氟硅酸钾滴定法测定粗制氟化钠中二氧化硅

Determination of silicon dioxide in crude sodium fluoride by potassium fluosilicate titrimetric method with microwave digestion

采用硝酸-氢氟酸混合酸为消解溶剂,通过微波消解技术对粗制氟化钠进行快速消解,并用氟硅酸钾滴定法测定其二氧化硅含量。选择饱和氯化钾溶液替代固体氯化钾作为沉淀剂,考察了消解酸体系、饱和氯化钾溶液用量、沉淀温度、沉淀放置时间、共存元素干扰及指示剂选择等条件对测定结果的影响并进行优化。确定了最优测试条件:以8 mL硝酸+2 mL氢氟酸为消解溶剂,以8 mL饱和氯化钾溶液为沉淀剂,控制沉淀温度为20~25℃、沉淀放置时间为15 min,选择50 g/L氯化钾-50%乙醇溶液洗涤沉淀,采用溴麝香草酚蓝-酚红指示剂。该方法应用于回收粗制氟化钠中二氧化硅含量的测定可大幅度缩短分解试样的时间,有效降低检测成本,回收率为99.15%~100.63%,相对标准偏差(RSD,n=8)小于1%,与传统高温碱熔法测定结果相符,方法的准确度和精密度较好。

A rapid microwave digestion technology for the determination of silicon dioxide in crude sodium fluoride by potassium fluorosilicate titrimetric method with HNO3 and HF mixed acid as the digestion agent was studied.Saturated potassium chloride solution was selected to instead of solid potassium chloride as precipitant,and the effect of digestion acid system,saturated potassium chloride dosage,precipitation temperature,precipitation time,interference of coexisting elements and selection of indicators on the determination were investigated and optimized.The optimal test condition was determined that the precipitate was filtrated and washed with 50 g/L potassium chloride-50%ethanol solution after placing for 15 min and the precipitation temperature was controlled at 20~25℃with 8 mL nitric acid+2 mL hydrofluoric acid as digestion solvent and 8 mL saturated potassium chloride solution as the precipitant.The color of the endpoint of the titration changed obviously by using bromothymol blue and phenol red as a mixed indicator.This method was applied to the determination of the silicon dioxide content in the recovered crude sodium fluoride products,which could greatly shorten the time to decompose the sample,and effectively reduce the detection cost.The recovery rate was within the range of 99.15%~100.63%and the relative standard deviation(RSD,n=8)was less than 1%.The results were consistent with those obtained by traditional high-temperature alkali fusion method.The method showed high accuracy and precision.