Abstract：In the past, the content of phosphorus and silicon dioxide in iron ore were determined separately by molybdenum blue spectrophotometry. When the phosphorus molybdenum blue spectrophotometry was used, the determination results of phosphorus were often inaccurate due to the interference by vanadium and arsenic. As a result, the sample should be retreated before determination. With bottom of iron crucible covered by graphite, the iron ore was melted at high temperature with sodium carbonate-boric acid mixture as flux. After complete decomposition, the content of phosphorus and silicon dioxide in iron ore sample was determined by bismuth phosphorus molybdenum blue spectrophotometry and silicon molybdenum blue spectrophotometry, respectively. Therefore, the combined determination of phosphorus and silicon dioxide in iron ore by molybdenum blue spectrophotometry was realized. The interference test indicated that vanadium (V) was reduced to vanadium (III) by graphite during the melting at high temperature, which eliminated the interference of vanadium with the determination of phosphorus. 15 mg of sodium thiosulfate solution was added into the coloring solution to reduce arsenic (V) to arsenic (III), which eliminated the interference of arsenic with the determination of phosphorus. Beer′s law was obeyed for phosphorus with mass concentration in the range of 0-3μg/mL. The linear correlation coefficient of calibration curve was 0.9999. The apparent molar absorptivity was 2.242×104 L·mol-1·cm-1. Beer′s law was obeyed for silicon dioxide with mass concentration in the range of 0-5μg/mL. The linear correlation coefficient of calibration curve was 0.9995. The apparent molar absorptivity was 9.342×103 L·mol-1·cm-1. The detection limit of phosphorus and silicon dioxide in this method was 0.0026μg/mL and 0.0081μg/mL, respectively. The contents of phosphorus and silicon dioxide in six certified reference materials of iron ore were determined according to the experimental method. The relative standard deviations (RSD, n=8) of determination results for phosphorus were less than 5%, and the relative error was less than 2%. The RSDs (n=8) of determination results for silicon dioxide were less than 2%, and the relative error was less than 1.5%. The contents of phosphorus and silicon dioxide in five iron ore samples were determined according to the experimental method. The RSDs (n=8) was less than 7% and 1% for phosphorus and silicon dioxide, respectively. The determination results of phosphorus and silicon dioxide were consistent with those obtained by inductively coupled plasma atomic emission spectrometry.
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