ICP-MS分析用地质样品制备过程中Nb、Ta等元素的特殊化学行为  

Specific chemical behavior of Nb and Ta in geological sample preparation with PTFE Bomb for ICP-MS analysis

作　　者：童春临[1] 刘勇胜[1] 胡圣虹[1] 胡兆初[1] 宗克清[1] 陈海红[1] 

机构地区：[1]中国地质大学地球科学学院,地质过程与矿产资源国家重点实验室,湖北武汉430074

出　　处：《地球化学》2009年第1期43-52,共10页Geochimica

基　　金：国家重点基础研究发展计划项目(2003CB716501);国家自然科学基金(40521001,40673026);教育部长江学者和创新团队发展计划(IRT0441);教育部新世纪优秀人才支持计划项目(NCET05-0664)

摘　　要：常规PTFE对瓶亚沸蒸馏HF时,Nb、Ta等部分高场强元素提纯效果较差,甚至适得其反,暗示Nb、Ta在HF蒸馏过程中存在"挥发"作用。然而,高温、高压酸溶法溶解岩石样品时,Nb、Ta等并没有表现出类似的"挥发"作用。对Nb、Ta等在高温、高压酸溶法溶样过程不同实验阶段的行为进行了详细研究。研究结果表明岩石样品中的Al、Fe、Mg、Ca等主元素基体会影响Nb、Ta等元素在溶液中的存在形式和稳定性。当基体元素与Ta含量比值达到1×104以上时,Nb、Ta在稀硝酸介质中可以稳定存在,Ta回收率达到100%。进一步的研究结果表明,在HF中加入Al、Fe等基体,可以明显降低HF蒸出液中Ta浓度,增强HF中Ta等元素的提纯效果。在用于ICP-MS分析的样品化学制备过程中Nb、Ta表现出了不同的化学行为,在以稀硝酸为介质的Nb、Ta溶液中Ta的水解聚合程度和可能性远远大于Nb。因此,除了在样品提取前使样品溶液中保留足够的HF介质外,要获得准确的Nb/Ta比值应充分延长Ta的积分时间或者采用时间分辨分析信号平均值。Hydrofluoric acid is difficult to be effectively purified with sub-boiling distillation in terms of Ta, Nb and some other high field strength elements （HFSE）, which potentially suggests that Nb and Ta could be ＂evaporated＂ accompanying HF. On the other hand, Nb and Ta could be ＂lost＂ in diluted nitric acid solution due to hydrolysis. Our routine analyses of geological samples digested with PTFE Bomb （HF ＋ HNO3） indicate that these elements were not always lost during sample preparation, which implies that stabilities of Nb and Ta were controlled by some components in addition to HF. In this work, several experiments were conducted to investigate the specific behavior of Nb and Ta during sample digestion with PTFE Bomb for ICP-MS analysis. The results indicate that major metal components （e. g., Al, Fe, Mg, and Ca） in rocks could play a comparable role in stabilizing Nb and Ta species. Ta in diluted nitric acid solution （i. e. 2% HNO3） could be stabilized by concentrated metal cation （e. g., Al/Ta 〉 10^4）, which are consistent with the generally good results of routine analyses of geological samples. Alternatively, enough amounts of HF could prevent hydrolysis of Ta in diluted nitric acid solution as well to obtain satisfactory recovery. Nb shows different chemical behavior from Ta more easily hydrolyzed/polymerized than Nb in diluted during the chemical preparation for ICP-MS analysis. Ta is nitric acid solution. On the other hand, our work suggests that hydrofluoric acid could be effectively ptrified in terms of Nb and Ta with sub -boiling distillation by mixing with additional concentrated metal matrix （e. g., Fe, Al）.

关 键 词：高压酸溶法 Ta稳定性 主元素基体 HF提纯 

分 类 号：P595[天文地球—地球化学] P599[天文地球—地质学]