DENG Junhua, XU Qiang, TIAN Huijie, KANG Dehua, YANG Jie
To address the corrosion issue of platinum-gold crucible during the fusion sample preparation of ferroniobium, the effects of sample particle size, oxidant composition and dosage, and a stepwise pre-oxidation procedure were investigated. The results indicated that when the sample particle size was controlled at 0.074 mm, the fusion time could be reduced by 10 min compared to the sample particle size of 0.096 mm. A novel composite oxidant system of Li2CO3-LiOH-KNO3 (mass ratio of 12∶20∶5) was employed. This system leveraged the alkaline fusion by LiOH and the assisted fusion from CO2 release during Li2CO3 decomposition, while utilizing the mild oxidation characteristics of KNO3 to replace the traditional Na2O2/BaO2, significantly enhancing the reaction controllability. The interference from Br with the determination of 0.20% Al could be completely eliminated under the following experimental conditions: the fusion temperature of 1 100 ℃, 1.0 mL of LiBr solution, and a fusion time of 20 min. Based on these findings, a three-stage pre-oxidation method suitable for programmable fully automatic electric fusion furnaces was developed. In this method, the commercially available Li2B4O7 crucible was used. The mass ratio of sample (0.25 g) to Li2B4O7 and composite oxidant was controlled. After gradient pre-oxidation at 500-750 ℃, the sample was fused at 1 100 ℃. This approach not only completely avoided the corrosion risk of platinum-gold crucible, but also ensured the homogeneous formation of glass fusion beads. The calibration curves were established using standard reference materials, primary standard substances, and standard solutions of ferroniobium. The analysis method for simultaneous determination of eleven major and minor components (including Nb, Ta, Si, Al, P, Mn, Co, Cr, Ti, Fe and Sn) in ferroniobium by X-ray fluorescence spectrometry (XRF) was established. The linear correlation coefficients of calibration curves in this method were all not less than 0.999 5. One synthetic ferroniobium sample was determined according to the experimental method. The relative standard deviations (RSD, n=8) of determination results for Nb, Ta, Si, Al, P, Mn, Co, Cr, Ti, Fe and Sn were between 0.14% and 2.9%. One actual production sample of ferroniobium was selected for the comparison of this method and other methods as well as standard addition recovery tests. The results indicated that the determination values of Nb, Ta, Si, Al, P, Mn, Ti and Sn were consistent in two methods. The spiked recoveries of Fe, Cr and Co were between 101% and 110%.
