Determinations of Zr, Hf and Nb Contents in Soil Samples by
Laser-Induced Breakdown Spectroscopy (LIBS)
ZHANG Peng-peng1, 2, XU Jin-li1, 2*, HU Meng-ying1, 2, ZHANG Ling-huo1, 2, BAI Jin-feng1, 2, ZHANG Qin1, 2*
1. Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang 065000, China
2. Key Laboratory of Geochemical Exploration, Ministry of Natural Resources, Langfang 065000, China
Abstract：Zirconium, hafnium and niobium are important elements in analysing multi-objective geochemical samples. It is difficult to completely remove these high field strength elements in traditional wet pretreatment, resulting in low results. Moreover, traditional wet digestion has many disadvantages, such as high acid and alkali, long pretreatment process and environmental pollution. LIBS has a unique advantage in analysing geochemical samples, especially for those elements that are not completely digested under conventional conditions. In this study, the zirconium, hafnium and niobium elements in soil samples were quantitatively analyzed by laser-induced breakdown spectroscopy. Firstly, the output energy of the laser, the longer time of acquisition by the spectrometer and the diameter of the laser spot were optimized. Comparing the accuracy of the laser output energy from 0.0 to 4.4 mJ in determining zirconium, hafnium and niobium in soil samples, when 1.6mj is selected, the best experimental results can be obtained. Secondly, the influence of the extended collection time of the spectrometer on the determination of zirconium, hafnium and niobium in soil samples is analyzed, and the results show that 0.5 μs is the best acquisition delay time condition. Finally, the measurement results are obtained by comparing different laser spot diameters, and 50 μm is selected, the stability of the measurement is the best. At the same time, this experiment also carried out a comparative experimental study from the measurement mode and sample preparation pressure. The results show that the stability of the LIBS signal and the accuracy of quantitative analysis is the best when using laser-induced breakdown spectroscopy to measure Zr, Hf and Nb in soil samples under the sample preparation pressure of 2 000 kN and dynamic mode. Under the optimal experimental conditions (laser output energy 1.6 mJ, spectrometer acquisition time 0.5 ms and laser spot diameter 50 μ m). The dynamic model was used to detect Zr, Hf and Nb in 9 national first-class reference materials. The measured values are consistent with the recommended values. The precision of 3 national first-class reference materials is less than 11%, which can meet the analysis requirements of geochemical samples. Based on the above conditions, this paper established a laser-induced breakdown spectroscopy (LIBS) method to analyze the content of Zr, Hf and Nb in soil samples, which solved the problems of incomplete digestion and low determination results of Zr, Hf and Nb in wet digestion. It has high analysis efficiency, simple operation and no pollution. It also provides a choice for the development of solid sampling technology.
Key words：Zirconium; Hafnium and niobium; Laser-induced breakdown spectroscopy; Soil
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