Determination of manganese and phosphorus in ferromanganese
WANG Yu-tong1, WANG Jian-yong*2
1. Sichuan University of Science and Engineering, College of Chemical Engineering, Zigong 643000, China; 2. Sichuan Dongfang Boiler Group Co., Ltd., Zigong 643000, China
Abstract：The content of manganese and phosphorus in ferromanganese was the main index for classification. The traditional methods for the determination of manganese and phosphorus in ferromanganese were trivalent manganese titration and molybdenum blue spectrophotometry. However, the determination process was tedious and time-consuming. The sample was dissolved with nitric acid-hydrofluoric acid-perchloric acid. Hydrogen peroxide was added to reduce manganese dioxide to manganese (II) to prepare the mother solution. The content of manganese and phosphorus in ferromanganese was determined by EDTA titration and phosphorus-bismuth-molybdenum blue spectrophotometry, respectively. The step-by-step determination method of manganese and phosphorus in ferromanganese with one-time sample dissolution was established. The determination conditions of manganese were optimized. The results showed that the addition of triethanolamine-potassium sodium tartrate solution could mask iron, copper, aluminum and titanium in the test solution. The certified reference material of ferromanganese was used for testing. It was found that the determination results were consistent with the certified values when methyl thymol blue was used as the indicator. Moreover, the color changed from blue to light red at endpoint, which was easily observed. 30mL of absolute ethanol and 25mL of hot water (about 80℃) were added to solve the problem of indicator ossification. The interference and elimination method of arsenic and residual silicon in the determination of phosphorus were also discussed. The results showed that the interference of arsenic could be eliminated by adding sodium thiosulfate-sodium sulfite solution, while interference of residual silicon could be eliminated by adding potassium sodium tartrate. The contents of manganese and phosphorus in ferromanganese samples were determined according to the experimental method. The relative standard deviations (RSDs, n=8) of the results was less than 0.30% and 4.0%, respectively. The proposed method was applied for the determination of manganese and phosphorus in certified reference materials of ferromanganese. The absolute value of relative error was less than 0.25% and 4.0%, respectively.
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