Deblonde Gauthier J-P, Chagnes Alexandre, Cote Gérard, Vial Jérôme, Rivals Isabelle, Delaunay Nathalie
Chimie ParisTech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris (IRCP), F-75005 Paris, France; Eramet Research, Hydrometallurgy Department, Trappes, France.
Chimie ParisTech, PSL Research University, CNRS, Institut de Recherche de Chimie Paris (IRCP), F-75005 Paris, France.
J Chromatogr A. 2016 Mar 11;1437:210-218. doi: 10.1016/j.chroma.2016.01.075. Epub 2016 Feb 2.
Tantalum (Ta) and niobium (Nb) are two strategic metals essential to several key sectors, like the aerospace, gas and oil, nuclear and electronic industries, but their separation is really difficult due to their almost identical chemical properties. Whereas they are currently produced by hydrometallurgical processes using fluoride-based solutions, efforts are being made to develop cleaner processes by replacing the fluoride media by alkaline ones. However, methods to analyze Nb and Ta simultaneously in alkaline samples are lacking. In this work, we developed a capillary zone electrophoresis (CE) method able to separate and quantify Nb and Ta directly in alkaline media. This method takes advantage of the hexaniobate and hexatantalate ions which are naturally formed at pH>9 and absorb in the UV domain. First, the detection conditions, the background electrolyte (BGE) pH, the nature of the BGE co-ion and the internal standard (IS) were optimized by a systematic approach. As the BGE counter-ion nature modified the speciation of both ions, sodium- and lithium-based BGE were tested. For each alkaline cation, the BGE ionic strength and separation temperature were optimized using experimental designs. Since changes in the migration order of IS, Nb and Ta were observed within the experimental domain, the resolution was not a monotonic function of ionic strength and separation temperature. This forced us to develop an original data treatment for the prediction of the optimum separation conditions. Depending on the consideration of either peak widths or peak symmetries, with or without additional robustness constraints, four optima were predicted for each tested alkaline cation. The eight predicted optima were tested experimentally and the best experimental optimum was selected considering analysis time, resolution and robustness. The best separation was obtained at 31.0°C and in a BGE containing 10mM LiOH and 35mM LiCH3COO.The separation voltage was finally optimized, resulting in the separation of Nb, Ta, and IS in less than 2.5min, which is three times faster than any CE method ever reported for the separation of Nb and Ta (acidic media included). Some figures of merit of the method were determined such as linearity ranges and limits of quantitation. Finally, the method was successfully applied to the analysis of a real industrial sample.
钽（Ta）和铌（Nb）是对航空航天、天然气和石油、核能及电子工业等几个关键领域至关重要的两种战略金属，但由于它们几乎相同的化学性质，其分离非常困难。目前它们是通过使用氟化物基溶液的湿法冶金工艺生产的，人们正在努力开发更清洁的工艺，用碱性介质替代氟化物介质。然而，缺乏在碱性样品中同时分析Nb和Ta的方法。在这项工作中，我们开发了一种毛细管区带电泳（CE）方法，能够在碱性介质中直接分离和定量Nb和Ta。该方法利用了在pH>9时自然形成并在紫外区域有吸收的六铌酸盐和六钽酸盐离子。首先，通过系统方法优化了检测条件、背景电解质（BGE）的pH值、BGE共离子的性质和内标（IS）。由于BGE抗衡离子的性质改变了两种离子的形态，因此测试了基于钠和锂的BGE。对于每种碱性阳离子，使用实验设计优化了BGE的离子强度和分离温度。由于在实验范围内观察到IS、Nb和Ta迁移顺序的变化，分辨率不是离子强度和分离温度的单调函数。这迫使我们开发一种用于预测最佳分离条件的原始数据处理方法。根据对峰宽或峰对称性的考虑，有或没有额外的稳健性约束，为每个测试的碱性阳离子预测了四个最佳值。对预测的八个最佳值进行了实验测试，并考虑分析时间、分辨率和稳健性选择了最佳实验最佳值。在31.0°C和含有10mM LiOH和35mM LiCH3COO的BGE中获得了最佳分离效果。最终优化了分离电压，实现了Nb、Ta和IS在不到2.5分钟内的分离，这比以往报道的任何用于分离Nb和Ta的CE方法（包括酸性介质）快三倍。确定了该方法的一些性能指标，如线性范围和定量限。最后，该方法成功应用于实际工业样品的分析。
