硅钼蓝分光光度法测定氟化稀土中二氧化硅

氟化稀土是一种用途广泛的材料,其中二氧化硅的含量是衡量产品品质的一个关键指标,直接影响生产合金的工艺和产品的质量。实验采用碳酸钠-硼酸混合熔剂(m_碳酸钠:m_硼酸=4:1)熔融试样,经盐酸酸化,加入0.4 mL硫酸(1+5)控制显色体系的pH≈1,正硅酸与钼酸铵沸水浴保温时间为3～5 s时形成硅钼杂多酸,用草酸-硫酸混合酸破坏磷、砷等干扰元素,抗坏血酸还原硅钼杂多酸为硅钼蓝,建立了光度法测定氟化稀土中二氧化硅含量的方法。试验表明,显色液中二氧化硅质量浓度在0.04～2.0 μg/mL范围内符合比尔定律,方法中二氧化硅的检出限和测定下限分别为0.002 8%和0.010%(质量分数)。方法用于3个氟化稀土实际样品中二氧化硅量的测定,结果的相对标准偏差(RSD,n=10)为2.3%～5.2%;测定值与电感耦合等离子体原子发射光谱法(ICP-AES)的测定结果一致。

Determination of silicon dioxide in rare earth fluoride by silicomolybdic blue spectrophotometry

The rare earth fluoride was a kind of widely used materials. The content of silicon dioxide in rare earth fluoride was a key index to measure the quality of product, which directly influenced on the alloy production process and product quality. The sample was fused with sodium carbonate-boric acid mixed flux with mass ratio of 4:1. After acidification by hydrochloric acid, the pH of sample solution was controlled at about 1 by adding 0.4 mL of sulfuric acid (1+5). The orthosilicic acid reacted with ammonium molybdate in boiling water bath for 3-5 s to form silicon-molybdenum heteropoly acid. The interference elements such as phosphorus and arsenic were destroyed by adding oxalic acid-sulfuric acid mixture. The silicon-molybdenum heteropoly acid was reduced to silicomolybdic blue by ascorbic acid. The determination method of silicon dioxide in rare earth fluorides by spectrophotometry was established. The results showed that Beer’s law was obeyed for the mass concentration of silicon dioxide in range of 0.04-2.0 μg/mL. The detection limit and low limit of determination for silicon dioxide was 0.002 8% and 0.010% (mass fraction), respectively. The proposed method was applied to the determination of silicon dioxide in three actual samples of rare earth fluoride. The relative standard deviations (RSD, n=10) were between 2.3% and 5.2%. The results were consistent with those obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES).