黄铁矿Re-Os同位素定年化学前处理若干条件初探

Preliminary study on sample-preparation for Re-Os isotopic dating of pyrite

对黄铁矿Re-Os同位素定年化学前处理过程中的溶样温度、溶样酸介质及溶样时间进行了条件实验。温度实验结果表明, 溶样温度对Re的测定结果影响不大, 而对Os的测定结果影响较明显。溶样温度在120~220 ℃之间时, 无论是HNO3还是逆王水溶样, Re含量在误差范围内都是一致的, 但在120 ℃、 150 ℃时, Os的含量偏离真实值, 可能是样品和稀释剂中的Os同位素并未完全达到平衡, 在180 ℃、200 ℃和220 ℃时, Os的含量基本一致且接近真实值。溶样酸介质实验表明, HNO3和逆王水溶样对Re的测定影响不大, 而对Os的测定影响较明显。无论是用HNO3还是逆王水溶样, 在不同温度下所得到的Re含量是一致的, 而在120 ℃、150 ℃时, 逆王水溶样较HNO3溶样所得到的Os含量更加接近真实值, 180 ℃、200 ℃和220 ℃时, 两种酸介质溶样得到的Os含量基本一致且接近真实值。用逆王水在200 ℃时溶样, 时间为5 h、8 h、12 h、18 h所得到的Re、187Os含量基本一致, 说明较高温度下在较短的时间内便能达到较好的溶样效果。Fe3＋浓度对Re的阴离子交换效率实验表明, Re的回收率随着Fe3＋浓度的不断升高而逐渐下降。当黄铁矿取样量为3 g时, 上柱体积控制在40 mL左右可获得较高的Re回收率。

Different digestion conditions, including temperature, acids and time, were tested for Re-Os isotopic dating of pyrite. The results show that the digestion temperature and different acids medium have no effect on Re results but have significant effect on Os. The results of Os are much lower than the true values, when digestion temperature at 120~150 ℃, this may probably due to isotope disequilibrium between 190Os spike and Os in samples. When temperature at 180 ℃, 200 ℃ and 220 ℃, the results are basically the same and in agreement with the true values. Re results are similar to each other within error using HNO3 or inverse aqua regia as digestion medium at different temperatures, whereas Os concentrations are much closer to the true values under inverse aqua regia digestion than HNO3 digestion at 120 ℃ and 150 ℃. Os concentrations are similar to each other within error from 180 ℃ to 220 ℃, irrespective of the digestion acids. Coincident Re, 187Os contents have been obtained by digesting with inverse aqua regia at 200 ℃ for 5 h, 8 h, 12 h and 18 h, indicating that good results can be obtained for a relatively short time of digestion. The experiments of c（Fe3＋） on anion-exchange efficiency of Re show that the recovery of Re decrease sharply with increasing c（Fe3＋）. When the sampling weight of pyrite reaches three grams, diluting the solution to 40 mL will get a good recovery of Re.