铅试金-电感耦合等离子体质谱法测定斑岩铜矿中金铂钯

斑岩铜矿中Au、Pt、Pd的准确测定,对于提高斑岩铜矿的综合利用水平具有十分重要的意义。斑岩铜矿中伴生贵金属含量低、基体复杂、测定难度大。实验以铅作试金捕集剂,提出一种用瓷碟熔炼、两步灰吹的分离富集方法,选择¹⁹⁷Au、¹⁹⁵Pt、¹⁰⁶Pd为测定同位素,以¹¹⁵In对¹⁰⁶Pd、¹⁸⁵Re对¹⁹⁷Au和¹⁹⁵Pt进行校正,建立了铅试金富集-电感耦合等离子体质谱法(ICP-MS)测定斑岩铜矿中Au、Pt、Pd的分析方法。通过对试金配料组成进行考察,确定试金配料由质量比为5∶2∶2∶1的氧化铅、硼酸、碳酸钠和面粉组成。对样品量、配料质量、瓷碟容积、熔融温度进行了优化,最终确定样品量为5 g,配料质量为50 g,瓷碟容积为40 mL,熔融温度为1 000 ℃。灰吹试验表明,打开炉门先直接在瓷碟中灰吹(950 ℃)除去部分铅,待铅扣被熔渣覆盖后,取出铅扣并转移到镁砂灰皿中进一步灰吹(920 ℃)除去剩余的铅,可获得满意的银合粒。灰吹干扰试验表明,虽然一些易被还原或者易溶解于铅中的元素如Cu、Ni、Bi、As、Sb、S、Se、Te等也会进入铅扣中,但其对灰吹过程的干扰可忽略。质谱干扰试验表明,试液中残留量的Cu、Ni、Se和Ag所产生的质谱干扰可忽略。方法中各元素校准曲线的相关系数均在0.999以上,方法检出限分别为Au 0.10 ng/g、Pt 0.05 ng/g、Pd 0.08 ng/g,定量限分别为Au 0.33 ng/g、Pt 0.17 ng/g、Pd 0.27 ng/g。按照实验方法测定斑岩铜矿样品中的Au、Pt、Pd,结果的相对标准偏差(RSD,n=7)为2.7%～9.5%,加标回收率在96%～107%之间。采用国家标准GB/T 20899.1—2019中火试金-火焰原子吸收光谱法测定Au,地质矿产行业标准DZ/T 0279.31—2016中火试金富集-电感耦合等离子体质谱法测定Pt和Pd进行方法对照,实验方法测定值与标准方法基本吻合。

Determination of gold,platinum and palladium in porphyry copper ore by inductively coupled plasma mass spectrometry with lead fire assay

The accurate determination of Au, Pt and Pd in porphyry copper ore is of great significance to improve its comprehensive utilization level. However, the contents of associated precious metals in porphyry copper ore are low, and the matrix is complex, leading to high difficulty in determination. A new separation and preconcentration method including porcelain disc melting and two-step cupellation was proposed with lead as the trapping agent. ¹⁹⁷Au,¹⁹⁵Pt and ¹⁰⁶Pd were selected as the isotopes for determination. ¹¹⁵In was used as internal standard for the correction of ¹⁰⁶Pd, and ¹⁸⁵Re was used as internal standard for the correction of ¹⁹⁷Au and ¹⁹⁵Pt. Consequently, a method for determination of Au, Pt and Pd in porphyry copper ore by inductively coupled plasma mass spectrometry (ICP-MS) with lead fire assay preconcentration was established. Through the tests of assay ingredient composition, the assay ingredient was determined to be composed of lead oxide, boric acid, sodium carbonate and flour with the mass ratio of 5∶2∶2∶1. The sample mass, ingredient mass, porcelain disc volume and melting temperature were optimized as follows: the sample mass was 5 g, the ingredients mass was 50 g, the porcelain disc volume was 40 mL, and the melting temperature was 1 000 ℃. The cupellation test showed that the first cupellation (950 ℃) was directly conducted in porcelain disc by opening the furnace door to remove partial lead. After the lead button was covered with the slag, the lead button was taken out and transferred to magnesia cupel for further cupellation (920 ℃) to remove the residual partial lead. Thus, the satisfactory silver granule was obtained. The cupellation interference test showed that, although some elements, which were easily reduced or dissolved in lead, such as Cu, Ni, Bi, As, Sb, S, Se and Te, would also enter lead button, their interference with the cupellation process could be ignored. The mass spectrometry interference test showed that the interference of residual Cu, Ni, Se and Ag in test solution could be also ignored. The correlation coefficients of calibration curves for all elements were higher than 0.999. The limit of detection for Au, Pt and Pd was 0.10 ng/g, 0.05 ng/g, and 0.08 ng/g, respectively. The limits of quantification for Au, Pt and Pd was 0.33 ng/g, 0.17 ng/g, and 0.27 ng/g, respectively. The contents of Au, Pt and Pd in porphyry copper ore samples were determined according to the experimental method. The relative standard deviations (RSD, n=7) of determination results were between 2.7% and 9.5%. The spiked recoveries were between 96% and 107%. The results were basically consistent with those obtained by the national standard of GB/T 20899.1-2019 for determination of Au by flame atomic absorption spectrometry with fire assay, and the industrial standard of DZ/T 0279.31-2016 for determination of Pt and Pd by inductively coupled plasma mass spectrometry with fire assay.