Separation And Enrichment Of Sr Isotope In High Rb/Sr Samples

Strontium isotope has played an important role in the study of Sedimentology,Sequence stratigraphy,Environmental geology,Mineralogy,Hydrogeology and other fields.In the determination of Sr isotopic compositions in geological samples using MC-ICP-MS and TIMS,due to the complex composition of the sample matrix,the matrix effect is easily caused during the measurement of the instrument,which seriously interferes with the determination of Sr isotope.⁸⁷Rb and ⁸⁷Sr are isobaric elements.In mass spectrometry,⁸⁷Rb interferes with the determination of ⁸⁷Sr.Therefore,it is necessary not only to separate the matrix elements in the sample,but also to separate Rb and Sr from the sample.In general,the cation exchange resin method is used for the separation of Rb and Sr,which consumes a large amount of reagents and takes a long time,and its efficiency is low.For high Rb/Sr samples,usually one chromatographic separation does not completely separate Rb and Sr,but also requires secondary separations,even more separations,and requires a large amount of eluent and more time,so the pre-sample chemical treatment severely restricts the accurate and rapid determination of Sr isotope in samples.Shortening the separation and analysis process of Sr isotope and improving the accuracy of Sr isotope analysis are becoming the focus of research on helium isotopes.This paper proposes a new method for separation and enrichment of Sr isotope in samples,especially for high Rb/Sr samples.For high Rb/Sr samples,Fe?OH?₃co-precipitation separation was performed on the pretreated samples to remove most of the Rb and some of the matrix elements.The Sr isotope was further enriched using a self-made fully automatic solid-state isotope exchange separation device.This experimental method can save a lot of time and reduce reagent consumption.The research content of this paper's experimental method is mainly divided into the following three parts.Firstly,according to the amount of Rb and Sr in the high Rb/Sr samples,the optimal Rb and Sr addition amounts in the high Rb/Sr solution were found and a solution with Rb/Sr of 10 was prepared.The separation of Rb and Sr from the solution of high Rb/Sr was studied by co-precipitation of Fe?OH?₃.The optimum pH conditions and the addition amount of Fe were discussed in the co-precipitation separation process.The experimental results show that the separation of Rb and Sr by Fe?OH?₃ co-precipitation achieves the best effect when the pH is 10 and the co-precipitated Fe is more than 3.0 mg.The adsorption rate of Fe?OH?₃co-precipitation for Sr can reach about 99%,while the removal rate of Rb can reach97%to 99%.Secondly,this dissertation introduces the components and working principle of a self-made fully automatic solid-state isotope ion exchange separation device,and discusses the performance of this device.The results show that the device has high injection accuracy,reliable performance of flow path system,certain feasibility and good performance advantages.In order to investigate the effect of Fe?OH?₃ co-precipitation separation on the separation of Ca and Mg ions,a co-precipitation separation was performed using national geological standard rock sample GBW07106,and a solution with a Rb/Sr of10 was added after pretreatment of the rock sample.Simulate a sample solution with Rb/Sr of 10.The results showed that Mg and Ca did not remain in the supernatant but entered Fe?OH?₃ precipitates,probably due to the fact that Mg,Ca,and Sr were in the same main group.They will also be co-precipitated by Fe?OH?3.The co-precipitated sediments of the rock sample were treated and separated by a fully automatic solid-state ion exchange separation device.The separation matrix elements and Rb and Sr properties of the device were discussed.At the same time,the curves of elution of Rb and Sr from different eluents were discussed,and the optimal hydrochloric acid elution concentration of Rb and Sr was determined to be 2.5 mol/L.According to the method proposed in this paper,the recovery rate of Sr in the enriched rock samples was 91.9%.At the same time,the precision of the method was discussed.The RSD was 1.2%.The process blank of the method was between 0.009ng and 0.06 ng.Finally,this thesis mainly focuses on high Rb/Sr samples,using an international basalt standard BCR-2,and adding high purity Rb/Sr samples to verify the reliability of the method by adding purified Rb.And the international standard sample NBS 987was used to monitor the stability of the mass spectrometer.The results showed that its⁸⁷Sr/⁸⁶Sr value was 0.710256±0.000017?2??,which was basically consistent with the standard value within the error range.The measured value of the international standard BCR-2 is 0.705011±0.000008?2?,n=50?,and the theoretical recommended value is 0.70500 to 0.70510,which is also consistent within the error range of its recommended value.The results showed that the separation and purification of Sr isotope in high Rb/Sr samples was feasible and the analytical results were reliable.