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用茜素胺酸钠一次甲基蓝为指示剂的硝酸钍滴定法已广泛应用于测定氟,还有锆盐滴定法等.这些方法虽简便,但终点都不很明显,钍又有放射性,污染环境.本文为了克服上述缺点,参阅了文献,进行一系列条件试验,拟定了在高氯酸中,氟与二氧化硅作用生成硅氟酸,蒸馏分离后,加入过量硝酸镧溶液沉淀氟离子,以氯乙酸作为加速沉淀剂.加入过量EDTA,以二甲酚橙为指示剂,用标准锌溶液反滴定过剩的EDTA,本法终点明显,快速、准确,测定氟的含量范围宽(4～100毫克氟),比常用的硝酸钍滴定法和锆盐滴定法优越.
Thorium nitrate titration with alizarin sodium primary methyl blue indicator has been widely used in the determination of fluoride, zirconium titration method, etc. Although these methods are simple, but the end is not very clear, thorium and radioactive, Pollution of the environment.In order to overcome the above shortcomings, this paper refers to the literature, conducted a series of conditional tests, in the preparation of perchloric acid, the role of fluorine and silica to generate hydrofluoric acid, distillation separation, adding excessive lanthanum nitrate solution precipitation fluoride , With chloroacetic acid as accelerating precipitating agent.Adding excess EDTA, using xylenol orange as indicator, back titrating excess EDTA with standard zinc solution, the method has the advantages of obvious, rapid and accurate determination of the fluoride content range (4 ~ 100 mg Fluorine), superior to the common thorium nitrate titration and zirconium titration methods.