特殊地质样品中钼同位素分析的化学前处理方法研究. (Chinese)

Research on the Chemical Pretreatment of Special Geological Samples' Mo Isotopes Analysis. (English)

BACKGROUND: The research of Mo isotopes applys to the earth science widely, and the Mo isotope composition can offer information about global Mo isotopes circulation, redox conditions of paleo-ocean, mineralizing process, cosmic sites' evolution, et al. Before the analysis of Mo isotopes by multi-collector inductivity coupled plasma-mass spectrometry (MC-ICP-MS), the samples must be pretreated to ensure the accuracy of mass spectrometry. The pretreatment consists of purificating the determined element (Mo) and separating the interfering element (Zr, Ru, Fe, Mn, et al.). When dealing with the Ca-bearing geological samples with high Fe content such as pyrite-bearing calcareous mudstone and calcareous shale, if researchers adopt the previous method of anion-cation exchange resin with double column, the cation resin will be used repeatedly to separated Fe, lead more workload and lower Mo recovery; if researchers adopt the previous of anion exchange resin with single column, the eluent of 1mol/L HF-0.1mol/L HCl will combine the samples' Ca to generate insoluble percipitate. OBJECTIVES: To exploration a new method apply for the Ca-bearing geological samples with high Fe content, according to the previous pretreatment methods. METHODS: This research uses the anion resin(AG1-X8 resin, 100-200 mesh) with single-column, and the samples will be washed by two steps with different eluent (first step's eluent is 6mol/L HCl, and second is 1mol/L HF+0.1mol/L HCl and 6mol/L HCl). RESULTS: The data of artificial samples with high Ca and Fe content shows this method's Mo recovery rate >96%, and the removal of the interfering elements reach the ideal target, especially the removal rate of Ru is higher than the previous methods by~12%, up to 100%. The outcome of chemical pretreatment and mass spectrometry for the geological samples also indicates the Mo recovery rate and the interfering elements' removal rates meet the requirement of the analysis of Mo isotopes by MC-ICP-MS, and the acquired δ^98/95Mo values are consistent with those in the literature. CONCLUSIONS: The modified separation method of anion exchange resin with single column-double elution can apply to the special geological samples with high Ca and Fe content, have lower cost than the previous methods, and this method would apply to the most geological sample. [ABSTRACT FROM AUTHOR]

Mo同位素的研究在地学领域应用广泛，它可以示踪Mo的全球循环、古海洋氧化还原条件、成矿过程、天体演化过程等。多接收器电感耦合等离子体质谱仪（MC-ICP-MS）分析Mo同位素比值前需对样品进行分离纯化，以富集Mo和去除Zr、Ru、Fe、Mn等干扰元素。处理某些Fe含量特别高且Ca含量也高的特殊地质样品（如含大量黄铁矿的钙质泥岩、钙质页岩等），若根据传统的阴阳离子交换树脂双柱法，需多次使用阳离子交换树脂分离Fe，步骤较繁琐且Mo回收率也会降低，而根据传统的阴离子交换树脂单柱法，使用1mol/L氢氟酸+0.5mol/L盐酸介质会产生较多CaF2沉淀影响分离纯化效果。针对此类特殊地质样品，本实验使用同一阴离子树脂柱（AG1-X8 resin，100~200目）对样品进行两次淋洗，第一次使用6mol/L盐酸，第二次使用1mol/L氢氟酸+0.1mol/L盐酸和6mol/L盐酸。结果表明Mo的回收率>96%，干扰元素的去除效果好，尤其是Ru的去除率接近100%，比原方法提高了约12%。对实际样品进行实验的结果也显示，Mo的回收率和干扰元素的去除都符合要求，δ^98/95Mo测定值与文献报道值一致。改进后的阴离子交换树脂单柱-二次淋洗法适用于Fe、Ca含量较高的特殊样品，降低了分析成本，也适用于绝大多数地质样品。 [ABSTRACT FROM AUTHOR]

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