Determination of High Content of Molybdenum in Molybdenum Ore by Emission Spectrometry with Solid Sampling Technique

The majority of current molybdenum ore analysis techniques use absorbance, gravimetric methods, ICP-MS, ICP-OES, XRF, etc., which are primarily based on liquid injection, with a lengthy analytical procedure, complex steps, and a measurable range of 0.01%-5.17%^[16]. The joint technologies of EPMA, SEM, and X-ray spectroscopy are more expensive, and the results may not be reproducible^[18-21]. Compared with the above methods, AC-Arc atomic emission spectrometry (Arc-AES), which does not call for the use of acids and bases, has the potential to be applied to the analysis of molybdenum ore and molybdenum powder with a high content of Mo over 5%.

To improve the current analytical techniques for determining high content of molybdenum in molybdenum ore.

The mixed sample was loaded into the lower electrode after being ground at 2400Hz for 30min with the different sample-to-buffer ratio in a 5mL crucible. Two drops of a 2% mass fraction sucrose-ethanol solution were added and dried at 70℃ for 1h. The samples were mounted on an AES-8000 direct-reading atomic emission spectrometer using the vertical electrode method. The internal reference method was used to fit the quadratic curve in logarithmic coordinates by subtracting the background spectral lines of the analyzed elements and the internal reference elements.　　The experiments were conducted by choosing the internal reference element types and spectral lines, selecting the Mo spectral lines, deciding the sample-to-buffer ratio, optimizing the current loading procedure, setting the spectral uptake time, and other conditions. A set of national-level reference materials and national-level synthetic silicate spectral analysis reference materials were used for calibration. The relative standard deviation and logarithmic deviation were utilized for quality control.

(1) The analytical line pair is chosen to be Mo 277.54nm/Ge 326.9494nm. The uniformity of internal reference elements is ensured by the excessive addition of germanium dioxide. Mo 277.54nm and Ge 326.9494nm evaporation curves exhibit good consistency when GBW07142 is used as the sample (Fig.1). (2) The sample-to-buffer ratio is selected as 1∶2. It is discovered that the evaporation behavior is significantly improved when it reaches 1∶2; simply increasing the buffer, is not conducive to the analysis of actual samples. (3) Primary current is 4A for 5s, secondary current is 15A for 30s, and the total interception exposure time is 35s. The results show that the intensity of Mo and Ge greatly increases before 30s and slows down after 35s (Fig.2). (4) The reference series components are shown in Table 1 with the content range between 500 to 500800μg/g. The reference curve equation is y=−0.077x²+1.3077x+1.2725, with a coefficient of determination (R²) of 0.999 (Fig. E.1）.　　The detection limit of Mo in this method is 27.38μg/g, which is slightly higher than that of alkali fusion-inductively coupled plasma spectrometry (0.002%)^[9] and X-ray fluorescence spectrometry (0.0026%)^[16]. The RSD ranges from 3.28% to 8.30%, and the RE ranges from −0.43% to 0.73% (Table 2). The results are consistent with the reference values, with significant precision and accuracy, which meets the requirements (△lgC≤0.05, RSD≤10%) listed in Specification of Multi-Purpose Regional Geochemical Survey (DZ/T 0258—2014).

This method can be employed to determine the high Mo content in molybdenum ore and molybdenum powder without dilution. Moreover, it is suitable for a wider determination range with the upper limit rising to 50%. It can solve possible problems, such as large sample demand, large chemical reagent use, cumbersome operation and contamination in other analytical methods.