Determination of total rare earths in intermediate alloy of rare earth aluminum by EDTA titration
LONG Xu-dong1,2, GAO Li-hong1,2, ZHANG Hong1,2, LIU Xiao-jie1,2
1. Rui Ke National Engineering Research Centre of Rare Earth Metallurgy and Function Materials Co., Ltd., Baotou 014030, China; 2. Baotou Research Institute of Rare Earths, Baotou 014030, China
Abstract：The accurate determination of total rare earths in intermediate alloy of rare earth aluminum is of great significance to effectively control the production technology and product quality.The sample was dissolved with 400g/L sodium hydroxide solution. At this time, rare earths reacted with sodium hydroxide to form rare earth hydroxide precipitates, while aluminum was remained in sample solution in the form of metaaluminates. The separation of aluminum from rare earths could be reached by filtration. The precipitate was dissolved with hydrochloric acid. Then hydrofluoric acid was added to react with rare earths to form rare earth fluoride precipitates, while iron would be remained in solution in the form of complex. The separation of interference element (i.e., iron) from rare earths could be reached by filtration. The precipitate was dissolved with hydrochloric acid and perchloric acid. The residual iron (III) was reduced with ascorbic acid. Little residual interference element aluminum was mashed with diacetone. The pH of solution was controlled at 5.5. The xylenol orange was used as indictor. The solution was titrated with EDTA standard solution until the color was changed from red purple to bright yellow. Thus the determination method of total rare earths in intermediate alloy of rare earth aluminum by EDTA titration was established. The proposed method was applied for the determination of total rare earths in intermediate alloy samples of rare earth aluminum (including lanthanum-aluminum, samarium-aluminum, erbium-aluminum and yttrium-aluminum). Moreover, different amounts of high-purity lanthanum oxide, samarium oxide, erbium oxide and yttrium oxide, which had been heated in muffle furnace at 950℃, was added into sample for recovery tests, respectively. The relative standard deviation (RSD, n=11) of determination results were less than 0.30%. The recoveries were between 99.6% and 100.4%. The contents of total rare earths in lanthanum-aluminum and samarium-aluminum samples were determined according to the experimental method, and the found results were basically consistent with those obtained by the oxalate gravimetric method in national standard GB/T 31966-2015.
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