep-sea rare earth detection.The main work is as follows:

(1) As an emerging mineral resource, deep-sea rare earth-rich sediments have attracted much attention. In order to achieve deep-sea LIBS detection, according to the characteristics of easy dissolution of rare earth elements, this paper carried out leaching experiments on deep-sea rare earth-rich sediments at three sites of S024, S025 and S028 in the Central Indian Ocean Basin. The effects of different inorganic acid types and concentrations, liquid-solid ratio and time on the leaching of rare earth elements were analyzed to obtain the best leaching conditions and achieve the purpose of enriching rare earth elements. By comparing the leaching rate of rare earth elements in each leaching solution, the optimum leaching conditions of rare earth elements in deep-sea rare earth-rich sediments were obtained, that is, HNO₃ concentration 1-1.5 mol·L^-1, liquid-solid ratio 2:1, leaching time 5min.

(2) The attribution of element spectral peaks is the basis of spectral detection. Before the quantitative analysis of rare earth elements in the leaching solution, the LIBS spectrum of the leaching solution was compared with the LIBS spectrum of the pure rare earth solution and the LIBS standard spectral database (NIST) to assign the spectral peaks of rare earth elements. A total of 11 characteristic spectral lines of rare earth elements were obtained. In order to obtain a higher quality LIBS spectrum, this paper optimizes the LIBS detection parameters to obtain the best parameters for the detection and quantitative analysis of rare earth elements in the leaching solution, that is, 300 ns delay and 25 mJ laser energy.

(3) The ultimate goal of this paper is to realize the quantitative analysis of rare earth elements in deep-sea rare earth-rich sediments. Under the optimal detection parameters, LIBS detection was performed on all leachates, and the obtained spectra were quantitatively analyzed after average processing and wavelength shift difference algorithm (WASS) correction. In order to improve the reliability of spectral quantification, this paper compares two quantitative analysis methods: univariate regression (UVR) and partial least squares (PLS). The analysis results show that PLS can obtain better regression coefficient (R²) than UVR, which is more suitable for the quantitative analysis of rare earth elements in sediments.

第1章 绪论 1

1.1  选题背景与意义 1

1.2  本论文的研究内容及章节安排 5

第2章 激光诱导击穿光谱技术及发展应用现状 7

2.1 激光诱导击穿光谱技术的基本原理及发展历程 7

2.1.1  激光诱导击穿光谱技术的基本原理 7

2.1.2  激光诱导击穿光谱技术的发展历程 10

2.1.3  激光诱导击穿光谱技术的定量分析原理 11

2.2  激光诱导击穿光谱在深海中的应用 14

2.3  激光诱导击穿光谱在稀土元素中的应用 15

第3章 深海沉积物中稀土元素溶出特性研究 19

3.1 深海沉积物中的稀土元素赋存特征 19

3.2  样品与方法 21

3.2.1  样品来源及信息 21

3.2.2  样品元素测定 22

3.2.3  浸出过程及浸出率的计算 24

3.3  结果与讨论 25

3.3.1  不同酸种类对稀土元素浸出的影响 25

3.3.2  不同酸浓度对稀土元素浸出的影响 26

3.3.3  不同液固比对稀土元素浸出的影响 29

3.3.4  不同浸出时间对稀土元素浸出的影响 29

3.4  小结 34

第4章 稀土元素的激光诱导击穿光谱探测方法研究 35

4.1  前言 35

4.2  激光诱导击穿光谱探测方法 36

4.2.1  稀土元素在激光诱导击穿光谱中的识别 36

4.2.2  激光诱导击穿光谱探测参数优化 39

4.2.3  激光诱导击穿光谱的采集 40

4.2.4  激光诱导击穿光谱的处理 41

4.2.5  激光诱导击穿光谱的定量分析 42

4.3  结果与讨论 43

4.3.1  激光诱导击穿光谱的单变量定量分析 43

4.3.2  激光诱导击穿光谱的偏最小二乘定量分析 45

4.4 小结 47

第5章 结论与展望 48

5.1 结论 48

5.2  下一步工作计划 48

参考文献 50

附录 深海富稀土沉积物中稀土元素、有价金属和放射性元素的浸出率 57

致  谢 62

作者简历及攻读学位期间发表的学术论文与其他相关学术成果 6