碱熔-EDTA络合滴定法测定含氟铈基稀土抛光粉中氟

含氟铈基稀土抛光粉中氟含量为1%~8%(质量分数),采用水蒸气蒸馏法处理样品时操作繁琐不易掌握。实验选择氢氧化钠-过氧化钠混合熔剂高温(750℃)熔融样品10min,再用水浸取过滤,使氟全部转至滤液中并与稀土分离,调节酸度为pH2左右以过量镧沉淀氟,煮沸1~2min,在六次甲基四胺-盐酸缓冲体系下用EDTA滴定剩余镧,间接测定样品中氟含量。实验方法用于测定含氟铈基稀土抛光粉中氟,结果的相对标准偏差(RSD,n=11)为0.88%~2.9%;方法用于标准样品抛光粉GSB04-3426-2017中氟的测定,测定值与认定值一致;分别按照实验方法和国标GB/T 20166.2—2006中的方法对标准样品GSB04-3426-2017和含氟铈基稀土抛光粉实际样品中氟进行测定,两种方法测定结果相吻合。

Determination of fluorine in fluorine-containing cerium-based rare earth polishing powder by alkali fusion-EDTA titration

The content of fluorine in fluorine-containing cerium-based rare earth polishing powder is 1%-8% (mass fraction). During the sample treatment by steam distillation, the operation is cumbersome and difficult to master. The sample was melted with sodium hydroxide-sodium peroxide mixed flux at high temperature (750℃) for 10min followed by water leaching and filtration. The fluorine in sample was totally transferred to filtrate, realizing the separation with rare earths. The pH of solution was adjusted to about 2 to precipitate fluorine with excessive lanthanum. After boiling for 1-2min, the residual lanthanum was titrated with EDTA in hexamethylenetetramine-hydrochloric acid buffer system. The content of fluorine in sample was indirectly determined. The proposed method was applied for the determination of fluorine in fluorine-containing cerium-based rare earth polishing powder. The relative standard deviations (RSD, n=11) of measurement results were between 0.88% and 2.9%. The content of fluorine in standard sample of polishing powder (GSB04-3426-2017) was determined according to the experimental method, and the found results were consistent with the certified values. The contents of fluorine in standard sample (GSB04-3426-2017) and actual sample of fluorine-containing cerium-based rare earth polishing powder were determined according to the experimental method and the method in national standard GB/T 20166.2-2006. The determination results of two methods were consistent.