Chemical Pre-treatment Methods for Measurement of Ge Isotopic Ratio on Sphalerite in Lead-Zinc Deposits
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摘要:
目前Ge同位素研究主要局限于地球有机质(煤等)、火成岩及陨石样品,作为Ge重要储库之一的铅锌矿床,其Ge同位素的研究涉及较少。铅锌矿床样品中Ge的化学分离及提纯是Ge同位素研究的基础。本文详细考察了陨石样品中Ge同位素预处理方法(分离和提纯)对铅锌矿石样品的适用性。阴离子条件实验说明,目前普遍采用的离子交换树脂单柱法虽然对铅锌矿样品中Fe、Se等元素的剔除效果理想,但无法有效剔除其中的Zn,当Zn/Ge比值大于3时,样品必须经过阳离子交换树脂柱作进一步处理剔除Zn。通过对闪锌矿标准样品、锌矿石标准样品的条件实验以及实际闪锌矿样品对条件结果的验证显示,当闪锌矿的称样量为0.15 g左右时,仅需将前人对玄武岩等样品Ge同位素处理方法中阴离子树脂洗脱酸(1.4 mol/L硝酸)的用量6 mL调整为10 mL,而阳离子树脂洗脱方法保持不变,此方法即满足闪锌矿样品Ge同位素的化学分离和提纯要求。样品经过本文推荐的阴阳离子交换树脂双柱法处理后,主要干扰元素(Fe、Zn、Se、Ni)及基质元素的剔除率接近100%,Ge的回收率优于99%。而前人对玄武岩等样品的Ge同位素处理方法中,主要干扰元素(Fe、Zn、Se、Ni)及基质元素的剔除效果亦较好,但Ge的回收率仅为97.3%,比本文推荐方法的Ge回收率要差。利用MC-ICP-MS对Ge化学分离和提纯后的富乐铅锌矿床闪锌矿样品的检验结果显示,测试过程中未见同质异位素以及可能的多原子离子影响,样品中Ge同位素符合质量分馏定律,经过调整后的阴阳离子交换树脂双柱法满足闪锌矿样品的Ge同位素测试要求。
Abstract:Up to the present, main research of Ge isotopes has been carried out on organic, magmatic and meteoritic samples. Pb-Zn deposits are one of the most important reservoirs of Ge; however, there are few studies on Ge isotopes for these samples. Ge separation and purification for samples collected from Pb-Zn deposits are the basis of Ge isotope research. Therefore, the suitability for Pb-Zn ores of the Ge isotopic purification method established for meteoritic samples in details has been investigated. The results demonstrate that anion exchange resins single-column method for Pb-Zn ores can eliminate the potential interferences efficiently (including Fe, Se and other interfering matrix elements), but does not work for Zn as Zn/Ge>3, indicating that further separation and purification by ion-exchange column are needed to eliminate Zn. Conditional experiments of standard samples (ores and sphalerite) and three sphalerite samples from the Fule deposits showed that adjusting the volume of anion exchange resin elution acid (1.4 mol/L, HNO3) from 6 mL to 10 mL and maintaining the method of cation exchange resin is suitable for Ge isotope purification. The results of anion/cation exchange resin two-column procedure indicate that the recovery of Ge was better than 99%, and the potential interferences on Ge isotopes (including Fe, Se, Zn and other interfering matrix elements) were almost 100% eliminated. Although the previous method has a good recovery of Ge (97.3%) and the potential interferences on Ge isotopes (including Fe, Se, Zn and other interfering matrix elements) were reduced to the negligible levels, the recovery is lower than the recommended method in this paper. Furthermore, the Ge isotopic composition of three sphalerite samples from the Fule deposit show that there are no signals coming from interfering elements and matrix elements, and the mass fractionation of Ge isotope followed the rule of mass-dependent fractionation. Overall, this modified method for Ge isotope measurement is suitable for sphalerite samples.
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Key words:
- Ge isotopes /
- sphalerite /
- separation and purification /
- pre-treatment method
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表 1 Ge同位素质谱分析过程中可能的同质异位素、多原子离子的干扰
Table 1. Major potential interferences for Ge isotopes
质量数 Ge
(%)Se
(%)Zn
(%)可能的分子离子干扰 70 20.55 0.62 54Fe16O等 72 27.37 56Fe16O等 73 7.67 56Fe16O1H等 74 36.74 0.87 57Fe16O1H,58Ni16O等 76 7.67 9.02 60Ni16O等 表 2 参照文献[6]设计的阴离子树脂条件实验
Table 2. The designed condition experiment of anion exchange resin according to literature [6]
流程及各物质用量
(mL)文献[6]的用量
(mL)1#样品
(锌矿石)2#样品
(锌矿石)3#样品
(锌矿石)4#样品
(锌矿石)5#样品
(闪锌矿)6#样品
(闪锌矿)备注 阴离子树脂 1.8 1.8 1.8 1.8 1.8 1.8 1.8 - 1.4 mol/L硝酸 10 10 10 10 10 10 10 洗涤 超纯水 4 4 4 4 4 4 4 洗涤 1 mol/L氢氟酸 10 10 10 10 10 10 10 平衡 引入样品量 2 2 2 2 2 2 2 - 1 mol/L氢氟酸 5 5 10 5 10 5 5 洗涤 超纯水 2 2 2 2 2 2 2 洗涤 1.4 mol/L硝酸 6 6 10 10 6 10 6 收集 表 3 参照文献[6]设计的阳离子树脂条件实验
Table 3. The designed condition experiment of cation exchange resin according to literature [6]
试验流程 文献[6] 7#样品 8#样品 9#样品 10#样品 11#样品 阳离子树脂(mL) - 2 2 2 2 2 0.14 mol/L硝酸(mL) - 10 10 10 10 10 引入样品量(mL) 1.5 2 2 3 3 2 0.14 mol/L硝酸(mL) 3 2 3 4 3 4 注:7#~11#样品为5#~6#样品(闪锌矿)经阴离子树脂处理后的混合液所配制的平行样品。 表 4 阴离子树脂条件实验测试结果
Table 4. Analytical results for anion exchange resin condition experimen
流程及各物质
的用量1#样品
(锌矿石)2#样品
(锌矿石)3#样品
(锌矿石)4#样品
(锌矿石)5#样品
(闪锌矿)6#样品
(闪锌矿)检测元素 Fe Se Zn Fe Se Zn Fe Se Zn Fe Se Zn Se Zn Se Zn 引入样品总含量(μg/g) 699 103 945 699 103 945 699 103 945 699 103 945 0.4 75237 0.4 75237 1 mol/L氢氟酸(mL) 704 99 894 705 99 890 708 99 897 738 96 921 - - - - 超纯水(mL) / 1.0 3.4 / 1.0 1.1 / 1.1 4.2 / / 1.0 - - - - 1.4 mol/L硝酸(mL) / 0.7 # / 1.5 0.9 / 1.3 3.2 / / # * 22.4 * 18.5 引入样品Ge总含量(μg/g) 513.8 513.8 513.8 513.8 6.05 6.05 过阴离子后Ge总含量(μg/g) 500.0 524.0 531.0 504.0 6.25 5.95 Ge回收率(%) 97.3 101.9 103.3 98.1 103.2 98.3 注:“-”表示未测试,“/”表示低于ICP-AES检测限, “#”表示低于ICP-MS检测限,“*”表示低于AFS-810型原子荧光光谱仪的检测限。所有经过阴离子树脂纯化的样品的Ge含量利用ICP-MS测定。样品4中过完阴离子树脂的Fe含量比进样的Fe含量更高,可能是由于测量误差或者受到污染导致的。 表 5 阳离子树脂条件实验结果
Table 5. Analytical results for cation exchange resin condition experiment
干扰元素剔除效果评价 7#样品 8#样品 9#样品 10#样品 11#样品 化学分离前Zn总量(μg/g) 7.16 7.16 10.74 10.74 7.16 化学分离后Zn总量(μg/g) 0.03 0.02 0.04 0.03 0.11 化学分离前Ge总量(μg/g) 1.50 1.50 2.25 2.25 1.50 化学分离后Ge总量(μg/g) 1.44 1.46 2.10 2.01 1.50 过完阳离子树脂后Zn/Ge比值 0.02 0.02 0.02 0.01 0.07 Ge回收率(%) 96.1 97.7 93.3 89.3 100.2 表 6 闪锌矿标准样品(GBW 07270) 经阴阳离子处理后各元素平均值及阳离子条件实验结果
Table 6. Analytical results for sphalerite standard (GBW 07270) after chemical purification and separation of Ge isotope
实验过程及结果 Co Ni Cu Zn Ga Ge As Se Zr Cd In Sb W Pb 储备液含量(μg/g) 59.1 5.2 120.4 75237 30.2 53.4 3.3 0.4 - 180.5 2.5 29.9 - 119 阴离子处理后含量(ng/g) 18.6 3.3 62.8 21518.0 0.4 1499.8 69.6 * 41.5 336.4 25.2 6380.0 88.7 684.4 阳离子条件液含量(ng/g) 5.5 1.1 24.9 7161.5 2.1 1499.8 17.9 * 7.5 60.8 3.5 1400.8 17.9 311.9 7#样品各元素含量 0.0 0.5 17.9 37.8 0.0 1442.0 15.5 * 1.0 / / 545.8 0.0 13.4 8#样品各元素含量 0.1 0.8 11.0 25.3 0.1 1466.5 16.1 * 0.5 / / 1081.6 2.1 12.7 9#样品各元素含量 0.0 1.0 15.2 48.7 0.2 2099.0 23.8 * 0.9 / 0.1 1810.0 1.8 22.9 10#样品各元素含量 0.0 1.5 14.7 38.3 0.1 2129.0 26.6 * 1.2 / 0.1 1553.9 1.1 24.1 11#样品各元素含量 0.2 1.4 12.2 112.2 0.1 1503.6 17.4 * 0.5 / 0.0 1256.5 5.3 18.3 注:储备液的元素含量是根据闪锌矿的标准样品推荐值换算,“-”表示没有推荐值,过阴离子的样品元素含量为ICP-MS测试结果。“/”表示低于ICP-MS的检测限。“*”表示低于AFS-810型原子荧光光谱仪的检测限。 表 8 实际闪锌矿样品分析结果
Table 8. Analytical results for sphalerite samples
样品编号 含量(μg/g) Li Be Sc V Cr Co Ni Cu Zn Ga Ge As 1 0.222 - - - 0.011 0.003 0.009 0.319 2.148 - 103.218 10.118 2 0.200 - - - - - - 0.345 2.547 - 86.742 2.692 3 0.202 - - - 0.099 0.003 - 0.408 2.583 - 99.506 4.873 样品编号 Rb Sr Y Zr Nb Mo Ag Cd In Sn Sb Cs 1 0.044 - - 0.083 - 0.012 - 0.002 - - 57.548 0.000 2 0.035 - - - - - 0.001 - - - 154.951 0.000 3 0.040 - - 0.001 0.010 -0.009 0.004 - - - 107.227 - 样品编号 Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er 1 - 0.004 0.001 0.000 - - - - 0.000 0.001 0.000 - 2 - 0.005 0.003 0.000 - - - - 0.000 - 0.000 - 3 - 0.002 - - - - - - 0.000 - 0.000 0.000 样品编号 Tm Yb Lu Hf Ta W Tl Pb Bi Th U 1 0.000 - 0.001 - 0.000 1.928 - 1.462 - - 0.002 2 0.000 - 0.000 - 0.000 1.565 - 1.693 - 0.000 0.004 3 0.000 - - - 0.000 3.621 - 1.987 - - 0.003 注:“-”表示低于ICP-MS的检测限。 表 9 闪锌矿的Ge同位素组成
Table 9. Ge isotopic compositions of sphalerite samples
样品编号 δ74Ge/70Ge 2SD δ72Ge/70Ge 2SD δ73Ge/70Ge 2SD 样品1 -2.61 0.35 -1.26 0.21 -2.00 0.27 样品2 -4.12 0.06 -2.03 0.02 -3.13 0.10 样品3 -1.91 0.44 -0.95 0.21 -1.49 0.32 JMC标准 0.04 0.23 0.03 0.16 0.02 0.23 -
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