EDTA滴定法测定稀土铝中间合金中稀土总量

准确测定稀土铝中间合金中稀土总量,对于有效控制稀土铝中间合金的生产技术和产品质量具有重要意义。用400g/L氢氧化钠溶液溶解试样,此时,稀土与氢氧化钠反应生成氢氧化稀土沉淀,而铝与氢氧化钠反应后以偏铝酸根的形式留在了试液中,过滤,实现了铝与稀土元素的分离;用盐酸溶解沉淀,加入氢氟酸,此时稀土和氢氟酸反应生成氟化稀土沉淀,而铁与氢氟酸反应形成络合物留在溶液中,过滤,实现了干扰元素铁与稀土元素的分离;加入盐酸和高氯酸溶解沉淀,用抗坏血酸还原残留铁(Ⅲ),乙酰丙酮溶液掩蔽残留的少量干扰元素铝,控制pH 5.5,以二甲酚橙作指示剂,用EDTA标准溶液滴定至溶液由红紫色变为亮黄色即为终点,建立了EDTA滴定法测定稀土铝中间合金中稀土总量的方法。将实验方法用于稀土铝中间合金(镧铝、钐铝、铒铝、钇铝)试样中稀土总量的测定,并在试样中分别加入不同量的于950℃马弗炉中灼烧过的高纯氧化镧、高纯氧化钐、高纯氧化铒和高纯氧化钇试剂进行加标回收试验,结果的相对标准偏差(RSD,n=11)不大于0.30%,加标回收率为99.6%～100.4%。选取镧铝、钐铝试样,按照实验方法测定其中稀土总量,并采用国标GB/T...

Determination of total rare earths in intermediate alloy of rare earth aluminum by EDTA titration

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.