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锍镍试金技术制备含铂族元素硫化物微区分析标准样品的可行性

Feasibility Study of Synthesizing PGE-Bearing Sulfide Reference Material by Remelted Nickel Sulfide Fire Assay Button

  • 摘要: 激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)适合于直接分析硫化物矿物中痕量元素的含量及空间分布,但硫化物矿物的激光剥蚀特性与硅酸盐及氧化物不同,受到的干扰也更严重,且由于硫化物标准物质(尤其是含铂族元素、Au、Ag等贵金属元素标准物质)极度缺乏,限制了LA-ICP-MS技术在硫化物微区分析中的广泛应用。本文以贵金属标准样品GPT-9和矿石标准物质为原料合成锍镍试金扣,并封入真空管中重熔,利用背散射电子图像和LA-ICP-MS分析元素分布的均匀性,探讨真空重熔锍镍试金扣制备硫化物原位微区分析标准样品的可行性。背散射电子图像(BSE)显示真空重熔后锍镍试金扣由单相S、Ni化合物组成。LA-ICP-MS线扫描和点扫描分析表明,锍镍试金扣中S、Ni、Cr、Co、Cu、Pb、Sb、Cd、Bi等主量及微量元素分析精密度(RSD)均小于10%,均匀分布;在镍扣制备过程中Zn相对于Cu、Pb、Sb更难进入硫化物相;贵金属元素Au、Ag、Pt均一性较好,其余贵金属元素由于含量低、仪器波动及质谱干扰等影响因素造成分析数据的RSD相对较大,但可通过提高原料中贵金属元素含量、降低熔融样品淬火温度等方法进一步提高其均匀性。锍镍试金扣的组成元素对铂族元素分析的质谱干扰研究表明,重铂族元素(Os、Ir、Pt)和Au受到的干扰可忽略不计;轻铂族元素(Ru、Rh、Pd)受金属氩化物干扰较为严重,需进行干扰校正。研究认为,真空重熔技术可有效提高锍镍试金扣中各元素(包括贵金属)的均一性,达到硫化物原位微区分析标准样品的要求,利用真空重熔锍镍试金扣制备LA-ICP-MS原位微区痕量及贵金属硫化物分析标准样品具可行性。

     

    Abstract: Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) is suited to analyze the abundances and spatial distributions of trace elements in sulfide. However, the spread use of the technology on micro area analysis has been hampered by the different characteristics of sulfides from silicates and oxides and the lack of sulfide reference material, especially PGE-bearing reference material. In this study, a PGE-bearing sulfide (SRMD-1) is synthesized by remelted nickel sulfide fire assay button in AN evacuated quartz tube. The examination by BSE imaging revealed that the nickel button SRMD-1 was completely of monosulfide composition. Homogeneity testing by LA-ICP-MS shows that the RSDs of elements, such as S, Ni, Cr, Co, Cu, Pb, Sb, Cd, Bi, are less than 10%. The data suggest the homogeneous distribution of these elements inside SRMD-1, but elements Mn, Zn, Sn, Tl are not as homogeneous with relatively larger RSDs. Elements Ag, Au and Pt are homogeneous inside SRMD-1, but RSDs of other noble metal elements are relatively larger according to low element content, instrument fluctuations or mass spectrometry interference. The homogeneity of the nickel button will be improved by increasing the content for the noble metal elements and lowering the quenching temperature for the molten samples. During the analysis of the nickel sulfide fire assay button, the spectral interferences in light PGEs (Ru, Rh and Pd) by argides is serious, and must be corrected, while the interferences to Os, Ir, Pt and Au can be ignored. Compared to the button which is not remelted, the homogeneity of the elements improved significantly. According to the work documented here, it is possible to synthesized PGE-bearing sulfide reference material for LA-ICP-MS by remelted nickel sulfide fire assay button.

     

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