Electron probe microanalysis of the key metal beryllium

Abstract

As beryllium (Be) has been widely used in advanced technology, national defense, security systems, and other strategic emerging industries, it has become one of the key metals in the competition between countries. However, Be is an ultra-light metal element and its accurate in-situ analysis is a technical bottleneck in the geoscience field. Although secondary ion mass spectrometry (SIMS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) can be used to analyze Be, they are mainly used for the in-situ analysis of trace Be. Moreover, the analysis of Be is affected by the substrate effect, large analysis error, and lack of standard samples. Thus, the in-situ analysis of Be has a great impact on the research of the occurrence and metallogenic mechanism of Be. Electron probe microanalyzers (EPMA) have an obvious advantage in the analysis of the quantity of minerals. The in-situ analysis of Be may be performed in the configuration of a spectroscopic crystal with large mesh spacing. In this study, an electron probe microanalyzer (Shimadzu) equipped with a spectroscopic crystal (LAS300), was used to explore the analytical conditions of Be. Based on the analysis of a standard sample of metal Be, its analytical conditions of voltage and current were obtained. The peak interference and intensity of Be are discussed by the analysis of metal Be, beryl, bertrandite, hambergite, mengxianminte, bromellite, and other Be-bearing minerals, as well as pulse height analyzer (PHA) filtration. Using the above analysis conditions, the chemical compositions of the main Be-bearing minerals (bertrandite, phenakite, and beryl) were systematically and quantitatively analyzed. The results show that: (1) The proposed analysis conditions of Be are a voltage of 12 kV, considering the peak intensity and stability; the analytical current of the anhydrous Be minerals is between 100–200 nA; and the analytical current of hydrous Be minerals is between 50–100 nA. The PHA is selected to filter the higher-ordered X-rays of other heavy elements during the measurement, and the measured time is usually set between 50 and 100 s. (2) Before the analysis, the characteristic X-ray peak position of Be in Be-bearing minerals must be determined to choose the appropriate BG (+) and BG (−) and the same or similar Be-bearing minerals should be selected as standard samples. Based on the above conditions, the quantitative analysis of Be-bearing minerals can be performed well by EPMA. (3) The amount of Be-bearing minerals were analyzed to confirm the above conditions, which resulted in suitable contents of BeO in main Be-bearing minerals from Be resources. Bertrandite and phenakite from the volcanic rocks of Qingtian, Zhejiang Province contain 39.95wt%–43.15wt% and 45.33wt%–47.08wt% BeO, respectively. Beryl from the tungsten Be ore of Damingshan, Lin’an, Zhejiang Province, consists of 12.74wt%–13.75wt% BeO. (4) The technical difficulties of quantitatively analyzing Be arise from the fact that the 2S electrons from the outer layer of Be cannot transition to 1S to produce X-rays, which results in the flat-peak pattern phenomenon of characteristic X-ray, a peak shift, and weak peak intensity. In conclusion, it is feasible to use the above analytic conditions to quantitatively analyze Be-bearing minerals, which are not only of great practical significance to understanding the occurrence, metallogenic mechanism, and resource distribution of Be but also helpful in revealing the mineralogical and geochemical properties of Be.