激光诱导击穿光谱技术快速探测煤灰中的重金属锌

煤灰的成分指的是煤中矿物质的完全燃烧，产生各种金属和非金属氧化物和盐，这是使用煤时的重要参数。煤被广泛用于生产和人民生活，作为重要的能源物质。大量来自燃煤燃烧的煤尘（煤灰）被释放到大气中并与大气中的各种物质相互作用而形成雾霾。煤灰中的金属氧化物和空气中的小液滴之间发生一系列物理化学反应，这导致了雾霾的形成。在实验中，采用激光诱导击穿光谱（LIBS）分析煤灰中的元素。实验样品由某钢铁公司提供，分为七个样品，并标上序号。样品分别加入蒸馏水和0.1‰，0.2‰，0.2％，0.4％，0.8％，1％硫酸锌溶液，分别用1～7号标记。为了获得更好的LIBS信号，样品被研磨为粉末状，并使用蒸馏水使硫酸锌与煤灰充分混合。通过使用压片机将煤灰压制成10 mm直径和10 mm厚的煤灰块。为获得准确的元素结果，X射线荧光光谱也被用作参考，并且原始样品不含锌元素。由于光谱分析和波长漂移现象的不确定性，因此实验中，分别选择了铁，钙，钛和铝四种高纯单质。在相同的实验条件下，将四条测量的元素谱线与NIST原子光谱数据库中相应的谱图比较。实验中的所有光谱根据波长差或偏移进行校正。此时，纯单质的元素谱线可以与样品的光谱对齐。当元素谱中的特征线与样品中的谱线对齐时，样品就可以被识别和确认。由于铝元素与目标元素具有相似的化学和物理性质，铝元素是煤灰和地壳中的主要元素之一，具有中等的光谱强度。因此将铝元素作为内标元素，运用内标校准方法来确定样品中锌的浓度。模拟含锌大气气溶胶是通过向煤灰中添加含锌元素来实现的。还有一些其他的金属元素，包括铁，钙，锰，钛和铝也被用来加入煤灰中，用以模拟大气气溶胶。两种方法的相对差异分别为1.78％，3.39％，5.17％，0.20％。造成差异的原因可能是由于光谱仪缺乏分辨率或背景噪声的影响，这是可能导致测量误差的原因之一。由于实验室条件的限制，无法确定基底是否会影响实验结果，这将在未来的实验中得到进一步的证实。实验拟合曲线测得煤灰中锌的线性相关系数为0.995 72，这表明可以通过粗略估算锌的激光强度来估计煤灰中的锌含量的实现。实验结果证明LIBS技术可用于煤灰中金属元素的快速检测，为基于锌含量的大气环境检测提供了一种新方法。在建立元素的校准曲线后，LIBS技术将来可以用来进行更快速，更准确的定量分析。

Rapid Detection of Zinc in Coal Ash by Laser Induced Breakdown Spectroscopy

The composition of coal ash refers to complete combustion of the minerals in the coal, producing a variety of metals and non-metallic oxides and salts, which is an important parameter when using coal. Coal has been widely used in the production and people’s life, as an important energy substance. A large amount of coal dust (coal ash) from coal combustion was released into the atmosphere and interacted with various substances in the atmosphere to form haze. A series of physico-chemical reactions take place between metal oxides in coal ash and small droplets in the air, which result in the formation of haze. In this study, laser induced breakdown spectroscopy (LIBS) was employed to analyze the elements in coal ash. The experimental samples were provided from a steel company, which was divided into seven parts. Distilled water and 0.1‰, 0.2‰, 0.2%, 0.4%, 0.8%, 1% zinc sulfate solution were added into samples, which were labeled with number 1～7 respectively. In order to obtain a better LIBS signal, the sample was powdered. The water in the solution was used to thoroughly mix zinc with coal ash. In the experiment, the coal ash was pressed into 10mm diameter and 10 mm thick coal ash blocks by using a tabletting machine. In order to get accurate elemental results, X-ray fluorescence spectroscopy were also employed for reference, and the original sample did not contain zinc. Due to the uncertainty of spectral analysis and wavelength shift phenomenon, qualitative analysis of element was inaccurate. To solve this problem, four kinds of high-purity elements including iron, calcium, titanium and aluminum were separately selected. Under the same experimental conditions, four measured elemental spectral lines were compared with the corresponding spectra in the NIST atomic spectral database. All the spectra in the experiment were corrected according to the wavelength difference or shift. At this point, the elemental spectrum of pure elements can be aligned with the samples’ spectrum. The samples then can be identified and confirmed when the characteristic line in the elemental spectrum is aligned with the spectrum in the samples. Because Al has similar chemical and physical property with target element, and Al is one of the major elements in coal ash and the crust, and has moderate spectral intensities. For quantitative analysis, the internal standard calibration method was used to determine the concentration of zinc in the samples. The results of simulating zinc-containing atmospheric aerosols were achieved by adding zinc to coal ash. Some other related metal elements, including iron, calcium, manganese, titanium and aluminum were also used to spike into coal ash to simulate atmospheric aerosols. The relative difference between the two methods is 1.78%, 3.39%, 5.17%, 0.20%. The reason for the difference may be due to the lack of resolution of the spectrometer or the impact of background noise, which could lead to the measurement error. Due to the limitations of laboratory conditions, we can’t be sure whether the influence of matrix will affect the experiment results, and which will be further confirmed by future experiments.The linear correlation coefficient of zinc in coal ash was determined to be 0.995 72, indicating that the rough estimation of zinc content can be achieved by the intensity of zinc in the spectrum. The experiment concluded that LIBS technology can be used for the rapid detection of metal elements in coal ash, and this work provides a novel method for the detection of atmospheric environment based on the content of zinc.After establishing the calibration curve of the elements, the LIBS technique can be used to conduct a rapid and accurate quantitative analysis in the future.