Respective determination of aluminum and potassium in potassium cryolite by sodium pyrosulfate melting potentiometric titration and potassium tetraphenylborate gravimetry
WANG Xiuli, SONG Dandan, SHANG Yujun, ZHANG Jinyu
High and New Technology Research Center of Henan Academy of Sciences,Zhengzhou 450002,China
Abstract：It is necessary to accurately determine the molar ratio of K/Al in potassium cryolite in order to ensure the product quality of potassium cryolite brazing flux and its weldments.X-ray fluorescence spectrometry(XRF) has some problems such as the complicated preparation of standard sample and the difficulty of matrix correction,and cannot meet the requirements of accurate quantification.The chemical wet analysis method usually needs fractional melting of samples,and the determination process is cumbersome.In this study,the sample was melted and decomposed at 700 ℃ for 30 min using 6 g of sodium pyrosulfate.The excessive EDTA-fluoride replacement method was employed.The replaced EDTA was determined by potential titration using ZnCl2 standard titration solution at DET mode with the wavelength of 574 nm.The interference of metallic impurity ions such as iron and titanium with the determination of aluminum in potassium cryolite was solved effectively.The method for the determination of aluminum in potassium cryolite by potentiometric titration was established.Under alkaline conditions,10 mL of precipitant was added at the rate of 6 to 8 seconds per drop at beginning and then 2 to 3 seconds per drop.The ions such as aluminum,iron,calcium and magnesium were masked with EDTA.The method for the determination of potassium in potassium cryolite by potassium tetraphenylborate gravimetry was established.The pretreatment method of once sample melting with sodium pyrosulfate avoided the tedious steps of fractional melting of sample.The contents of aluminum and potassium in actual sample of potassium cryolite were determined according to the experimental method,and the relative standard deviations (RSD,n=6) of determination results were less than 0.2%.The determination results were compared with those obtained by other methods(the content of aluminum was determined by EDTA titration in YS/T 273.4-2020,and the content of potassium was determined by alkaline sodium hydroxide melting-potassium tetraphenylborate gravimetry),and the absolute errors were less than 0.4%.
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