The kaolin sample is hardly decomposed.During the determination of silicon dioxide in kaolin by silicon molybdenum blue spectrophotometry,there are some problems such as easy polymerization of silicic acid in acid solution and bad stability of silicon molybdenum yellow,etc.The sample was firstly wetted with little ethanol.Then the kaolin sample was decomposed by fusion using sodium hydroxide-sodium peroxide as mixed flux.After fusion decomposing of sample,a large-volume container was used to avoid the polymerization of silicon by hydrochloric acid inverse acidification.5 mL of anhydrous ethanol and ammonium molybdate solution were successively added into 0.10-0.20 mol/L hydrochloric acid system to improve the stability of silicon molybdenum yellow.Then oxalic acid-sulfuric acid mixture was added to eliminate the interference of phosphorus and arsenic.After reducing silicon molybdenum yellow to silicon molybdenum blue,the solution was determined at 660 nm.Consequently,the determination method of silicon dioxide content in kaolin by silicon molybdenum blue spectrophotometry was established.The results indicated that Beer's law was obeyed for silicon dioxide with mass concentration in range of 1.00-10.00 μg/mL.The correlation coefficient was 1.000 and the detection limit of silicon dioxide was 0.033 μg/mL.The interference tests of main component (aluminum oxide) and impurity components (ironic oxide,titanium dioxide,calcium oxide,magnesium oxide,potassium oxide,sodium oxide,phosphorus and arsenic) in kaolin were conducted.The results showed that these components had no interference with the determination.The proposed method was applied for the determination of silicon dioxide in two certified reference materials of kaolin,and the found results were basically consistent with the certified values.The relative standard deviations (RSD,n=6) were 0.29％ and 0.36％,respectively.The content of silicon dioxide in six actual samples of kaolin was determined according to the experimental method,and the found results were basically consistent with those obtained by secondary hydrochloric acid dehydration gravimetric method in national standard method (GB/T 14563-2008).%高岭土样品较难分解,在采用硅钼蓝分光光度法对其中二氧化硅进行测定时,存在硅酸在酸性溶液中易聚合,硅钼黄的稳定性较差等问题.实验采用先加入少许乙醇润湿样品,再加入氢氧化钠-过氧化钠混合熔剂进行熔融的方法,实现了对高岭土样品的分解.将样品熔融分解后,选用体积较大的容器以盐酸逆酸化法以避免硅的聚合,在0.10～0.20 mol/L盐酸体系中,采用先加入5 mL无水乙醇,再加入钼酸铵溶液的方法提高了硅钼黄的稳定性,随后加入草酸-硫酸混合酸以消除磷、砷的干扰,用硫酸亚铁铵将硅钼黄还原成硅钼蓝,于波长660nm处测定,建立了硅钼蓝分光光度法测定高岭土中二氧化硅含量的方法.结果表明,显色液中二氧化硅质量浓度在1.00～10.00 μg/mL范围内符合比尔定律,相关系数为1.000,方法中二氧化硅的检出限为0.033 μg/mL.对高岭土中的主要组分三氧化二铝及杂质组分三氧化二铁、二氧化钛、氧化钙、氧化镁、氧化钾、氧化钠、砷、磷等进行了干扰试验,结果表明,这些组分均不干扰测定.实验方法用于2个高岭土标准物质中二氧化硅的测定,测定值与认定值基本相符,结果的相对标准偏差(RSD,n=6)分别为0.29％和0.36％.按照实验方法测定6个高岭土实际样品中的二氧化硅,测定值与采用国家标准方法GB/T 14563-2008中二次盐酸脱水重量法的测定结果基本一致.
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