Analytical Constraints on the Measurement of the Sulfur Isotopic Composition and Concentration of Trace Sulfate in Phosphorites: Implications for Sulfur Isotope Studies of Carbonate and Phosphate Rocks
Analytical Constraints on the Measurement of the Sulfur Isotopic Composition and Concentration of Trace Sulfate in Phosphorites: Implications for Sulfur Isotope Studies of Carbonate and Phosphate Rocks
复制标题
DOI：
10.1111/j.1751-908x.2010.00102.x
复制
发表时间：
2011-06
影响因子：
3.8
通讯作者：
T. Goldberg;G. Shields;R. Newton
中科院分区：
文献类型：
--
作者：
T. Goldberg;G. Shields;R. Newton
本研究的目的是评估现有的方法提取微量硫酸盐和测量其浓度和硫同位素组成的黄铜矿。磷质岩经过化学和热处理以去除钙芒硝中的非结构性SO 42 −，否则这些非结构性SO 42 −会被无意中包含在结构结合硫酸盐的地球化学分析中。乙酸（10%v/v）被证明是有效的，在去除方解石，白云石和铁白云石，而不影响脆钙石。为了去除所有“易”溶解的硫酸盐，如硫酸钙和吸附的硫酸盐，大多数样品必须重复用10% v/v NaCl冲洗数次。对于随后的S同位素测定，发现在600 °C下燃烧样品是去除非含硫矿物相的有效方法。在测试的许多SO 42 −检测方法中，ICP-AES被证明是最准确的。对于硫酸钙回收，我们推荐的方案包括用10% NaCl和NaOCl重复冲洗粉末状磷矿石，并在每次洗涤中测试滤液中的SO 42 −。如果只需要S同位素组成，则可以在600 °C下燃烧，随后用去离子水冲洗，而不是重复NaOCl冲洗，以研究钙芒硝和碳酸盐。使用新方案对先前发表的数据进行重新分析，提供了使用该方案显著提高数据质量的证据。
The aim of this study was to evaluate the existing methods for extracting trace sulfate from francolite and measuring its concentration and sulfur isotope composition. Phosphatic rocks were chemically and thermally treated to remove non‐structural SO42− in francolite, which would otherwise be inadvertently included in geochemical analyses of the structurally‐bound sulfate. Acetic acid (10% v/v) proved to be effective in removing calcite, dolomite and ankerite without affecting francolite. To remove all ‘easily’ soluble sulfates, such as Ca‐sulfates and adsorbed sulfate, rinsing with 10% v/v NaCl had to be repeated several times for most samples. For subsequent S isotope determination sample combustion at 600 °C was found to be an efficient way to remove non‐francolite S‐bearing phases. From a number of SO42− detection methods tested, ICP‐AES proved to be the most accurate. For francolite‐sulfate recovery, our recommended protocol involved repeated rinsing of powdered phosphorites with 10% NaCl as well as NaOCl, and testing of the filtrate for SO42− in each wash. If only S isotope compositions are needed, combustion at 600 °C with a subsequent de‐ionised water rinse could be undertaken instead of repeated NaOCl rinsing for studies of both francolite and carbonate. Re‐analysis of previously published data, using the new protocol, provided evidence that the use of this protocol considerably improves data quality.