Coprecipitation of metal ions into calcite: an estimation of partition coefficients based on field investigation
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ORIGINAL ARTICLE
Coprecipitation of metal ions into calcite: an estimation of partition coefficients based on field investigation Zhongwei Wang1,2 • Jiubin Chen1,3 • Hongming Cai3 • Wei Yuan3 Shengliu Yuan3
•
Received: 4 September 2020 / Revised: 26 October 2020 / Accepted: 12 November 2020 Ó Science Press and Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Trace elements (and their isotopes) in carbonates are commonly used to reconstruct paleoenvironment and paleoclimate. Understanding the processes and mechanisms of element incorporation into carbonates is thus crucial for using such geochemical parameters as paleoclimate proxies. In contrast to laboratory-based experimental results, the partitioning of trace metals between solid and solution phases in natural carbonate precipitation systems has rarely been reported. In this study, we investigated the partition coefficients of metal ions between solid and solution in the channel of the natural Baishuitai travertine system, Yunnan, China. Our results show that the partition coefficients of Li?, Na?, Mg2?, Sr2? and Ba2? are \ 1, that of Ni2? is approximately 1, and those of Co2?, Mn2?, Zn2? and Cu2? are [ 1, consistent with the results found in previous experimental studies. Although
the substitution for Ca2? is likely the main uptake process of these metals into calcite, depending on their ionic radius and charge, trace elements may also be incorporated by adsorption or physical entrapment. Our study shows that unlike laboratory experiments performed under specific conditions, the partitioning of metals between two phases in the natural travertine system could be controlled by several, even multiple, environmental factors (e.g., carbonate deposition rate, temperature, and pH), which should be taken into account when using trace metals (and their isotopes) in carbonate archives as a paleoclimate proxy. Keywords Metal ions Coprecipitation Calcite Partition coefficients Field investigation
1 Introduction & Jiubin Chen [email protected] Zhongwei Wang [email protected] Hongming Cai [email protected] Wei Yuan [email protected] Shengliu Yuan [email protected] 1
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
School of Earth System Science, Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China
Trace elements in carbonates are widely used for investigating and reconstructing the past surface environment and climate. The process and mechanism of the incorporation of elements into carbonate are the factors restricting the use of such geochemical parameters as paleoclimate proxies. Carbonate minerals mainly consist of calcite, aragonite, and dolomite, with Ca2? and Mg2? as the major cations (Gaffey 1987). As the radius and electrovalence of the cation Sr2? are similar to those of Ca2?, Sr2? can replace Ca2
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